Enzyme replacement therapy with idursulfase for mucopolysaccharidosis type II (Hunter syndrome)

  • Review
  • Intervention

Authors


Abstract

Background

Mucopolysaccharidosis II, also known as Hunter syndrome, is a rare, X-linked disease caused by a deficiency of the lysosomal enzyme iduronate-2-sulfatase, which catalyses a step in the catabolism of glycosaminoglycans. The glycosaminoglycans accumulate within tissues affecting multiple organs and physiologic systems. The clinical manifestations include neurologic involvement, severe airways obstruction, skeletal deformities and cardiomyopathy. The disease has a variable age of onset and variable rate of progression. In those with severe disease, death usually occurs in the second decade of life, whereas those patients with less severe disease may survive into adulthood. Enzyme replacement therapy with intravenous infusions of idursulfase has emerged as a new treatment for mucopolysaccharidosis type II.

Objectives

To evaluate the effectiveness and safety of enzyme replacement therapy with idursulfase compared to other interventions, placebo or no intervention, for treating mucopolysaccharidosis type II.

Search methods

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Trials Register (date of last search 22 July 2013).

We also searched EMBASE, PubMed and the Literature Latino-Americana e do Caribe em Ciências da Saúde (LILACS) (date of last search 09 July 2013).

Selection criteria

Randomised and quasi-randomised controlled trials of enzyme replacement therapy with idursulfase compared to no intervention, placebo or other options (e.g. behavioral strategies, transplantation).

Data collection and analysis

Two authors independently screened the trials identified, appraised quality of papers and extracted data.

Main results

One study (96 patients) met the inclusion criteria, although the primary outcome of this review - z score for height and weight, was not assessed in the study. This trial was considered to be of overall good quality. Following 53 weeks of treatment, patients in the weekly idursulfase 0.5 mg/kg group demonstrated a significant improvement rate compared with placebo for the primary outcome: distance walked in six minutes on the basis of the sum of ranks of change from baseline, mean difference 37.00 (95% confidence interval 6.52 to 67.48). The every-other-week idursulfase 0.5 mg/kg group also showed an improvement, which was not significant compared with placebo, mean difference 23.00 (95% confidence interval -4.49 to 50.49). After 53 weeks, there was no statistical significance difference in per cent predicted forced vital capacity between the three groups and absolute forced vital capacity was significantly increased from baseline in the weekly dosing group compared to placebo, mean difference 0.16 (95% confidence interval CI 0.05 to 0.27). No difference was observed between the every-other-week idursulfase 0.5 mg/kg group and placebo.

In addition, liver and spleen volumes and urine glycosaminoglycan excretion were significantly reduced from baseline by both idursulfase dosing regimens. Idursulfase was generally well tolerated, but infusion reactions did occur. Idursulfase antibodies were detected in 31.7% of patients at the end of the study and they were related to a smaller reduction in urine glycosaminoglycan levels.

Authors' conclusions

The current evidence is limited. While the randomised clinical trial identified was considered to be of good quality, it failed to describe important outcomes. It has been demonstrated that enzyme replacement therapy with idursulfase is effective in relation to functional capacity (distance walked in six minutes and forced vital capacity), liver and spleen volumes and urine glycosaminoglycan excretion in patients with mucopolysaccharidosis type II compared with placebo. There is no available evidence in the included study and in the literature on outcomes such as improvement in growth, sleep apnoea, cardiac function, quality of life and mortality. More studies are needed to obtain more information on the long-term effectiveness and safety of enzyme replacement therapy.

Resumen

Tratamiento de reemplazo enzimático con idursulfasa para la mucopolisacaridosis tipo II (síndrome de Hunter)

Antecedentes

La mucopolisacaridosis tipo II, también conocida como síndrome de Hunter, es una enfermedad poco frecuente vinculada al cromosoma X y causada por una deficiencia de la enzima lisosomal iduronato-2-sulfatasa, que cataliza un paso en el catabolismo de los glucosaminoglicanos. Los glucosaminoglicanos se acumulan en los tejidos y afectan a órganos y sistemas fisiológicos múltiples. Las manifestaciones clínicas incluyen compromiso neurológico, obstrucción grave de las vías respiratorias, deformidades esqueléticas y miocardiopatía. La enfermedad presenta una edad variable de aparición y una tasa variable de progresión. En los pacientes con enfermedades graves, la muerte ocurre generalmente en la segunda década de la vida, mientras que los pacientes con enfermedades menos graves pueden sobrevivir hasta la edad adulta. El tratamiento de reemplazo enzimático con infusiones intravenosas de idursulfasa ha surgido como un nuevo tratamiento para la mucopolisacaridosis tipo II.

Objetivos

Evaluar la efectividad y la seguridad del tratamiento de reemplazo enzimático con idursulfasa comparado con otras intervenciones, placebo o ninguna intervención, para tratar la mucopolisacaridosis tipo II.

Métodos de búsqueda

Se hicieron búsquedas en el registro de ensayos del Grupo Cochrane de Fibrosis Quística y Enfermedades Genéticas (Cochrane Cystic Fibrosis and Genetic Disorders Group) (fecha de la última búsqueda 22 julio 2013).

También se hicieron búsquedas en EMBASE, PubMed y en Literature Latino-Americana e do Caribe em Ciências da Saúde (LILACS) (fecha de la última búsqueda 9 julio 2013).

Criterios de selección

Ensayos controlados con asignación aleatoria y cuasialeatoria del tratamiento de reemplazo enzimático con idursulfasa en comparación con ninguna intervención, placebo u otras opciones (p.ej., estrategias conductuales, trasplante).

Obtención y análisis de los datos

Dos autores examinaron de forma independiente los ensayos identificados, evaluaron la calidad de los artículos y extrajeron los datos.

Resultados principales

Un estudio (96 pacientes) cumplió con los criterios de inclusión, aunque el resultado primario de esta revisión - puntuación z para la altura y el peso - no fue evaluada en el estudio. En general, este ensayo se considera de buena calidad. Después de 53 semanas de tratamiento, los pacientes en el grupo de idursulfasa semanal de 0,5 mg/kg demostraron una tasa significativa de mejoría en comparación con placebo para el resultado primario: distancia de caminata en seis minutos sobre la base de la suma de los rangos del cambio desde el inicio, diferencia de medias 37,00 (intervalo de confianza del 95%: 6,52 a 67,48). El grupo de idursulfasa de 0,5 mg/kg en semanas alternadas también mostró una mejoría, que no fue significativa en comparación con placebo, diferencia de medias 23,00 (intervalo de confianza del 95%: -4,49 a 50,49). Después de 53 semanas, no hubo diferencias estadísticamente significativas en el porcentaje teórico de la capacidad vital forzada entre los tres grupos y la capacidad vital forzada absoluta aumentó significativamente desde el inicio en el grupo de dosificación semanal comparado con el placebo, diferencia de medias 0,16 (intervalo de confianza [IC] del 95%: 0,05 a 0,27). No se observó ninguna diferencia entre el grupo de idursulfasa de 0,5 mg/kg en semanas alternas y el placebo.

Además, los volúmenes hepáticos y esplénicos y la excreción de glucosaminoglicanos en la orina se redujeron significativamente desde el inicio mediante ambos regímenes de dosificación con idursulfasa. La idursulfasa generalmente fue bien tolerada, aunque ocurrieron reacciones a las infusiones. Se detectaron anticuerpos contra la idursulfasa en un 31,7% de los pacientes al final del estudio y estuvieron relacionados con una reducción más pequeña en los niveles de glucosaminoglicano en la orina.

Conclusiones de los autores

Las pruebas actuales son limitadas. Aunque se consideró que el ensayo clínico con asignación aleatoria identificado era de buena calidad, no logró describir resultados importantes. Se demostró que el tratamiento de reemplazo enzimático con idursulfasa es efectivo con relación a la capacidad funcional (distancia de caminata en seis minutos y capacidad vital forzada), los volúmenes hepáticos y esplénicos y la excreción de glucosaminoglicanos en la orina en pacientes con mucopolisacaridosis tipo II en comparación con el placebo. No hay pruebas disponibles en el estudio incluido ni en la bibliografía sobre resultados como la mejoría en el crecimiento, la apnea del sueño, la función cardíaca, la calidad de vida y la mortalidad. Se necesitan más estudios para obtener más información sobre la efectividad y la seguridad a largo plazo del tratamiento de reemplazo enzimático.

