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Keywords:

  • bleeding;
  • desmopressin;
  • FVIII replacement therapy;
  • inhibitor;
  • mild hemophilia A;
  • missense mutations

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Epidemiology
  5. Diagnosis
  6. The natural history of mild hemophilia A
  7. Inhibitor development
  8. Treatment
  9. Conclusions
  10. Disclosure of Conflict of Interests
  11. References

Summary.  Mild hemophilia A (HA), defined by clinical features and factor VIII coagulant activity (FVIII:C) between 0.05 and 0.40 IU mL−1, is characteristically distinct from severe HA. Indeed, although the molecular characterization of mild HA has permitted the identification of specific underlying mutations, its clinical phenotype is strikingly different from that of patients with a severe FVIII defect, where spontaneous hemorrhages or recurrent joint bleeding are usual manifestations. With aging, mild HA patients may develop complications (i.e. cancers and cardiovascular disorders), the management of which may prove challenging due to the concomitant bleeding tendency. Furthermore, the development of inhibitors provides an additional major complication in these patients, because it increases the severity of the bleeding phenotype and complicates their management. Standard management of mild HA includes the use of desmopressin and antifibrinolytic agents for minor bleeding episodes or surgical procedures, whilst major bleeding or surgery requires replacement therapy with FVIII concentrates. As regards treatment of patients with inhibitors, bypassing agents (i.e. activated prothrombin complex concentrates and recombinant activated FVII) have proven effective in the treatment of bleeding episodes, but as there are insufficient data to determine the optimal approach to immune tolerance induction in this group of patients, their optimal management remains controversial. Rituximab is a newer, promising therapeutic option for inhibitor eradication in such patients. Many aspects concerning mild HA remain to be clarified, including the molecular basis, the natural history and the optimal diagnostic and therapeutic strategies. Only large prospective studies will shed light on this condition.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Epidemiology
  5. Diagnosis
  6. The natural history of mild hemophilia A
  7. Inhibitor development
  8. Treatment
  9. Conclusions
  10. Disclosure of Conflict of Interests
  11. References

Hemophilia A (HA) is a rare X-linked recessive bleeding disorder characterized by reduced plasma factor (F) VIII coagulant activity (FVIII:C). The degree of clinical manifestations correlates with the reduction of FVIII:C, and HA is classified as severe (FVIII:C < 0.01 IU mL−1), moderate (0.01–0.05 IU mL−1) or mild (> 0.05–0.40 IU mL−1) forms, according to the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis (ISTH) [1].

Compared with severe hemophilia patients, bleeding episodes in mild hemophilia patients are less frequent and rarely unprovoked or lead to recurrent hemarthrosis and consequent arthropathy [2]. However, in spite of this milder clinical phenotype, a number of largely unresolved issues, such as the response to treatment with desmopressin (DDAVP) and inhibitor development and treatment, have challenged scientists and clinicians over past decades.

In this review, we will focus on the more recent advances in the epidemiology, molecular basis, diagnosis, inhibitor development and treatment of mild hemophilia A.

Epidemiology

  1. Top of page
  2. Abstract
  3. Introduction
  4. Epidemiology
  5. Diagnosis
  6. The natural history of mild hemophilia A
  7. Inhibitor development
  8. Treatment
  9. Conclusions
  10. Disclosure of Conflict of Interests
  11. References

The incidence of hemophilia A (HA) approaches 1 per 5000 male births [3], although estimates related to mild hemophilia vary widely between countries, depending largely on the economic resources available, and interestingly can be correlated to their gross natural product (GNP) [4]. The percentage may therefore approach that of severe hemophilia (34% for mild vs. 43% for severe) in countries with a GNP more than 10 000 US$, while in less developed countries (GNP < 2000 US$) the gap is more evident (18% vs. 50%). In China, where the World Federation of Hemophilia (WFH) started its involvement in 1993 and supported Chinese hemophilia center twinning programs during the last decade, the National Hemophilia Registry recorded 5043 patients, 16% of whom had a mild HA [5]. Recently, Geraghty et al. [6] published a report from 147 hemophilia treatment centers worldwide treating 16 115 HA patients, and 32% had mild or moderate HA, 48% severe HA and 5% had inhibitors. Similar results were reported by the Italian Hemophilia Registry, which included 2679 HA patients, 34% of whom had a mild form (2006 update) [7]. A higher rate of mild HA (51%) was observed by the Canadian Hemophilia Registry among the 1594 HA patients registered [8].

Interestingly, the proportion of patients with mild hemophilia also varies in the same country over time, reflecting improvements in diagnosis, awareness among physicians, and familial investigations (e.g. in a Swedish survey, the apparent rate of mild hemophilia increased from 35% in 1960 to 54% in 1980 [9]). Moreover, different regions in the same country may show different rates, reflecting variability in health care organization and delivery (e.g. the Emilia-Romagna Italian region has developed a web-based registry of inherited bleeding disorders including 610 patients, with a rate of mild HA cases (45%) higher than that reported in the Italian registry [10]).