Résumé scientifique

Enzymothérapie de substitution avec idursulfase pour la mucopolysaccharidose de type II (syndrome de Hunter)

Contexte

La mucopolysaccharidose de type II, également connue sous le nom de syndrome de Hunter, est une maladie rare liée au chromosome X, causée par un déficit d’iduronate-2-sulfatase, une enzyme lysosomale qui catalyse une étape dans le catabolisme des glucosaminoglycanes. Les glucosaminoglycanes s’accumulent dans les tissus en affectant de multiples organes et systèmes physiologiques. Les manifestations cliniques comprennent des atteintes neurologiques, une obstruction grave des voies aériennes, des déformations du squelette et une cardiomyopathie. L’âge auquel la maladie apparaît est variable, tout comme l’est la vitesse de progression. Chez les patients gravement touchés par la maladie, le décès survient généralement avant 20 ans alors que les patients moins gravement touchés peuvent survivre à l’âge adulte. L’enzymothérapie de substitution avec perfusions en intraveineuse d’idursulfase a fait son apparition comme nouveau traitement de la mucopolysaccharidose de type II.

Objectifs

Evaluer l’efficacité et la sécurité de l’enzymothérapie de substitution avec idursulfase par rapport aux autres interventions, au placebo ou à aucune intervention, pour traiter la mucopolysaccharidose de type II.

Stratégie de recherche documentaire

Nous avons fait des recherches dans le Registre d’essais du groupe Cochrane sur la fibrose kystique et les troubles génétiques (date de la dernière recherche, le 22 juillet 2013).

Nous avons également effectué des recherches dans EMBASE, PubMed et dans la Literature Latino-Americana e do Caribe em Ciências da Saúde (LILACS) (date de la dernière recherche, 9 juillet 2013).

Critères de sélection

Essais contrôlés randomisés ou quasi-randomisés de l’enzymothérapie de substitution avec idursulfase par rapport à aucune intervention, au placebo ou aux autres options (par ex. stratégies comportementales, transplantation).

Recueil et analyse des données

Deux auteurs ont revus indépendamment les essais identifiés, ils ont évalué la qualité des essais et extrait les données.

Résultats principaux

Une étude (soit 96 patients) répondait aux critères d’inclusion, bien que le critère principal d’évaluation de cette revue – score z pour la hauteur et le poids-, n’était pas évalué dans l’étude. Cet essai a été considéré comme de bonne qualité générale. Après 53 semaines de traitement, les patients du groupe qui recevaient 0,5 mg/kg d’idursulfase chaque semaine ont montré un taux d’amélioration significatif par rapport au placebo pour le critère principal d’évaluation : distance parcourue en six minutes sur la base de la somme des classes de changement par rapport au niveau de départ, différente moyenne 37,00 (intervalle de confiance 95% 6,52 à 67,48). Le groupe recevant 0,5 mg/kg d’idursulfase toutes les deux semaines a également montré une amélioration, non significative par rapport au placebo, soit une différence moyenne de 23,00 (intervalle de confiance 95 % -4,49 à 50,49). Après 53 semaines, il n’y avait pas de différence statistiquement significative en pourcentage concernant la capacité vitale forcée prédite entre les trois groupes et la capacité vitale forcée absolue avait augmenté de manière significative par rapport au niveau de départ dans le groupe avec dosage hebdomadaire par rapport au placebo, soit une différence moyenne de 0,16 (intervalle de confiance 95 % 0,05 à 0,27). Aucune différence n’a été observée entre le groupe avec dosage de 0,5 mg/kg d’idursulfase toutes les deux semaines et le placebo.

De plus, les volumes du foie et de la rate et l’excrétion urinaire de glucosaminoglycanes avaient baissé de manière significative par rapport au niveau de départ dans les deux posologies. L’idursulfase a été généralement bien tolérée, mais des réactions à la perfusion sont apparues. Des anticorps anti-idursulfase ont été détectés chez 31,7 % des patients à la fin de l’étude et ils étaient associés à une réduction plus faible des taux de glucosaminoglycanes urinaires.

Conclusions des auteurs

Les preuves actuelles sont limitées. Même si l’essai clinique randomisé identifié était considéré comme étant de bonne qualité, il n’a pas réussi à décrire des résultats importants. Il a été démontré que l’enzymothérapie de substitution avec idursulfase est efficace concernant la capacité fonctionnelle (distance parcourue en six minutes et capacité vitale forcée), les volumes du foie et de la rate et l’excrétion urinaire de glucosaminoglycanes chez les patients atteints de mucopolysaccharidose de type II par rapport au placebo. Il n’existe aucune preuve disponible dans l’étude incluse et dans les documentations sur des critères telles que l’amélioration de la croissance, l’apnée du sommeil, la fonction cardiaque, la qualité de vie et la mortalité. Des études supplémentaires sont nécessaires pour obtenir plus d’informations sur l’efficacité à long terme et la sécurité de l’enzymothérapie de substitution.

Plain language summary

Enzyme replacement therapy with idursulfase for mucopolysaccharidosis type II (Hunter syndrome)

Hunter syndrome or mucopolysaccharidosis II is a rare genetic disease that occurs when an enzyme that the body needs is either missing or malfunctioning. The body doesn't have adequate supplies of this enzyme to break down certain complex molecules, so these molecules build up in harmful amounts in certain cells and tissues. The build-up that occurs in Hunter syndrome eventually causes permanent, progressive damage affecting appearance, mental development, organ function and physical abilities. Hunter syndrome appears in children as young as the age of two years and it nearly always occurs in males. In the past, treatment of Hunter syndrome has been limited to the relief of symptoms and complications. Enzyme replacement therapy with idursulfase aims to replace iduronate-2-sulfatase, the enzyme that is deficient or absent in people with Hunter syndrome. However, given its high cost it is essential to assess how effective and safe this treatment is. Current evidence is limited because there was only one randomised clinical trial found in the medical literature. The quality of this trial was considered good and compared with placebo, enzyme replacement therapy with idursulfase in people with Hunter syndrome, led to some improvement in the patients' ability to walk and a reduction in the excretion of  abnormal mucopolysaccharides in the urine. To date there is no evidence available in the literature showing that treatment reduces complications of the disease related to quality of life and mortality.

Resumen en términos sencillos

Tratamiento de reemplazo enzimático con idursulfasa para la mucopolisacaridosis tipo II (síndrome de Hunter)

El síndrome de Hunter o mucopolisacaridosis II es una enfermedad genética poco frecuente que se presenta cuando una enzima que el cuerpo necesita está ausente o funciona de forma deficiente. El cuerpo no posee suministros adecuados de esta enzima para descomponer ciertas moléculas complejas, de manera que estas moléculas se acumulan en cantidades perjudiciales en ciertas células y tejidos. La acumulación que se presenta en el síndrome de Hunter con el tiempo causa daño permanente y progresivo que afecta la apariencia, el desarrollo mental, la función orgánica y las capacidades físicas. El síndrome de Hunter aparece en niños de sólo dos años de edad y casi siempre ocurre en los hombres. Anteriormente, el tratamiento del síndrome de Hunter estaba limitado al alivio de los síntomas y las complicaciones. El tratamiento de reemplazo enzimático con idursulfasa intenta reemplazar la iduronato-2-sulfatasa, la enzima que es deficiente o que está ausente en los pacientes con síndrome de Hunter. Sin embargo, debido al costo elevado, es esencial evaluar cuán efectivo y seguro es este tratamiento. Las pruebas actuales son limitadas debido a que hubo sólo un ensayo clínico con asignación aleatoria encontrado en la bibliografía médica. La calidad de este ensayo se consideró buena y comparado con placebo, el tratamiento de reemplazo enzimático con idursulfasa en los pacientes con síndrome de Hunter, dio lugar a una cierta mejoría en la capacidad de los pacientes para caminar y a una reducción en la excreción anormal de mucopolisacáridos en la orina. Hasta la fecha, no hay pruebas disponibles en la bibliografía que indiquen que el tratamiento reduce las complicaciones de la enfermedad relacionadas con la calidad de vida y la mortalidad.

Notas de traducción

La traducción y edición de las revisiones Cochrane han sido realizadas bajo la responsabilidad del Centro Cochrane Iberoamericano, gracias a la suscripción efectuada por el Ministerio de Sanidad, Servicios Sociales e Igualdad del Gobierno español. Si detecta algún problema con la traducción, por favor, contacte con Infoglobal Suport, cochrane@infoglobal-suport.com.