Diagnosis

  1. Top of page
  2. Abstract
  3. Introduction
  4. Epidemiology
  5. Diagnosis
  6. The natural history of mild hemophilia A
  7. Inhibitor development
  8. Treatment
  9. Conclusions
  10. Disclosure of Conflict of Interests
  11. References

As noted above, spontaneous hemorrhages are very rare in mild HA patients, who are often diagnosed following trauma or a bleeding episode during surgery, or during familial investigations. Bleeding episodes may result in excessive, sometimes life-threatening, hemorrhages [11]; therefore, delays in diagnosis may have harmful consequences. One study involving 55 mild hemophilia patients from two hemophilia centers in the US reported that 64% (35/55) were diagnosed because of a positive family history, while in 27% the diagnosis followed one or more bleeding episodes at a mean age of 5.3 years [11]. The leading hemorrhagic episodes that prompted the diagnosis were hematemesis, soft tissue, mucosal or joint bleeding or prolonged bleeding after procedures such as tonsillectomy, adenoidectomy or dental extractions, whilst in four patients the diagnosis followed abnormal presurgical coagulation screening. A total of 190 bleeding episodes were recorded, most often in muscle or soft tissues (52%), and more rarely involving joints (30%). Trauma triggered the great majority (92%) of bleeding events. In another French study on a cohort of 599 hemophilia patients, the diagnosis was made at a median age of 28.6 months, later than severe and moderate forms (5.8 and 9.0 months, respectively) [12]. Circumstances leading to the diagnosis were, in order of frequency, a bleeding episode (45%), family history (43%) and casualty (12%). Sometimes, the clinical presentation is confusing and leads to misdiagnosis, and in other cases, unusual (e.g. cancer-associated) bleeding may lead to the diagnosis of milder forms of hemophilia [13]. However, patients with mild HA may experience severe bleeds and related complications in spite of the mild coagulation defect not only when the disease is undiagnosed. Indeed, general poor knowledge of bleeding symptoms and therapeutic approaches, together with the lack of familiarity with hemophilia treatment centers and the inability of home treatment, may lead to enormous diagnostic and therapeutic delays with dramatic clinical pictures even in cases of familial or previously diagnosed mild HA. In this context, the role of the comprehensive care provided by specialized hemophilia treatment centers is crucial to improve clinical outcomes and quality of life also for hemophilic patients with a mild defect [14].

A few female carriers of hemophilia may have clotting factor levels in the range of mild hemophilia and may experience an increased bleeding tendency [15]. For example, the proportion of females with mild hemophilia was identified as 10% in one study [11], whereas another compared the bleeding tendency in 135 carriers with that in 25 non-carriers and in an age-matched group of 60 women [16] to show that the carrier group had a significantly higher tendency to bruise, experienced prolonged bleeding from small wounds, and demonstrated a prolonged bleeding tendency after tonsillectomy, tooth extraction, surgery and childbirth. The tendency to bleed was directly correlated with the pre-existing plasma levels of FVIII and FIX. More recently, bleeding tendency was evaluated in 274 carriers and 272 proven non-carriers [17], and the median clotting factor level in carriers was 0.60 IU mL−1 (range 0.05–2.19 IU mL−1) and in non-carriers 1.02 IU mL−1 (range 0.45–3.28 IU mL−1). Despite the broad overlap of FVIII:C levels, carriers of hemophilia bleed more frequently than other women, especially after medical interventions. In addition, decreasing factor levels from 0.60 to 0.05 IU mL−1 were increasingly associated with prolonged bleeding from small wounds and prolonged bleeding after tooth extraction, tonsillectomy and other surgeries.

Laboratory diagnosis

Several coagulation screening tests may be performed for investigation of patients with a bleeding tendency, including a platelet count, an in vivo bleeding time (e.g. Ivy method), an in vitro platelet function analyzer (PFA)-100 test, a prothrombin time (PT), and an activated partial thromboplastin time (aPTT). In mild hemophilia, all of these should be normal with the exception of a possibly prolonged aPTT, dependent on the sensitivity of the test reagents and the residual level of FVIII. However, the aPTT will occasionally be normal, because of several confounders; for example, some reagents lack FVIII sensitivity above 0.30 IU mL−1 [18], and FVIII is an acute phase reactant and may be elevated in these patients on occasion due to inflammatory events. Alternatively, other diagnostic confounders such as liver disease and ABO blood group may complicate the laboratory diagnostic process, inclusive of test results using routine coagulation screening (Fig. 1). Accordingly, whenever there is a clinical suspicion of hemophilia A, even in the absence of a prolonged aPTT, a FVIII:C assay is mandatory. Notably, this is also not without problems. As previously noted, FVIII:C could be falsely elevated due to inflammatory stress-related events [19], and thus yield a normal test result in a clinically affected patient. There is also a considerable overlap in FVIII:C levels between ‘normal individuals’ and those with significant bleeding due to mild deficiencies of FVIII:C [17]. There are also limitations in the tests performed for FVIII:C, including intra-assay, inter-assay and inter-laboratory variation [20], as well as ABO blood group and age-related effects (lower FVIII:C levels with O blood group and increasing levels of FVIII:C with increasing increasing age) [21,22]. This latter phenomenon is interesting and could have relevant therapeutic implications, as it occurs physiologically during aging in healthy individuals and in mild HA, but not in severe/moderate HA. Indeed, should the results of a recent retrospective study [22] be confirmed, substitutive therapy in mild HA patients could be adapted to changing plasma levels at higher age to prevent overdosing and thrombotic risks.