Résumé simplifié

Enzymothérapie de substitution avec idursulfase pour la mucopolysaccharidose de type II (syndrome de Hunter)

Le syndrome de Hunter ou mucopolysaccharidose de type II est une maladie génétique rare qui survient lorsqu’une enzyme dont le corps a besoin est absente ou ne fonctionne pas bien. Le corps ne dispose pas de quantités adéquates de cette enzyme pour détruire certaines molécules complexes, ces dernières s’accumulent donc en quantités nocives pour certaines cellules ou certains tissus. Le développement qui apparait dans le syndrome de Hunter cause à terme des dommages progressifs permanents qui affectent l’apparence, le développement mental, la fonction de certains organes et les capacités physiques. Le syndrome de Hunter apparait chez les enfants dès l’âge de deux ans et touche quasiment toujours les garçons. Dans le passé, le traitement du syndrome de Hunter était limité au soulagement des symptômes et des complications. L’enzymothérapie de substitution avec idursulfase vise à remplacer l’iduronate-2-sulfatase, l’enzyme qui est déficiente ou absente chez les personnes atteintes du syndrome de Hunter. Pour autant, au vu de son coût élevé, il est indispensable d’évaluer l’efficacité et la sécurité de ce traitement. Les preuves actuelles sont limitées parce qu’il n’y avait qu’un essai clinique randomisé disponible dans la litterature médicale. Cet essai a été considéré comme de bonne qualité générale et par rapport au placebo, l’enzymothérapie de substitution avec idursulfase chez les personnes atteintes du syndrome de Hunter a conduit à une certaine amélioration de la capacité à marcher des patients et à une baisse de l’excrétion de mucopolysaccharides anormaux dans les urines. A ce jour, il n’y a pas de preuve disponible dans la littérature indiquant que le traitement atténue les complications de la maladie telles que la qualité de vie et à la mortalité.

Notes de traduction

Translated by: French Cochrane Centre

Translation supported by: Ministère du Travail, de l'Emploi et de la Santé Français

Background

Description of the condition

Mucopolysaccharidosis II (MPS II or Hunter syndrome) belongs to a group of inherited diseases of glycosaminoglycan (GAG) catabolism called mucopolysaccharidoses. The GAGs are oligosaccharide components of the proteoglycans, macromolecules responsible for the integrity and function of connective tissue. Mucopolysaccharidoses are caused by a lysosomal enzyme deficiency for the stepwise degradation of the GAGs. All of the mucopolysaccharidoses are of recessive autosome inheritance, except MPS II, which is an X-linked recessive disease. The syndrome was described by Charles Hunter in 1917 and is the result of a deficiency of iduronate-2-sulfatase (I2S), with consequent increase of the urinary concentration of the GAGs dermatan sulphate and heparan sulphate. The clinical phenotype of MPS II is characterised by progressive pathological lysosomal storage of GAGs in nearly all cell types, tissues and organs. The iduronate 2-sulfatase gene is located on chromosome Xq28, and more than 350 mutations have been identified to date, including different deletions, splice-site and point mutations. This genetic heterogeneity may explain the high degree of clinical heterogeneity in MPS II (Martin 2008; Wraith 2008a).

This is a rare disease with an estimated incidence of approximately 1 in 162,000 live births. Although males are predominantly affected, a small number of affected females have been described (Meikle 1999; Tuschl 2005). This is a variable, progressive, multisystem disease and should be regarded as a continuum between two extremes (severe and attenuated). Two-thirds of patients present central nervous system (CNS) involvement, representing the more severe form, with clinical features appearing between two and four years of age. In these cases, the progressive neurologic involvement is prominent and leads to severe mental impairment; death usually occurs in the first or second decade of life, usually because of obstructive airway disease or cardiac failure (or both) associated with loss of neurologic function. At the opposite end of the spectrum, clinical signs and symptoms have a slightly later onset and the neurologic dysfunction may be minimal, but with obvious somatic involvement, and longer survival (Wraith 2008a). Data from the 'Hunter Outcome Survey' (HOS), the only large-scale, multinational observational study of patients with MPS II, showed that median age at death was significantly lower in patients with cognitive involvement compared with those without cognitive involvement (11.7 versus 14.1 years; P = 0.024) (Jones 2008).

The most common clinical signs and symptoms include dysostosis multiplex with decreased range of joint motion, coarse facial features, enlarged tongue, hearing loss, abnormal dentition, upper airway obstruction with or without sleep apnoea, restrictive lung disease, hepatosplenomegaly, cardiomyopathy, skeletal deformities, and severe short stature (Young 1983). 

The development of children with MPS II seems normal in the first months of life, but the outcome is highly changeable. Even in individuals with attenuated disease, cranial magnetic resonance imaging (MRI) scans are often grossly abnormal, with extensive white matter changes as well as dilated perivascular spaces, despite apparently normal intellectual skills. Individuals with more severe MPS II also appear normal at birth, and early development may be normal. Some individuals fail hearing screening tests in the first year, and speech delay is not unusual in those more severely affected. By 18 to 24 months developmental delay is usually apparent. Most individuals make very slow progress after this stage, with a developmental plateau beginning between three and five years of age. Unlike children with severe MPS I, who are usually placid, more severely affected children with MPS II can be hyperactive and aggressive. One of the most important limitations beside the neurologic involvement in individuals suffering from MPS II, is the impact that the progressive physical abnormalities have on their quality of life. Due to a combination of the bone disease, decreased respiratory capacity and impaired cardiac function, they suffer from chronic, severely diminished endurance. With the disease progression their ability to walk even short distances may be lost and eventually many patients become wheelchair-bound. By the time of death in their second decade, most individuals with CNS involvement show severe learning difficulties and are dependant on care providers for all their needs (Wraith 2008a). 

The measurement of urinary GAGs (heparan and dermatan sulphate) is the usual first screening test for MPS II. As in almost all cases of MPS, the total urinary GAG level is increased. However, this is not diagnostic of MPS II, so additional tests must be performed. Futhermore, a negative urine GAG test does not necessarily rule out a diagnosis of MPS II, because false-negative results can occur as a result of a lack of sensitivity of the testing method (de Jong 1992). Definitive diagnosis is established by enzyme assay in leukocytes, fibroblasts or plasma, using substrates specific for I2S. Absent or low I2S activity in males is diagnostic of MPS II, provided that multiple sulphatase deficiency is excluded by finding normal activity of another sulphatase. Absolute enzyme activity cannot be used to predict the severity of the phenotype. Mutation analysis may be used to confirm Hunter syndrome in males. However, it is difficult to establish a genotype-phenotype correlation to provide an indication of the likely prognosis, this is because patients carrying the same alterations may present different phenotypes, suggesting that others factors may modulate the clinical phenotype (Kresse 1982;Martin 2008; Neufeld 2001).

As the definition of effective treatment for MPS II is "an improvement in or a prevention of progression of disease activity as indicated by a stabilisation in clinical condition associated with an improvement in the abnormalities present at baseline" (Vellodi 2007), the primary endpoints for the evaluation of interventions for the treatment of this condition should reflect improvement in important signs and symptoms observed in the disease, such as a change in the speed of growth and in the impairment of cardiac and respiratory system.

The usual management of MPS II has been palliative and focused on the treatment of signs and symptoms. Care for the person with MPS II involves a multidisciplinary approach and includes paediatricians, neurologists, orthopedists, otolaryngologists, ophthalmologists, and occupational and physical therapists, as well as geneticists and counsellors (National Horizon Scanning Centre 2005). Hemapoietic stem cell transplantation (HSCT) by bone marrow transplantation, human amnion membrane implantation, fibroblast transplantation, serum or plasma infusion has been suggested as a means of providing donor cells capable of expressing I2S, but the results are disappointing and long-term outcomes are limited, therefore, HSCT is not currently recommended for individuals with MPS II (Martin 2008).

Description of the intervention

Recently idursulfase (Elaprase®, Shire Human Genetic Therapies, Inc, Cambridge, MA), a recombinant human I2S produced in a human cell line, was approved in the United States of America and the European Union for the treatment of MPS II.

How the intervention might work

The rationale for therapy is that exogenous I2S would replace the I2S that is deficient in patients and either stop or reverse disease progression. Idursulfase is produced in a continuous human cell line and is a purified form of the natural lysosomal enzyme I2S. Mannose-6-phosphate (M6P) residues on the oligosaccharide chains of the glycoprotein enzyme and allows specific binding of idursulfase to M6P receptors on the cell surface, leading to cellular internalisation and targeting of the enzyme to lysosomes, and subsequent catabolism of accumulated GAGs (Wraith 2008b).

Why it is important to do this review

There is no definitive treatment for people diagnosed with MPS II. The appearance of a promising therapeutic strategy, idursulfase, makes it necessary to map the knowledge in this area based on the rigor inherent to systematic reviews by considering relevant aspects of the effectiveness and safety of this therapeutic strategy for relevant clinical issues.

The current publication is a minor update of a Cochrane review first published in 2011 (da Silva 2011).

Objectives

To evaluate the effectiveness and safety of enzyme replacement therapy with idursulfase compared to other interventions, placebo or no intervention, for treating mucopolysaccharidosis type II.

Methods

Criteria for considering studies for this review

Types of studies

Randomised and quasi-randomised controlled clinical trials of parallel or cross-over design.