image

Figure 1.  A schematic identifying F8 gene analysis as representing only one part of the complex phenotypic and clinical picture that a patient with mild FVIII deficiency (or mild hemophilia A) may present. For example, von Willebrand factor (VWF) levels and function may influence plasma FVIII level and function, as may the ABO blood group, inflammation or stress events, and so on. Adapted from reference [158].

Download figure to PowerPoint

All these events also mean that clear-cut differentiation between normal individuals and those with mild HA is not always possible. Similar difficulties are evident when attempting to identify female carriers of hemophilia A [17]. There is also some current controversy regarding the differential utility and sensitivity of various assay methods for FVIII, including one-stage, two-stage and chromogenic assays, as well as the role of thrombin generation assessment in this process [23]. Interestingly, differential sensitivity of assay methodologies may have a genetic basis, as discussed below.

Molecular characterization of mild hemophilia A and influence on laboratory diagnosis

To date, more than 200 small deletions or missense mutations have been reported as causing HA [24–26], with missense mutations being most frequently involved [see the Hemophilia A Mutation Structure, Test and Resource Site (HAMSTeRS, http://europium.csc.mrc.ac.uk/)]. Missense mutations accounted for 86% of cases in a study of 101 mostly unrelated patients [27], and 80% of mild HA patients recorded in the Italian Association of Hemophilia Centers (AICE) database [28]. Nevertheless, overall, molecular mechanisms are only partially understood. They may involve sites causing defects in thrombin activation, FVIII synthesis, processing, secretion and stability, von Willebrand factor (VWF) interaction, phospholipids binding and interaction with activated FIX [25]. For example, mutations effecting Arg residues located at the thrombin cleavage sites result in mild/moderate HA, whereas substitution of the Arg372 impairs thrombin cleavage of the heavy chain [29], and substitution of Arg1689 prevents cleavage of the FVIII light chain [30]. Interestingly, the mutation Tyr346Cys, responsible for a delayed thrombin activation, has been described in patients with FVIII:C levels that are more reduced in one-stage than in two-stage clotting or chromogenic assays [31,32]. This discrepancy has been attributed to the prolonged incubation time with thrombin during the first phase of the latter assays, allowing better FVIII activation [32]. However, as this mutation has also been observed in patients without a clinical bleeding phenotype, it may represent a laboratory finding rather than a relevant bleeding disorder [33]. A similar discrepancy (higher FVIII:C in the two-stage assay) is also observed with two other mutations, Glu321Lys and Glu720Lys. The former is located in close proximity to the thrombin cleavage site Arg372 [34], whereas the latter is adjacent to a binding site of activated FIX in the A2 domain and could result in a reduced affinity for activated FIX [35]. However, the opposite discrepancy (reduced FVIII:C in two-stage compared with one-stage assay) is more frequently observed in mild HA patients [24]. Since 1996, at least 20 different missense mutations have been identified in families with discrepant hemophilia [36–45], most located in regions at the interface between A1-A2, A1-A3 and A2-A3 domains. The stabilizing role of these regions is crucial for the appropriate function of the activated FVIII. Thus, it is likely that these mutations influence FVIII stability, promoting faster inactivation. Unfortunately, some patients may have a mutation that exhibits a normal FVIII activity by one-stage assay and as a consequence the correct diagnosis may be missed through routine screening evaluations [36]. In order to overcome the discrepancy between coagulation assays, some investigators have recently proposed the use of a thrombin generation assay to assess the bleeding tendency in mild hemophilia patients [23].

A number of missense mutations have also been identified within the C1 (Gln2087Glu, Arg2090Cys, Arg2150Cys/His, Arg2159Cys, Arg2163Cys, Ile2098Ser, Asn2129Ser, Ser2119Tyr, Pro2153Gln) and C2 (Arg2304/Cys/Gly, Arg2307Thr, Pro2300Leu) domains, which play a key role in FVIII binding to VWF, and may act by either altering the core structures of these domains or disrupting the surface sites of FVIII-VWF interaction [46,47]. In particular, analysis of the binding of recombinant Arg2150His, Ile2098Ser and Ser2119Tyr and normal FVIII to VWF indicated that the affinities of the mutants were 3-, 8- and 80-fold lower, respectively, than that of normal FVIII [42]. Similarly, substitutions affecting the residue Tyr1680 in the A3 domain are associated with mild hemophilia as they prevent a sulfation critical for FVIII binding to VWF and reduce by 5-fold the affinity of the mutated FVIII for VWF [48].