Types of participants

Individuals with MPS II (Hunter syndrome) of any age and any degree of disease severity. Diagnosis should be established by enzyme assay in leukocytes, fibroblasts or plasma, using substrates specific for I2S.

Types of interventions

Enzyme replacement therapy with idursulfase in any amount given for a period of at least one month compared to:

  • no intervention;

  • placebo;

  • other options (e.g. behavioral strategies, transplantation).

Types of outcome measures

Following further advice from the Cochrane Cystic Fibrosis and Genetic Disorders Editorial Team, we have made post hoc changes to the outcomes. Previously listed as primary outcomes - 'left ventricular mass index' and 'overnight apnoea-hypopnoea index (AHI)' have been re-allocated to secondary outcomes. The six-minute walk test (6MWT) has been re-allocated from secondary outcomes to primary outcomes. Given that MPS II is a disease with multiorgan and multisystem involvement, a variable age of onset and a variable rate of progression, we found the choice of representative outcomes a challenge. Since appropriate growth is a key clinical feature in children and this is altered in all forms of MPS II, we selected z score of weight and height as the primary outcome (Martin 2008; Wraith 2008a). As studies may include adults, the functional capacity test 6MWT was also selected as a primary outcome because this standardized test is the most often used to measure functional capacity (ATS 2002). Outcomes that represent changes in other organs and systems are listed as secondary.

Primary outcomes
  1. Z scores for

    1. height

    2. weight

  2. Six-minute walk test (6MWT)

Secondary outcomes
  1. Lung function

    1. forced expiratory volume at one second (FEV1)

    2. forced vital capacity (FVC)

    3. any other measure of lung function (e.g. Rint)

  2. Overnight apnoea-hypopnoea index (AHI)

  3. Left ventricular mass index

  4. Joint mobility score (using a validated scoring system)

  5. Liver and spleen volume (measured by abdominal MRI)

  6. Quality of life (using a validated scoring system)

  7. Pain (using a validated scoring system e.g. visual analogue scales (VAS))

  8. Rate of hospitalizations

  9. Resources required for home care support

  10. Changes in glycosaminoglycans (GAGs) urinary excretion

  11. Developmental score

  12. Audiologic assessment (e.g. pure tone audiogram, distortion product otoacoustic emission (DPOE), evoked responses)

  13. Age at death

  14. Adverse effects (AE) and toxicity of treatment

Search methods for identification of studies

Electronic searches

There was no language restriction and the trials were identified from the sources listed below.

We identified relevant trials from the Cochrane Cystic Fibrosis and Genetic Disorders Group's Inborn Errors of Metabolism Trials Register using the term: mucopolysaccharidosis.

This register was compiled from electronic searches of the Cochrane Central Register of Controlled Trials (CENTRAL) (updated each new issue of The Cochrane Library), quarterly searches of MEDLINE and the prospective handsearching of the Journal of Inherited Metabolic Disease. Unpublished work were identified by searching through the abstract books of the Society for the Study of Inborn Errors of Metabolism conference and the SHS Inborn Error Review Series. For full details of all searching activities for the register, please see the relevant section of the Cystic Fibrosis and Genetic Disorders Group Module.

We also searched Embase (1980 to 09 July 2013), PubMed (1980 to 09 July 2013) and the Literature Latino-Americana e do Caribe em Ciências da Saúde - LILACS (1982 to 09 July 2013). The search strategy was composed of the terms 'enzyme replacement therapy' and 'Mucopolysaccharidosis II'. We searched with both, subject headings and free text words (see Appendix 1; Appendix 2; Appendix 3).

Date of most recent search of the Group's Inborn Errors of Metabolism Trials Register: 22 July 2013.

Searching other resources

Reference lists of any identified relevant studies were scrutinized for additional citations.

Data collection and analysis

Selection of studies

Two authors (EMKS and LAS) independently screened the studies identified by the literature search. When disagreements occurred they consulted a third author (RBA) and did not include data until they reached a consensus.

Data extraction and management

Two authors (EMKS and LAS) extracted data independently; they resolved discrepancies in the results by discussion. The authors used a standard form to extract the following information: characteristics of the study (design, method of randomisation); participants; interventions; and outcomes (types of outcome measures, timing of outcomes, adverse events).

The authors planned to report outcomes at up to and including three months, over three months and up to six months, over six months and up to twelve months and then annually thereafter. They also planned to consider additional follow-up data recorded at more than 12 months. Given only one trial is currently included they have reported these data at 53 weeks, as within the trial.

The included trial reported standard errors (SE) ; the authors converted these to standard deviations (SD) (SD = SE x  square root of n).

Assessment of risk of bias in included studies

In order to assess the risk of bias, two review authors independently assessed the quality of the studies included in the review according to the criteria described in the Cochrane Handbook For Systemtic Review of Interventions (Higgins 2011a).

They assessed the following domains as having either a low, unclear or high risk of bias.

  1. Was the sequence generation adequate?

  2. Was allocation adequately concealed?

  3. Was knowledge of the allocated interventions adequately prevented during the study?

  4. Were incomplete outcome data adequately addressed?

  5. Are reports of the study free of suggestion of selective outcome reporting?

  6. Was the study apparently free of other problems that could put it at a high risk of bias?

The authors reported these assessments for each individual study in the 'Risk of bias' table in the section 'Characteristics of included studies'.

If necessary, for future updates, they plan to contact the study author(s) to seek clarification in case of uncertainty over data.

Measures of treatment effect

For dichotomous variables, the authors calculated the risk ratio (RR) and 95% confidence intervals (CIs). For continuous outcomes, they calculated the mean difference (MD) and 95% CIs. In this review the authors did not identify studies in which the authors did not publish or make available the necessary information to be included in the review. For further studies identified in subsequent updates of this review, the authors will insert any data from primary studies which are not parametric (e.g. effects reported as medians, quartiles, etc) or without sufficient statistical informations (e.g., SDs, number of patients, etc) into an 'Additional table'.

Unit of analysis issues

The unit of analysis is based on the individual participant (unit to be randomised for interventions to be compared), i.e. the number of observations in the analysis should match the number of individuals randomised. The authors did not identify trials with a cross-over design, if in subsequent updates they include such trials, they will use only first-arm data (before participants have crossed over the treatments) (Elbourne 2002).

Dealing with missing data

Irrespective of the type of data, the authors reported dropout rates in the Characteristics of included studies table and they used intention-to-treat analysis (Higgins 2011b).

Assessment of heterogeneity

As the authors only included one study they did not evaluate heterogeneity. In future updates, they will qualify inconsistency among the pooled estimates using the I2 = [(Q - df)/Q] x 100% test, where Q is the chi-squared statistic and df its degrees of freedom. This illustrates the percentage of the variability in effect estimates resulting from heterogeneity rather than sampling error (Higgins 2003; Higgins 2011a). The thresholds for the interpretation of I2 will be as follows: 0% to 25% low heterogeneity; 25% to 75% moderate heterogeneity; and more than 75% significant heterogeneity (Higgins 2003).

Assessment of reporting biases

In future updates of this review, if a sufficient number of studies (at least 10) are included, the authors will assess publication bias by drawing a funnel plot (trial effect versus trial size).

Data synthesis

Qualitative information

The authors synthesized qualitative information relative to methods, risk of bias, description of participants and outcome measures and inserted this information in the table of Characteristics of included studies.

Quantitative information

For dichotomous variables, the authors calculated the RR and 95% CIs. For continuous variables, we calculated the MD and 95% CIs.

In subsequent updates of this review, if continuous data relate to the same outcome, but are measured with different instruments (different and not interchangeable units of measure), the authors will pool these data using the standardised mean difference (SMD). For all statistical methods when pooling data, they will report the 95% CIs. If they do not identify any significant heterogeneity, they will compute pooled estimates of the treatment effect for each outcome under a fixed-effect model. Otherwise, if they identify significant heterogeneity, they will perform a random-effects analysis.

Subgroup analysis and investigation of heterogeneity

In subsequent updates of this review, If the authors find significant heterogeneity, they will investigate the possible causes of this further by exploring the impact of the condition of the individuals (i.e. severity of disease, duration of treatment). If they find sources of heterogeneity and if there are sufficient data, they will conduct meta-analyses by subgroups (by types of dosage and duration of intervention, disease stage, age at onset).

Sensitivity analysis

As only one study was included in this review, the authors did not perform any sensitivity analyses, but will do so if there are an adequate number of studies included in future updates. If, in the future, they are able to perform a sensitivity analysis, they will do so with an aim to explore possible causes of heterogeneity and the robustness of the results.

We will include the following factors in any sensitivity analysis, separating studies according to:

  1. allocation concealment quality (low, unclear or high risk);

  2. blinding of participants, caregiver and outcome assessment (low, unclear or high risk, or not performed);

  3. rates of withdrawal for each outcome;

  4. length of follow-up;

  5. age of participants;

  6. disease severity.