Nevertheless, by currently available mutational analyses, the causative genetic event remains undetected in many patients with hemophilia, including those with mild hemophilia and this may thus contribute to ongoing diagnostic uncertainties.

Molecular genetic testing in females

Several mechanisms may be responsible for a hemophilic phenotype in women [49], including homozygous mutations through consanguineous relationships, compound heterozygous mutations, and heterozygous mutations combined with non-random inactivation of the X-chromosome. Indeed, while usually about half of each of the X-chromosomes is inactivated, in some cases more healthy X-chromosomes may be inactivated, significantly affecting the FVIII production of the normal allele and inducing a laboratory and clinical phenotype similar to mild hemophilia. Also, molecular genetic testing for female hemophilia carriers is complicated by the presence of a second normal allele that may mask the presence of a genetic abnormality [50]. Interestingly, the type of mutation present in hemophilia carriers may not contribute to the level of apparent FVIII:C detected in these women, which can instead be correlated to other parameters, including ABO blood group, pregnancy and stress [51].

Hemophilia A or type 2N von Willebrand disease?

In the diagnostic investigation of patients with mild bleeding, mild HA has to be differentiated from von Willebrand disease (VWD), particularly type 2N, which is characterized by a similar phenotype and clinical picture [52–54], but instead due to an intrinsic abnormality of VWF leading to a decreased plasma half-life of FVIII. Other differences between mild HA and type 2N VWD include the pattern of inheritance (X-linked for mild HA and autosomal recessive for type 2N VWD) and results for the VWF:FVIII binding assay (normal in mild HA and reduced in type 2N VWD). Indeed, this assay represents the discriminatory laboratory procedure, although the respective analysis of FVIII and VWF gene mutations may further help to differentiate the two disorders [55,56].

The natural history of mild hemophilia A

  1. Top of page
  2. Abstract
  3. Introduction
  4. Epidemiology
  5. Diagnosis
  6. The natural history of mild hemophilia A
  7. Inhibitor development
  8. Treatment
  9. Conclusions
  10. Disclosure of Conflict of Interests
  11. References

The course of mild HA is obviously less dramatic than that of severe forms. The life expectancy of patients with mild HA has significantly increased during the last decades, progressively approaching that of the normal population, due to progress in replacement therapy and expanding global care by hemophilia centers [57,58]. From 1900 to 1942, the life expectancy among severe hemophilia patients in Sweden was 16.5 years, in contrast to 29 years for those with mild disease [59]. In a UK survey conducted between 1943 and 1957, patients with severe disease lived to 23.2 years while those with mild disease lived to 50 years [60]. During the period of 1960–1980, the life expectancy was 72 years for Swedish patients with mild hemophilia, compared with 75.5 years in the normal population [61]. A normal cumulative relative survival (0.986; 95% CI 0.858–1.082) was observed in mild/moderate Austrian hemophilia patients during the period 1983–2006 [62]. The severity of the hemophilia has emerged as an independent risk factor for mortality in a number of studies [63]. In a multicenter study involving hemophilia centers from the USA and Europe, patients with moderate and severe coagulopathy had approximately 2- and 3-fold higher mortality rates than patients with mild coagulopathy [64]. In another study conducted in the Dutch hemophilia population, the mortality rate for patients with severe hemophilia during the period 1986–1992 was four times higher than that of patients with mild hemophilia, who had a standardized mortality ratio (SMR) (1.1; 95% CI 0.6–1.8) and a life expectancy (74 years) similar to that of the general Dutch male population [65].

This positive survival trend over the decades was dramatically interrupted by the emerging transfusion-transmitted viral infections [i.e. human immunodeficiency virus (HIV) and hepatitis C virus (HCV)]. For example, in the UK, the death rate of mild/moderate hemophilia during the period 1977–1984 was 4 per 1000 and unfortunately increased to 85 per 1000 in HIV-seropositive patients in 1991–1992 [66]. Likewise, in a Greek study over the period 1972–1993, the SMR in mild hemophiliacs was 0.9, but increased to 11.4 in those who were infected with HIV [67]. However, although these viruses infected all forms of hemophilia patients, this phenomenon was less evident for those with mild hemophilia, probably due to the reduced frequency of required treatment with blood products and thereby the reduced risk of exposure to viral infections [68–70]. Interestingly, a very low incidence of HIV infection (2.9%) was recorded in Italian mild HA patients compared with other countries, probably because of Italy’s more conservative therapeutic approach and more widespread use of alternative therapies, such as DDAVP [71].