Results

Description of studies

Results of the search

There were 163 records identified by the searches: MEDLINE (Pubmed): 101 references to studies; Cochrane Cystic Fibrosis and Genetic Disorders Group's Trials Register: 7 references; EMBASE: 60 references; LILACS: 2 references. The authors also scrutinised the bibliographical references of these papers for further potentially eligible studies and found no additional references. After closer examination of the titles and abstracts of these references, all but five studies were subsequently excluded from further analysis. Full text copies of these five remaining studies were obtained and were then subjected to further assessment. Following the verification of five whole studies, only one of them fulfilled all the inclusion criteria of this review (Muenzer 2006) and four studies were excluded (Muenzer 2007; Gutiérrez-Solana 2007; Tylki-Szymanska 2008; Sohn 2013) (Figure 1).

Figure 1.

Study flow diagram.

Included studies

Trial Design

The included study was a multicentre, multi-national, double-blind, randomised, placebo-controlled, 53-week, phase II/III study of the efficacy and safety of idursulfase 0.5 mg/kg administered either weekly or every-other week (EOW) in patients with MPS II (Muenzer 2006).

Participants

The study included 96 patients with MPS II. The biochemical evidence of MPS II included a documented deficiency in the I2S enzyme activity of less than or equal to 10% of the lower limit of the normal range measured in plasma, fibroblasts or leukocytes combined with a normal enzyme activity level of another sulfatase. All patients were required to reproducibly perform pulmonary function testing and have an abnormal FVC of less than 80% of predicted. Patients who had a tracheotomy or who had received a bone marrow or cord blood transplant were excluded from the study. All 96 randomised patients were male between the ages of 4.9 and 30.9 years. The mean (SD) age of patients in this study was 13.1 years (1.22), 14.4 years (1.20) and 15.1 years (1.11) for the placebo, idursulfase 0.5 mg/kg EOW and idursulfase 0.5 mg/kg weekly groups respectively. Nearly 45% of patients in the study were 5 to 11 years old and 25% of patients were 19 years of age or older. There was no significant difference of age distribution among the three groups. Patients were also stratified according disease score, calculated using the baseline results of the 6MWT and the per cent predicted FVC (% predicted FVC).

Interventions

The 96 patients were randomised in three groups: placebo (n = 32); idursulfase 0.5 mg/kg weekly (n = 32); and idursulfase 0.5 mg/kg EOW (n = 32). Infusions were given over a three-hour period and patients were discharged one hour after completing each infusion provided that they remained clinically stable.

Outcomes

The primary efficacy assessment of the included study was a comparison between the placebo and weekly idursulfase group for the change from baseline to week 53 in a single, two-component composite variable combining % predicted FVC as a measure of respiratory function and 6MWT as a measure of physical functional capacity. The change from baseline to week 53 in % predicted FVC and 6MWT for each patient was calculated. Within each parameter the changes were ranked irrespective of treatment group, with the lowest change value assigned a rank of 1, the next lowest a rank of 2, and so forth. The two-component composite score for each patient was calculated by summing the ranks of the two individual components. The 6MWT was conducted in accordance with American Thoracic Society guidelines (ATS 2002). The secondary efficacy outcome measurements were: passive joint range of motion (JROM); liver and spleen volume by MRI and urinary GAG levels. Data were analysed using analysis of covariance with the treatment groups and study region fitted as factors and baseline patient age and baseline disease score as covariate. All analyses were performed by intention-to treat (ITT) and each variable was quantified as a change from the baseline value.

Excluded studies

A total of four studies were excluded (Gutiérrez-Solana 2007; Muenzer 2007; Sohn 2013; Tylki-Szymanska 2008). One because it was an abstract reporting partial results of an ongoing case-series study (Tylki-Szymanska 2008); one because it was a phase I/II clinical trial that evaluated safety and dosing requirements (Muenzer 2007); one because it was a narrative review (Gutiérrez-Solana 2007); and one because it was a clinical trial phase I/II comparing a new formulation of the enzyme, Idursulfase beta, in two doses with the formulation of idursulfase currently available.

For further information, please refer to the Characteristics of excluded studies table.

Risk of bias in included studies

Allocation

Generation of randomisation sequence was not clear in the included study and we assessed this to have an unclear risk of bias (Muenzer 2006). Authors state that the randomisation was stratified by age and total disease score at baseline.

Allocation concealment was not discussed in the study, which therefore has been categorized as having an unclear risk of bias.

Blinding

The study was double-blind, and all patients received weekly intravenous infusions. Patients randomised to EOW idursulfase dosing received placebo infusion during intervening weeks to maintain blinding. The primary outcome assessment was conducted by a professional who was not involved with the study. We therefore judged the study to have a low risk of bias for blinding of participants, clinicians and outcome assessors.

Incomplete outcome data

Ninety-four (97.9%) of 96 patients completed one year of treatment. The two patients, who did not complete one year of treatment, died during the study: one patient in the placebo group; and one patient in the idursulfase weekly group. Neither death was considered by the investigators to be related to the study drug and analysis was done on an intention-to-treat basis. We have therefore assessed this domain as having a low risk of bias.

Selective reporting

There is concern about selective reporting, due to important clinical outcomes (e.g. z score of height and weight, left ventricular mass index and overnight AHI) not being evaluated and we have assessed this domain as having an unclear risk of bias.

Other potential sources of bias

We believe that the study was free of other problems that could put it at a high risk of bias.

Effects of interventions

In the only included study, patients were randomised into three groups, idursulfase 0.5 mg/kg weekly, EOW and placebo. To evaluate the effect of each treatment the same placebo group was presented in each subgroup in the meta-analyses graphs.

Primary Outcomes

1. Z scores for height and weight

This outcome was not reported in the included study.

2. Six-minute walk test (6MWT)

Following 53 weeks of treatment, patients in the weekly idursulfase 0.5 mg/kg group demonstrated a significant improvement rate compared with placebo of the primary outcome: distance walked in six minutes (6MWT) on the basis of change from baseline, MD 37.00 (95% CI 6.52 to 67.48). The EOW idursulfase 0.5 mg/kg group also showed an improvement but this was not significant compared with placebo, MD 23.00 (95% CI: -4.49 to 50.49) (Analysis 1.1) (Figure 2).

Figure 2.

Forest plot of comparison: 1 Idursulfase 0.5 mg/kg versus placebo, outcome: 1.1 Primary outcome: Six-minute walk test (6MWT).

Secondary Outcomes

1. Lung function
a. FEV1

This outcome was not reported in the included study.

b. FVC

Changes from baseline in % predicted FVC and absolute FVC were reported (Muenzer 2006). After 53 weeks, there was no statistical significance difference in % predicted FVC between the weekly idursulfase group and the placebo group, MD 2.70 (95% CI -2.12 to 7.52) or in the EOW idursulfase group compared with placebo group, MD -0.75 (95% CI -4.98 to 3.49) (Analysis 1.2).

Absolute FVC was significantly increased from baseline in the weekly dosing group compared to placebo, MD 0.16 (95% CI 0.05 to 0.27) after 53 weeks. No difference was observed in absolute FVC between the EOW idursulfase group and placebo, MD 0.01 (95% CI -0.07 to 0.09) (Analysis 1.3).

c. any other measure of lung function (e.g. Rint)

No other measure of lug function was reported in the included study.

2. Overnight apnea-hypopnea index (AHI)

This outcome was not reported in the included study.

3. Left ventricular mass index

This outcome was not reported in the included study.

4. Joint mobility score (using a validated scoring system)

The included study measured changes in passive joint range of motion (JROM) (Muenzer 2006). The authors reported that there were no significant differences between treatment groups but the values observed were not published.

5. Liver and spleen volume (measured by abdominal magnetic resonance imaging (MRI)

The study reported changes from baseline in the liver and spleen volume determined by magnetic resonance imaging (MRI) using the same imaging protocol at all sites (Muenzer 2006). After 53 weeks, in the ITT population, liver volume changed statistically significantly in both idursulfase treatment groups (weekly and EOW) compared with the change in the placebo group, MD -24.50 (95% CI -28.94 to -20.06) and MD -23.20 (95% CI -27.78 to -18.62) respectively (Analysis 1.5).

After 53 weeks in the ITT population, spleen volume were significantly reduced in the idursulfase groups compared to placebo, MD -32.30 (95% IC -41.79 to -22.81) in the weekly group; MD -27.00 (95% IC -37.35 to -16.65) in the idursulfase EOW group (Analysis 1.6).

6. Quality of life (using a validated scoring system)

This outcome was not reported in the included study.

7. Pain (using a validated scoring system e.g. visual analogue scales (VAS))

This outcome was not reported in the included study.