Nevertheless, HIV and HCV infection remained the leading causes of death during the last two decades even in the mild hemophilia population [62,68–70]. However, excluding individuals infected with HIV and HCV, life expectancy of patients with mild hemophilia approached that of the general male population. In a prospective study in Dutch hemophiliacs during the decade 1992–2001 [70], the life expectancy at birth of patients with mild hemophilia was lower than that of the male population (73 vs. 76 years), but after censoring deaths because of viral infections, the life expectancy of mild hemophilia patients increased to 75 years. Similarly, in a study conducted on Canadian hemophiliacs during the years 1980–1995 [72], the median life expectancy in HIV-positive mild hemophilia patients was 47 years vs. 85 years in those who were HIV negative.

Only a few studies to date have analyzed the causes of mortality in the hemophilia population after excluding those related to HIV and HCV infections. Interestingly, there is increasing evidence that hemophilia might be protective against cardiovascular disease [73–77]. Plug et al. [70] reported a reduced rate of mortality for ischemic heart disease (SMR 0.5), although a sub-analysis according to hemophilia severity was not performed. In a UK study, an identical reduction in mortality rate was reported among hemophiliacs with severe and mild/moderate disease (38% and 37%, respectively) [78], and a similar rate of reduction (36%) was observed in a study of mortality from ischemic heart disease among carriers of hemophilia [79]. Conversely, an increased rate of ischemic heart disease was observed by Kulkarni et al. [80] in mild hemophilia patients as compared with moderate and severe hemophilia (3.4%, 0.7% and 0.4%, respectively). Likewise, Walsh et al. [81] reported a higher incidence of heart disease compared with a control group (18% and 9%, respectively).

The supposed lower incidence of ischemic heart disease in hemophiliacs has been attributed to their hypocoagulable state, which might provide a protective milieu for the development of atherosclerosis [75]. Although a murine model of severe hemophilia showed reduced early-stage atherosclerotic lesions [82], studies on humans using ultrasound evaluation of intima-media thickness (a well-known method for the assessment of initial atherosclerosis) of several arterial districts yielded conflicting results in hemophiliacs [83–86]. Nevertheless, a number of reports on cardiovascular events in hemophiliacs have now been published. Girolami et al. [87] reviewed the literature and reported 42 cases of thrombotic cardiovascular events until 2005 in patients with HA, mostly occurring after infusion of FVIII concentrates, activated prothrombin complex concentrates (APCC), recombinant activated factor VII (rFVIIa) or DDAVP. Eleven of 36 myocardial infarctions occurred in patients with mild HA, with seven related to treatment (two FVIII concentrate, two PCC, three DDAVP). In another study [88], five of seven HA patients with coronary artery disease undergoing cardiac surgery or catheterization had a mild coagulation defect. Nevertheless, cardiovascular complications in hemophilia patients appear to be increasing, probably due to aging of the hemophilia population, and will represent a major challenge for future physicians. Indeed, their appropriate management requires a close cooperation between hemophilia specialists, cardiologists, nursing staff and laboratory professionals. In order to provide a useful tool for the treatment of ischemic heart disease in hemophilia patients, clinical guidelines have been recently implemented [89], albeit institutionally based and primarily built on expert opinion given the paucity of good studies.

With the exception of HCV-associated hepatocellular carcinomas and HIV-associated lymphomas, mortality rates for cancer in mild hemophilia patients seem the same as in the general population [72]. Indeed, the in vitro and in vivo findings that severe hemophilia protects against cancer development have not been confirmed for mild hemophilia [90]. For example, in one study including 6018 HIV-uninfected hemophiliacs that died during the period 1977–1998, a progressive reduction of cancer incidence was observed with increasing severity of hemophilia [78]. Indeed, while the SMR for neoplasms different from liver cancers or lymphomas was 0.95 in patients with mild/moderate hemophilia, it decreased to 0.65 in patients with severe hemophilia. Thus, with increasing age, mild hemophilia patients might develop malignancies that require surgical and/or chemotherapeutic approaches, and although hemophilia is not a contraindication for the treatment of cancer, it may increase the potential risk of bleeding associated with some invasive diagnostic procedures. These should therefore be performed only under adequate replacement therapy and in close collaboration with hemophilia specialists. On the other hand, the chemotherapy-induced blood cell or mucosal toxicity or hemostatic disturbances may hinder the completion or require a dose reduction of anti-cancer treatments [91].

Inhibitor development

  1. Top of page
  2. Abstract
  3. Introduction
  4. Epidemiology
  5. Diagnosis
  6. The natural history of mild hemophilia A
  7. Inhibitor development
  8. Treatment
  9. Conclusions
  10. Disclosure of Conflict of Interests
  11. References

Inhibitors against FVIII are a major problem in the treatment of patients with hemophilia. Although such inhibitors are most frequently seen in patients with severe hemophilia [92,93], the development of antibodies against FVIII in mild HA can cause considerable clinical problems because the inhibitor, directed against both endogenous and exogenous FVIII, usually changes the bleeding phenotype from a mild to severe form [94]. The epidemiologic, pathogenic, clinical and therapeutic features of inhibitors in mild/moderate HA patients are distinct from those arising in patients with severe HA [92,93,95,96].