8. Rate of hospitalizations

This outcome was not reported in the included study.

9. Resources required for home care support

This outcome was not reported in the included study.

10. Changes in glycosaminoglycans (GAGs) urinary excretion

Changes from baseline in the GAGs urinary excretion were measured in the included study (Muenzer 2006). Urine GAGs levels decreased in patients treated with either dosing regimen of idursulfase and did not change significantly in patients treated with placebo. At week 53, the changes in the GAGs levels in the idursulfase groups (weekly and EOW) were significantly different than that of the placebo group, MD -207.40 (95% CI -284.85 to -129.95) and MD -173.20 (95% CI -240 to -105.56) respectively (Analysis 1.7).

11. Developmental score

This outcome was not reported in the included study.

12. Audiologic assessment (e.g. pure tone audiogram, distortion product otoacoustic emission (DPOE), evoked responses)

This outcome was not reported in the included study.

13. Age at death

Two deaths occurred during the study (Muenzer 2006). A 24-year-old male in the idursulfase weekly group developed a pulmonary infection, respiratory insufficiency and had a cardiac arrest five days after his first infusion, and he experienced a fatal cardiac arrest seven days later. A second patient, a six-year-old male, who was randomised to placebo developed streptococcus pneumonia following his 34th dose of blinded-study medication, and suffered a lung haemorrhage followed by a fatal cardiac arrest eight days later. The study investigator did not consider either death as being related to the study medication.

14. Adverse effects and toxicity of treatment

No patient was reported to withdraw from the study due to adverse effects (AE). The incidence of AEs were similar across treatment groups within the trial (Muenzer 2006). The most frequently reported AEs during the study (with a excess incidence of at least a 9% compared with placebo in either idursulfase treated group) included headache, nasopharyngitis, abdominal pain, arthralgia and pruritus. All were considered to be consistent with those expected to be seen in an untreated MPS II population. The majority of AEs were reported as mild or moderate in severity in all groups.

Of the AEs considered to be possibly related to idursulfase treatment, the most common were infusion-related. An infusion-related AE was defined as occurring within a day after the infusion began and was judged by the investigator to be possibly or probably related to study treatment. A similar number of patients in each treatment group experienced one or more infusion-related AEs during the study, RR 1.05 (95% CI 0.74 to 1.48) in the weekly group compared to placebo and RR 1.05 (95% CI 0.74 to 1.48) in the EOW group (Analysis 1.8). The incidence of infusion-related AEs was maximal between Weeks 4 and 12 and decreased in all three groups thereafter. Infusion-related AEs reported in the placebo group were similar in nature and severity to those in the idursulfase-treated groups. No patient withdrew from the study because of infusion-related AEs.

A total of 49 serious adverse events (SAEs) occurred in 26 patients during the study: 9 patients in the placebo group experienced a total of 18 SAEs; 8 patients in the idursulfase EOW group experienced a total of 18 SAEs, RR 1.00 (95% CI 0.65 to 1.54); and 9 patients in the idursulfase weekly group experienced a total of 13 SAEs, RR 0.72 (95% CI 0.43 to 1.21) (Analysis 1.9). The majority of these SAEs were considered unrelated to the blinded study medication, although three patients experienced SAEs that were considered by the investigators to be probably or possibly related to the study drug.

Investigators detected IgG anti-idursulfase antibodies in 15 patients (46.9%) in the idursulfase weekly group and in 15 patients (46.9%) in the idursulfase EOW group. In two patients (one from each active treatment group) IgM antibodies were found. The highest prevalence of IgG antibodies was seen at week 27 of the study, when 44.4% of the patients treated with idursulfase were antibody-positive. After 53 weeks, 31.7% of patients in the idursulfase groups remained antibody-positive. The reduction in urine GAG levels in antibody-positive patients was approximately two-thirds of that seen in antibody-negative patients. There was no association with the presence of antibodies and AEs.

15. Other results
Composite score (% predicted FVC + 6MWT)

The efficacy endpoint in the trial included was change from baseline to week 53 in a two-component composite score combining % predicted FVC as a measure of respiratory function and the 6MWT as a measure of functional capacity (Muenzer 2006). The two-component composite score of the idursulfase 0.5 mg/kg weekly group was significantly higher than in the placebo group in the intent-to-treat population, MD 18.96 (95% CI 6.28 to 31.64). A smaller difference was found for the idursulfase EOW compared to placebo groups in the intent-to-treat population, MD 12.86 (95% CI 0.77 to 24.95) (Analysis 1.4). The trial authors reported that the responses between the two idursulfase treatment groups were not significantly different, treatment difference being 10.84 ± 7.11, P = 0.1329).

Discussion

Summary of main results

The evidence available so far are limited to only one randomised clinical trial (Muenzer 2006).The results of the study included in this review show a short-term clinical benefit in patients treated with idursulfase compared with patients treated with placebo. After 53 weeks of treatment, patients in the weekly idursulfase 0.5 mg/kg group demonstrated a statistically significant improvement rate compared with placebo in the distance walked in 6 minutes (6MWT), MD 37.00 (95% CI 6.52 to 67.48). The EOW group also showed improvement but not significant compared with placebo, MD 23.00 (95% CI -4.49 to 50.49). There was no statistically significant difference in % predicted FVC between the three groups and absolute FVC was significantly increased from baseline in the weekly dosing group compared to placebo, MD 0.16 (95% CI 0.05 to 0.27). In addition, urine GAG excretion and liver and spleen volumes were significantly reduced from baseline by both idursulfase dosing regimens.

Idursulfase was generally well tolerated, and the majority of treatment-emergent adverse events were consistent with the natural history of untreated MPS II. The most common treatment-related adverse events were infusion related. Idursulfase antibodies were detected in 31.7% of patients at the end of the study and were related to smaller reduction in urine GAG levels.

It is known that controlled studies in rare diseases are difficult to be conducted and so far only results of observational studies are available or ongoing. Results from two case series studies have been published in recent years. One reports the experience of enzyme replacement therapy with idursulfase in six children under five years old (Alcade-Martín 2010). The children began treatment with a mean age of 3.6 years and were followed for a mean period of nine months. Decreased levels of urinary GAG were observed, also some improvement in the volume of the liver and spleen; in addition, joint mobility stabilized or improved during treatment. Growth rate remained normal as expected; in untreated patients with MPS II, growth decelerates at around age four or five years. With regards to safety, only mild drug-related infusion reactions were noted. The second study assessed overall result of enzyme replacement therapy on the growth of 18 patients (nine under 10 years of age and nine over) followed for more than three years (Schulze-Frenking 2011). All children under 10 years of age (except one who had short stature at baseline) grew at normal rate during this period. Patients over 10 years of age also showed an increase in growth rate in the first two years of treatment, which decreased in the third year. The authors suggested this may be due to puberty. This study indicates that therapy may have a positive effect on growth rate especially when initiated before 10 years of age. In the latest searches undertaken for the update of this review, a further observational study was identified (Jones 2013). The study investigated the effects of enzyme replacement therapy with idursulfase on growth in patients enrolled in the The Hunter Outcome Survey (HOS), a multinational database. A total of 133 patients (8 to 15 years of age at treatment start) with data on height available on more than one occasion within 24 months of treatment start were included. Results showed that the growth velocity after treatment was significantly improved compared with before treatment. Analysis of a covariate showed a significant negative influence on growth of mutation type (patients with deletions or large rearrangements or nonsense mutations) and age (12 to 15 years). Cognitive involvement, pubertal status and functional classification were found not be be related to the growth deficit or response to treatment.

It is noteworthy that in the Schulze-Frenking study one child younger than 10 years of age, who already had short stature at baseline, showed poor response in growth rate with treatment. The study authors suggested that this may be related to the development of antibodies (Schulze-Frenking 2011). The study does not provide more data on safety and the proportion of patients who developed antibodies. From an immunological perspective, the effect of neutralizing antibodies on efficacy is still to be fully evaluated; therefore, no firm conclusions can be drawn about the effect of neutralizing activity on the safety and efficacy of idursulfase.This factor should be carefully evaluated in other studies with long-term follow-up,

While enzyme replacement therapy with idursulfase has been shown to have biologic effects and may improve the functional capacity in patients with MPS II, the clinical significance of these effects is not clear. The treatment improves the distance walked in six minutes (6MWD) but the average improvement is small with wide confidence intervals. Idursulfase has not been shown to improve clinically relevant outcomes such as quality of life, pain, rate of hospitalisation, resources required for home care support and mortality.