The overall incidence of inhibitors in mild hemophilia has been estimated to be between 3% and 13%, based on available data [97–99]. In a prospective study of inhibitor incidence among 1306 US HA patients, only 6% of those with inhibitors had basal FVIII levels higher than 0.03 IU mL−1 [100]. Conversely, the UK Haemophilia Centre Doctors’ Organization, reporting on the incidence of new inhibitors over the period 1990–1997, showed that 15 (28%) of the 57 cases of new inhibitor development occurred in patients with a mild or moderate defect [101].

Both type I and II reaction-kinetic inhibitors have been reported in patients with mild HA, [102,103], although type II seem more frequent. This is in contrast to inhibitors in patients with severe HA, where type I are more frequently described [95]. In most cases, inhibitors in mild hemophilia are characterized by a high titer [101,104], and occur more frequently later in life (during the second-third decade of life) than in severely affected hemophiliacs, probably because the former rarely require treatment with FVIII concentrates during their youth because they do not bleed spontaneously [101].

The presence of an inhibitor in mild HA must be suspected if these patients develop a bleeding pattern similar to that of severe HA, such as severe spontaneous bleeding, especially in joints and muscles [105]. However, the bleeding may sometimes resemble that observed in acquired hemophilia, with a predominance of large cutaneous and mucosal bleeding, particularly in gastrointestinal and urogenital tracts [101]. The change in the bleeding pattern is explained by the cross-reactivity of the inhibitor with endogenous FVIII, resulting in a residual FVIII:C level < 0.01 IU mL−1 [25].

Both genetic and environmental factors are known to be involved in inhibitor development [93,96]. For example, in the Malmö International Brother Study (MIBS), an international study of 164 siblings with mild, moderate and severe HA, the inhibitor risk in patients with a positive family history of inhibitors was higher than that of those without a family member with an inhibitor, inclusive of those with mild hemophilia [106]. The existence of a genetic predisposition to the development of inhibitors in patients with mild HA is closely linked to the type of FVIII gene mutation [95]. Indeed, some specific missense mutations, mostly located within the C1 and C2 domains of the light chain and within the A2 domain of the heavy chain of the FVIII molecule, are associated with an unexpectedly high incidence of inhibitors. This is the case for Tyr2105Cys, Arg2150Hys, Arg593Cys and Trp2229Cys mutations [47,101,107–117], which, according to the HAMSTeRS database (accessed July 2009), were associated with inhibitor development in 44% (4/9), 24% (15/63), 12% (6/51) and 40% (8/20) of the cases, respectively. In the series reported by Hay et al. [101], 7/9 of the different missense mutations described were clustered in a restricted region within 100 bases of the junction between the C1 and C2 domains of the light chain of the FVIII molecule. In addition, 9/16 genotyped patients with mild/moderate HA carried missense mutations introducing a new Cys residue (Tyr2105Cys, Trp2229Cys and Arg593Cys), which may affect the formation of disulphide bridges leading to stable abnormal conformations. These mutations may give rise to conformational changes in the FVIII molecule, becoming antigenically distinct from ‘wild-type’ FVIII. Thus, infused FVIII is recognized as non-self and results in inhibitor production, which in turn neutralizes in most cases normal infused FVIII and also cross-reacts with the patient’s own mutant FVIII [101].

Non-genetic risk factors for developing inhibitors in mild/moderate HA may potentially include the type of clotting factor concentrate used for treatment, the modality of administration, and switching between products [93,118]. However, inhibitor formation has been reported in patients receiving a large variety of plasma-derived or recombinant FVIII concentrates, and none of them appeared clearly associated with a higher rate of inhibitor development [95]. In many cases of inhibitors in mild HA, an episode of intense treatment with FVIII concentrates precedes the antibody development [119,120]. In one series [105], about two-thirds of the inhibitors (16/26) were detected after intensive replacement therapy for surgery or trauma, although no particular concentrate was implicated. The intensity of exposure to FVIII concentrates as a risk factor for inhibitor development has also been reported [121], with the overall incidence of inhibitors in 54 patients with mild HA (7.4%) increasing to 25% (4/16) when the analysis was restricted to patients with an intensive exposure (at least 6 consecutive days) to FVIII concentrates. Because four out of seven (57%) patients receiving FVIII concentrates by continuous infusion developed inhibitors, this modality of administration was suggested to confer a higher risk of inhibitor development than repeated bolus infusions. Likewise, in a retrospective study conducted in 13 German hemophilia centers [122], 5/10 patients who developed an inhibitor after continuous infusion had mild/moderate HA. Other reports have confirmed these findings [104,123]. Finally, Eckhardt et al. [124] collected data from 138 mild/moderate HA patients over a 28-year period, to identify that the intensive perioperative use of FVIII concentrate, especially when administered by continuous infusion, along with the Arg593Cys mutation, was associated with a higher risk of inhibitor development. However, these data were obtained from retrospective studies and prospective trials are required to definitely address the issue of the relationship between FVIII replacement therapy and inhibitor development.