Overall completeness and applicability of evidence

The included study provided data on the efficacy and safety of short-term (53 weeks) enzyme replacement therapy with idursulfase for MPS II patients (aged 5 to 31 years). The results of the open-label extension study have recently been published (Muenzer 2011). All patients who completed the double-blinded study received idursulfase 0.5 mg/kg weekly for two years. There were no improvements in the % predicted FVC, only in the absolute FVC, which probably reflected the growth that has occurred in patients younger than 18 years of age during treatment, since this increase was not observed in those aged over 18 years. Increases in the 6MWT remained stable and mean liver and spleen volumes remained reduced. Mean joint range of motion improved only for the shoulder joint. All patients experienced adverse effects, with 59.6% experiencing at least one drug-related adverse effect, 53% an infusion-related adverse effect, 28.7% at least one severe or life-threatening adverse effect. Neutralizing IgG antibodies were detected in 27.1% of the patients at the end of the extension study and seemed to attenuate the improvement in pulmonary function. Patients in the study had to be able to follow instructions and perform the test of the primary endpoint (6MWT and % predicted FVC) which suggests that the patients included were not representative of those with advanced forms of the disease. The drug may achieve improvement of the physical condition, a decrease of organomegaly and urinary excretion of GAGs, but the overall benefit should be evaluated according to global somatic involvement, overall rate of disease progression in CNS and on variables such as improved length of survival.

Quality of the evidence

The quality of the included study was considered good, although we note the absence within the study report of information as to how both the allocation generation and concealment were performed.

Potential biases in the review process

There is concern about selective reporting, due to important clinical outcomes (e.g. growth velocity, left ventricular mass index and overnight apnoea-hypopnoea index not being evaluated in the included study.

Authors' conclusions

Implications for practice

The current evidence is limited. While the randomised clinical trial identified was considered of good quality, it failed to describe important outcomes. It has been demonstrated that enzyme replacement therapy with idursulfase is effective in relation to functional capacity (6MWT and % predicted FVC), liver and spleen volumes and urine GAG excretion in patients with MPS II compared with placebo. There is no available evidence in the included study or in the wider literature on outcomes such as sleep apnoea, cardiac function, quality of life and mortality. More studies are needed to obtain more information on the long-term effectiveness and safety of enzyme replacement therapy.

Implications for research

Further trials, including rigorous multi-domain follow-up of patients receiving treatment, are needed to determine the long-term effects of enzyme replacement therapy. Clinically relevant outcomes should be assessed, such as improvements in cardiac function, respiratory function, including sleep apnoea, stabilization of skeletal abnormality, quality of life, need of hospitalizations and mortality. The effects of immunogenicity on the safety and effectiveness of enzyme replacement therapy with idursulfase need to be better studied.

The effects of enzyme replacement therapy with idursulfase in children under five years of age need to be further investigated, given that the early introduction of therapy with consequent limitation of the formation of lysosomal storage can potentially lead to better outcomes in the evolution of the disease.

Acknowledgements

We would like to thank Tracey Remmington and Nikki Jahnke from the Cochrane Cystic Fibrosis and Genetic Disorders Group for their extensive collaboration.

Data and analyses

Download statistical data

Comparison 1. Idursulfase 0.5 mg/kg versus placebo
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Six-minute walk test (6MWT) (53 weeks)1 Mean Difference (IV, Fixed, 95% CI)Totals not selected
1.1 Idursulfase 0.5 mg/kg weekly1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
1.2 Idursulfase 0.5 mg/kg EOW1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
2 % predicted FVC (53 weeks)1 Mean Difference (IV, Fixed, 95% CI)Totals not selected
2.1 Idursulfase 0.5 mg/kg weekly1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
2.2 Idursulfase 0.5 mg/kg EOW1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
3 Absolute FVC (L) (53 weeks)1 Mean Difference (IV, Fixed, 95% CI)Totals not selected
3.1 Idursulfase 0.5 mg/kg weekly1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
3.2 Idursulfase 0.5 mg/kg EOW1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
4 6MWT+ % predicted FVC (composite score) (53 weeks)1 Mean Difference (Fixed, 95% CI)Totals not selected
4.1 Idursulfase 0.5 mg/kg weekly1 Mean Difference (Fixed, 95% CI)0.0 [0.0, 0.0]
4.2 Idursulfase 0.5 mg/kg EOW1 Mean Difference (Fixed, 95% CI)0.0 [0.0, 0.0]
5 Liver volume (%) (53 weeks)1 Mean Difference (IV, Fixed, 95% CI)Totals not selected
5.1 Idursulfase 0.5 mg/kg weekly1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
5.2 Idursulfase 0.5 mg/kg EOW1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
6 Spleen volume (%) (53 weeks)1 Mean Difference (IV, Fixed, 95% CI)Totals not selected
6.1 Idursulfase 0.5 mg/kg weekly1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
6.2 Idursulfase 0.5 mg/kg EOW1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
7 Urine GAG μg/mg creatinine (%)(53 weeks)1 Mean Difference (IV, Fixed, 95% CI)Totals not selected
7.1 Idursulfase 0.5 mg/kg weekly1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
7.2 Idursulfase 0.5 mg/kg EOW1 Mean Difference (IV, Fixed, 95% CI)0.0 [0.0, 0.0]
8 One or more infusion-related adverse events1 Risk Ratio (M-H, Fixed, 95% CI)Totals not selected
8.1 Idursulfase 0.5 mg/kg weekly1 Risk Ratio (M-H, Fixed, 95% CI)0.0 [0.0, 0.0]
8.2 Idursulfase 0.5 mg/kg EOW1 Risk Ratio (M-H, Fixed, 95% CI)0.0 [0.0, 0.0]
9 Serious adverse events1 Risk Ratio (M-H, Fixed, 95% CI)Totals not selected
9.1 Idursulfase 0.5 mg/kg weekly1 Risk Ratio (M-H, Fixed, 95% CI)0.0 [0.0, 0.0]
9.2 Idursulfase 0.5 mg/kg EOW1 Risk Ratio (M-H, Fixed, 95% CI)0.0 [0.0, 0.0]
Analysis 1.1.

Comparison 1 Idursulfase 0.5 mg/kg versus placebo, Outcome 1 Six-minute walk test (6MWT) (53 weeks).

Analysis 1.2.

Comparison 1 Idursulfase 0.5 mg/kg versus placebo, Outcome 2 % predicted FVC (53 weeks).

Analysis 1.3.

Comparison 1 Idursulfase 0.5 mg/kg versus placebo, Outcome 3 Absolute FVC (L) (53 weeks).

Analysis 1.4.

Comparison 1 Idursulfase 0.5 mg/kg versus placebo, Outcome 4 6MWT+ % predicted FVC (composite score) (53 weeks).

Analysis 1.5.

Comparison 1 Idursulfase 0.5 mg/kg versus placebo, Outcome 5 Liver volume (%) (53 weeks).

Analysis 1.6.

Comparison 1 Idursulfase 0.5 mg/kg versus placebo, Outcome 6 Spleen volume (%) (53 weeks).

Analysis 1.7.

Comparison 1 Idursulfase 0.5 mg/kg versus placebo, Outcome 7 Urine GAG μg/mg creatinine (%)(53 weeks).

Analysis 1.8.

Comparison 1 Idursulfase 0.5 mg/kg versus placebo, Outcome 8 One or more infusion-related adverse events.

Analysis 1.9.

Comparison 1 Idursulfase 0.5 mg/kg versus placebo, Outcome 9 Serious adverse events.

Appendices

Appendix 1. Search strategy - Medline via PubMed

#1 Mucopolysaccharidosis II [mh]

#2 Mucopolysaccharidosis IIs

#3 Mucopolysaccharidoses IIs

#4 Hunter Syndrome Gargoylism

#5 Hunter Syndrome Gargoylisms

#6 Hunter's Syndrome

#7 Hunters Syndrome

#8 Hunter Syndrome

#9 MPSII

#10 MPS II

#11 Mucopolysaccharidosis 2

#12 Mucopolysaccharidoses 2

#13 Mucopolissacaridose II

#14 Mucopolissacaridosis II

#15 #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 OR #9 OR #10 OR #11 OR #12 OR #13 OR #14

#16 Iduronate Sulfatase [Mh]

#17 Sulfoiduronate Sulfatase

#18 Iduronatesulfate Sulfohydrolase

#19 Hunter Corrective Factor

#20 Iduronate Sulfate Sulfatase

#21 Iduronato Sulfatasa

#22  Iduronato Sulfatase

#23 #16 OR #17 OR #18 OR #19 OR #20 OR #21 OR #22

# 24 randomized controlled trial [pt]

# 25 controlled clinical trial [pt]

#26 randomized [tiab]

#27 placebo [tiab]

#28 drug therapy [sh]

#29 randomly [tiab]

#30 trial [tiab]

#31 groups [tiab]

#32 #24 OR #25 OR #26 OR #27 OR #28 OR #29 OR #29 OR #30 OR #31

#33#15 AND #23 AND #32

Appendix 2. Search strategy - LILACS via Bireme

#1 Mucopolysaccharidosis II [mh]