Laboratory issues related to inhibitor detection

In brief, inhibitors may initially be detected by mixing studies employing routine coagulation tests [125]. However, their characterization requires performance of specific assays such as the classical Bethesda assay [126] or the Nijmegen modification [127]. Like the case for diagnosis of HA noted above, laboratory assessment of inhibitors is also problematic, with a significant rate (∼15%) of false positive and false negative inhibitor identification, as well as high inter-laboratory variation evidenced in recent cross-laboratory studies [128].

Treatment

  1. Top of page
  2. Abstract
  3. Introduction
  4. Epidemiology
  5. Diagnosis
  6. The natural history of mild hemophilia A
  7. Inhibitor development
  8. Treatment
  9. Conclusions
  10. Disclosure of Conflict of Interests
  11. References

A variety of therapeutic tools are available for the management of patients with mild HA, the choice of which depends on the FVIII basal levels, the type of bleeding and surgical/invasive procedure and whether or not an inhibitor is present. Table 1 summarizes the therapeutic options for mild HA.

Table 1.   Treatment options for mild hemophilia A patients
  1. s.c., subcutaneously; i.v., intravenously; P.O., orally; TD, thrice daily; DDAVP, desmopressin; APCC, activated prothrombin complex concentrates; rFVIIa, recombinant activated FVII; ITI, induction of immune tolerance.

(1) Minor bleeding episodes/minor surgical procedures
 DDAVP: 0.3 μg kg−1 s.c. or i.v., eventually repeated every 8–12-h.
 Tranexamic acid: 20 mg kg−1 TD−1 P.O. or 10 mg kg−1 TD−1 i.v. alone or in association with DDAVP.
(2) Major bleeding episodes/major surgical procedures
 FVIII concentrates: dosages should be calculated to reach a desired FVIII initial level of 80–100% for 1–7 days and a maintenance level of 50% for 7–14 days.
(3) Inhibitors
  Treatment or prevention of bleeding: DDAVP (0.3 μg kg−1 s.c. or i.v.) if FVIII:C levels are measurable, APCC (50 IU kg−1 i.v. every 8–12 h), rFVIIa (90 μg kg−1 i.v. every 2–3 h).
 Inhibitor eradication: ITI, immunosuppressive agents (steroids, cyclophosphamide, rituximab)

DDAVP and antifibrinolytic agents

DDAVP has been successfully used for 25 years in patients with mild HA to prevent or treat bleeding episodes [129–134]. However, its clinical usefulness is highly correlated with the post-infusion plasma levels of FVIII, which in turn depend on the patient’s basal FVIII [134]. Consequently, mild HA patients should be tested with DDAVP prior to therapeutic use [134,135]. This is particularly true for children where a lower response rate to DDAVP may be evident when compared with adults [136,137]. It is generally agreed that a FVIII post-infusion level of at least 0.30 IU mL−1 should be sufficient for the treatment of minor bleedings or for minor surgery, such as dental extractions. On the other hand, a level > 0.50 IU mL−1 post-administration is required for treatment of major surgery. Unfortunately, repeated administrations of DDAVP over a short time may induce tachyphylaxis and hamper its clinical efficacy [129]. The optimal dose of DDAVP to achieve maximum FVIII response is 0.3 μg kg−1 intravenously, giving a three to five times increase of FVIII levels over baseline around 1 h after completion of the infusion, with the circulating FVIII half-life being around 5–8 h. Doses can be repeated at 8- to 24-h intervals if needed, though tachyphylaxis will occur, and a single dose may be sufficient for the management of minor surgical interventions [134]. Subcutaneous injection at the same dose (0.3 μg kg−1) produces a similar, although slower, response to that seen with intravenous infusion. Intra-nasal DDAVP can also be used, although this product is not available in all countries [138]. DDAVP usage has few, self-limited, minor side-effects, including facial flush, headache, a small decrease in blood pressure and an increase in heart rate [130]. Furthermore, the drug should be administered very cautiously in young children due to their increased risk of hyponatremia [139]. There are some concerns regarding the use of DDAVP in pregnant symptomatic HA carriers as it may cause placental insufficiency because of vasoconstriction, miscarriage due to an oxytocic effect and maternal/neonatal hyponatremia [140]. However, the results of a recent survey by Mannucci [141] on the use of DDAVP in 32 pregnant FVIII-deficient women suggested that DDAVP could be safely used during the first two trimesters of pregnancy.

Castaman et al. [142] prospectively investigated the relationship between biologic response to DDAVP and F8 mutations in 50 mild HA patients. Interestingly, eight out of nine patients without detectable causative F8 mutations did not respond to DDAVP. In addition, we have recently characterized a family group carrying a novel mutation in the F8 promoter region, resulting in mild HA associated with a lack of response to DDAVP [143]. Overall, these findings suggest that, similarly to type 1 VWD [144], the response to DDAVP of mild HA might be at least partially genetically determined. DDAVP should also be used whenever possible, alone or in association with FVIII concentrates, in order to minimize the exposure to exogenous FVIII, in those at particularly high risk of developing inhibitors (e.g. carrying specific missense mutations and undergoing surgical procedures) [145,146].