#2 Mucopolysaccharidosis IIs

#3 Mucopolysaccharidoses IIs

#4 Hunter Syndrome Gargoylism

#5 Hunter Syndrome Gargoylisms

#6 Hunter's Syndrome

#7 Hunters Syndrome

#8 Hunter Syndrome

#9 MPSII

#10 MPS II

#11 Mucopolysaccharidosis 2

#12 Mucopolysaccharidoses 2

#13 Mucopolissacaridose II

#14 Mucopolissacaridosis II

#15 #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 OR #9 OR #10 OR #11 OR #12 OR #13 OR #14

#16 Iduronate Sulfatase [Mh]

#17 Sulfoiduronate Sulfatase

#18 Iduronatesulfate Sulfohydrolase

#19 Hunter Corrective Factor

#20 Iduronate Sulfate Sulfatase

#21 Iduronato Sulfatasa

#22  Iduronato Sulfatase

#23 #16 OR #17 OR #18 OR #19 OR #20 OR #21 OR #22

#24 ((Pt RANDOMIZED CONTROLLED TRIAL OR Pt CONTROLLED CLINICAL TRIAL OR Mh RANDOMIZED CONTROLLED TRIALS OR Mh RANDOM ALLOCATION OR Mh DOUBLE-BLIND METHOD OR Mh SINGLE-BLIND METHOD OR Pt MULTICENTER STUDY) OR ((tw ensaio or tw ensayo or tw trial) and (tw azar or tw acaso or tw placebo or tw control$ or tw aleat$ or tw random$ or (tw duplo and tw cego) or (tw doble and tw ciego) or (tw double and tw blind)) and tw clinic$)) AND NOT ((CT ANIMALS OR MH ANIMALS OR CT RABBITS OR CT MICE OR MH RATS OR MH PRIMATES OR MH DOGS OR MH RABBITS OR MH SWINE) AND NOT (CT HUMAN AND CT ANIMALS)) [Palavras]

#25 #15 AND #23 AND #24

Appendix 3. Search strategy - EMBASE via OVID

#1 Mucopolysaccharidosis II [mh]

#2 Mucopolysaccharidosis IIs

#3 Mucopolysaccharidoses IIs

#4 Hunter Syndrome Gargoylism

#5 Hunter Syndrome Gargoylisms

#6 Hunter's Syndrome

#7 Hunters Syndrome

#8 Hunter Syndrome

#9 MPSII

#10 MPS II

#11 Mucopolysaccharidosis 2

#12 Mucopolysaccharidoses 2

#13 Mucopolissacaridose II

#14 Mucopolissacaridosis II

#15 #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 OR #9 OR #10 OR #11 OR #12 OR #13 OR #14

#16 Iduronate Sulfatase [Mh]

#17 Sulfoiduronate Sulfatase

#18 Iduronatesulfate Sulfohydrolase

#19 Hunter Corrective Factor

#20 Iduronate Sulfate Sulfatase

#21 Iduronato Sulfatasa

#22  Iduronato Sulfatase

#23 #16 OR #17 OR #18 OR #19 OR #20 OR #21 OR #22

#24 Controlled study/

#25 Randomization/

#26 Double blind procedure/

#27 Single blind procedure/

#28 Clinical trial/

#29 (clinical adj5 trial$).ti,ab,hw.

#30 ((doubl$ or singl$ or tripl$ or trebl$) adj5 (blind$ or mask$)).ti,ab,hw.

#31Placebo/

#32 Placebo$.ti,ab,hw.

#33 Random$.ti,ab,hw.

#34 Methodology.sh.

#35 latin square.ti,ab,hw.

#36 crossover.ti,ab,hw.

# 37 cross-over.ti,ab,hw.

#38 Crossover Procedure/

#39 Drug comparison/

#40 Comparative study/

#41 (comparative adj5 trial$).ti,ab,hw.

#42 (control$ or prospectiv$ or volunteer$).ti,ab,hw.

#43 exp "Evaluation and Follow Up"/

#44 Prospective study/

#45 or/24-44

#46 animal/ not (human/ and animal/)

#47 45 not 46

#48 #15 OR #23 OR #47

What's new

DateEventDescription
6 November 2013New search has been performedWe carried out new searches but did not identify any eligible trials for inclusion in the review.
6 November 2013New citation required but conclusions have not changedMinor changes have been made throughout the review.

Contributions of authors

Edina Mariko Koga da Silva (EMKS) was responsible for the conception of this review.

EMKS and Regis Bruni Andrioli (RBA) were responsible for developing the search strategy and undertaking searches.

EMKS and Laercio Antonio da Silva (LAS) were responsible for screening search results, organising retrieval of papers, screening retrieved papers against the inclusion criteria, appraising quality of papers and extracting data.

EMKS was responsible for data management for the review and entering data into RevMan. EMKS, LAS and Maria Wany Louzada Strufaldi (MWLS) analysed and interpreted the data. EMKS wrote the results. EMKS, LAS and RBA provided a methodological perspective; and MWLS provided a clinical perspective.

Declarations of interest

None known.

Differences between protocol and review

During the completion of the systematic review we received valuable advice from experts on the definition of the outcomes. It was therefore decided for improve the review and to change the primary outcomes to z score of height and weight and six-minutes walk test (6MWT). For further information, please refer to Types of outcome measures.

Within the Results section of the review the final secondary outcome listed was not pre-defined, although this is a composite score of two pre-defined outcomes. This was regarded as being of clinical interest and appropriate to be included within the review.

Characteristics of studies

Characteristics of included studies [ordered by study ID]

Muenzer 2006

  1. a

    6MWT: 6-minute-walk-test
    AHI: apnoea-hypopnoea index
    ATS: American Thoracic Society
    EOW: every other week
    FVC: forced vital capacity
    JROM: joint range of motion
    I2S: iduronate-2-sulfatase
    LVM: left ventricular mass
    MRI: magnetic resonance imaging

MethodsMulticentre, multinational, double-blind, randomised, placebo-controlled, 53-week clinical trial.
ParticipantsPatients between the ages of 5 and 31 years with a diagnosis of MPS II based on both clinical and biochemical criteria were enrolled in the study. Clinical criteria included having any one of the following MPS II-related abnormalities: hepatosplenomegaly; radiographic evidence of dysostosis multiplex; valvular heart disease; or evidence of obstructive airway disease. The biochemical evidence of MPS II included a documented deficiency in I2S enzyme activity of 10% of the lower limit of the normal range as measured in plasma, fibroblasts, or leukocytes combined with a normal enzyme activity level of another sulfatase. At baseline all patients were required to reproducibly perform pulmonary function testing and have an abnormal FVC of 80% of predicted. Patients who had a tracheostomy or who had received a bone marrow or cord blood transplant were excluded from the study.
InterventionsIntravenous infusions of idursulfase weekly or EOW at a dose of 0.5 mg/kg, or weekly infusions of placebo.
OutcomesThe primary efficacy endpoint in the trial measured changes from baseline to week 53, combining % predicted FVC as a measure of respiratory function and the 6MWT as a measure of functional capacity.The 6MWT was conducted in accordance with ATS guidelines. The secondary efficacy outcome measurements were: passive JROM; liver and spleen volume by MRI; urinary GAG levels and cardiac LVM by echocardiography. All measurements were made at baseline, weeks 18, 36 and 53.
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskWe found no information about generation of randomisation sequence. Patients randomised equally to 1 of 3 treatment arms, randomisation was stratified by age and total disease score at baseline data.
Allocation concealment (selection bias)Unclear riskNot cited.
Blinding (performance bias and detection bias)
All outcomes
Low riskAll patients received intravenous infusion weekly. Patients randomised to EOW idursulfase dosing received placebo infusion during intervening weeks to maintain blinding.
Incomplete outcome data (attrition bias)
All outcomes
Low risk94 (97.9%) of 96 patients completed 1 year of treatment. The two patients who did not complete one year of treatment died during the study: 1 patient in the placebo group and 1 patient in the idursulfase weekly group. Neither death was considered by the investigator to be related to the study drug.
Selective reporting (reporting bias)Unclear riskThere are concern about selective reporting, due important clinical outcomes (e.g. LVM index and overnight AHI) were not evaluated.
Other biasLow riskThe study apparently was free of other problems that could put it at a high risk of bias

Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion
Gutiérrez-Solana 2007Narrative review.
Muenzer 2007Phase I/II clinical trial that evaluated safety and dosing requirements in 12 patients.
Sohn 2013Phase I/II clinical trial comparing a new formulation (idursulfase beta) with the formulation of idursulfase currently available.
Tylki-Szymanska 2008Ongoing case series.

Ancillary