Antifibrinolytic treatment (i.e. tranexamic acid) is particularly effective, alone or in association with DDAVP, in mucosal hemorrhages, with the exception of hematuria, where it may provoke obstruction of the urinary tract [147]. The recommended dose is 10 mg kg−1 intravenously or 20 mg kg−1 orally every 8 h [148]. Tranexamic acid given topically as mouthwashes, at a dose of 1 g every 6 h for 5 days, is also effective for the prevention of bleeding in hemophiliacs undergoing oral surgery [149].

FVIII replacement therapy

Although DDAVP has been successfully used in mild HA patients undergoing major surgery [144], the administration of FVIII concentrates is typically the treatment of choice here because the desired FVIII target levels can be reached without tachyphylaxis, the major limitation of DDAVP. The therapeutic approach is the same as for patients with severe hemophilia with identical target levels and frequency of administration (Table 1), although obviously, the dose required to reach these targets correlates inversely with the patient’s basal FVIII levels.

Although current plasma-derived FVIII concentrates are considered safe products, according to the several treatment guidelines of hemophilia [148,150], recombinant FVIII products are currently recommended in patients with congenital HA, especially if they have never been exposed to plasma products, because of the theoretically reduced risk of transmission of infectious agents.

Monitoring of therapy

In general, the same test used to diagnose HA (i.e. FVIII:C) is used to monitor therapy. As is the case for HA identification, there is some controversy regarding the differential utility of different assays, particularly with respect to recombinant products and the use of the chromogenic FVIII assay [151].

Management of patients with inhibitors

Bleeding episodes in patients with mild/moderate hemophilia and inhibitors are usually treated with bypassing agents, such as APCC or rFVIIa [152,153]. Some patients with inhibitors, especially those with basal measurable FVIII levels, can be treated successfully with DDAVP as the antibody may or may not inhibit endogenous FVIII to the same extent as exogenous FVIII [138]. In one series [101], eight patients with adequate circulating FVIII levels were successfully treated with DDAVP. The effective prophylactic use of DDAVP and rFVIIa in such patients in order to restore a mild bleeding phenotype and to avoid exposure to exogenous FVIII has also been reported [152].

A variety of therapeutic options for the eradication of the inhibitors in mild HA patients are available, including immune tolerance induction (ITI) and immunomodulatory agents (e.g. corticosteroids, cyclophosphamide, and the anti CD-20 monoclonal antibody rituximab) [95]. In the series reported by Hay et al. [101], various ITI regimens (Malmö, Bonn and Van Creveld protocol) were attempted in eight patients with a complete or partial response in six of them. Other reports have described the successful use of immunosuppressive therapy in such patients [154].

After the first report by Wiestner et al. [155], showing a rapid response of FVIII inhibitor to an immunosuppressive regimen including prednisone and rituximab in a patient with mild HA, a number of case reports have further documented the efficacy of this promising agent in these patients [156]. A meta-analysis of the effectiveness of rituximab in patients with congenital hemophilia and inhibitors has recently been published by our group [157]. Among the 44 evaluable cases collected from the literature, an unexpectedly high rate of complete responses was observed in patients with mild/moderate hemophilia as compared with those with severe hemophilia [12/16 (75%) vs. 12/28 (42.9%); = 0.02]. If confirmed by prospective studies using larger populations, these interesting findings might offer an important chance of cure in mild HA patients with inhibitors.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Epidemiology
  5. Diagnosis
  6. The natural history of mild hemophilia A
  7. Inhibitor development
  8. Treatment
  9. Conclusions
  10. Disclosure of Conflict of Interests
  11. References

Mild HA is an inherited bleeding disorder with pathogenic, clinical and therapeutic characteristics clearly distinguished from more severe forms. Although the clinical bleeding phenotype is less dramatic than that of severe HA, its management may be equally challenging for physicians. This is the case for post-surgical bleeding in patients with unrecognized mild hemophilia or where severe bleeding phenotypes with a mild defect exist but with high titer inhibitors. The diagnosis of mild HA remains challenging given inter-patient variability and the limitations associated with laboratory testing. The investigation of patients with inhibitors is similarly challenging. The natural history of mild hemophilia is poorly understood and further prospective studies on large patient populations are needed to improve our knowledge of this condition and its associated co-morbidities. Parallel improvements in the molecular characterization of this disorder will help us to elucidate the pathogenic underlying mechanisms with the aim of improving outcomes and quality of life in these patients through the identification of personalized tailored treatments.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Epidemiology
  5. Diagnosis
  6. The natural history of mild hemophilia A
  7. Inhibitor development
  8. Treatment
  9. Conclusions
  10. Disclosure of Conflict of Interests
  11. References
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