Severe neuromuscular forms of glycogen storage disease type IV: Histological, clinical, biochemical, and molecular findings in a large French case series

Glycogen storage disease type IV (GSD IV), also called Andersen disease, or amylopectinosis, is a highly heterogeneous autosomal recessive disorder caused by a glycogen branching enzyme (GBE, 1,4‐alpha‐glucan branching enzyme) deficiency secondary to pathogenic variants on GBE1 gene. The incidence is evaluated to 1:600 000 to 1:800 000 of live births. GBE deficiency leads to an excessive deposition of structurally abnormal, amylopectin‐like glycogen in affected tissues (liver, skeletal muscle, heart, nervous system, etc.). Diagnosis is often guided by histological findings and confirmed by GBE activity deficiency and molecular studies. Severe neuromuscular forms of GSD IV are very rare and of disastrous prognosis. Identification and characterization of these forms are important for genetic counseling for further pregnancies. Here we describe clinical, histological, enzymatic, and molecular findings of 10 cases from 8 families, the largest case series reported so far, of severe neuromuscular forms of GSD IV along with a literature review. Main antenatal features are: fetal akinesia deformation sequence or arthrogryposis/joint contractures often associated with muscle atrophy, decreased fetal movement, cystic hygroma, and/or hydrops fetalis. If pregnancy is carried to term, the main clinical features observed at birth are severe hypotonia and/or muscle atrophy, with the need for mechanical ventilation, cardiomyopathy, retrognathism, and arthrogryposis. All our patients were stillborn or died within 1 month of life. In addition, we identified five novel GBE1 variants.

nervous system, etc.).Diagnosis is often guided by histological findings and confirmed by GBE activity deficiency and molecular studies.Severe neuromuscular forms of GSD IV are very rare and of disastrous prognosis.Identification and characterization of these forms are important for genetic counseling for further pregnancies.Here we describe clinical, histological, enzymatic, and molecular findings of 10 cases from 8 families, the largest case series reported so far, of severe neuromuscular forms of GSD IV along with a literature review.Main antenatal features are: fetal akinesia deformation sequence or arthrogryposis/joint contractures often associated with muscle atrophy, decreased fetal movement, cystic hygroma, and/or hydrops fetalis.If pregnancy is carried to term, the main clinical features observed at birth are severe hypotonia and/or muscle atrophy, with the need for mechanical ventilation, cardiomyopathy, retrognathism, and arthrogryposis.All our patients were stillborn or died within 1 month of life.In addition, we identified five novel GBE1 variants.
Roseline Froissart and Magali Pettazzoni contributed equally to this work.

| INTRODUCTION
Glycogenosis type IV (GSD IV, OMIM: #232500) or Andersen's disease is a rare autosomal recessive metabolic disorder caused by pathogenic variants in the GBE1 gene located on chromosome 3p12.2.This leads to glycogen branching enzyme (GBE, 1,4-alpha-glucan-branching enzyme 1; EC 2.4.1.18)deficiency.It results in the accumulation of an amylopectine-like polysaccharide, which is less soluble than normal branched glycogen, in several tissues, including muscle, heart, liver, or the nervous system.This abnormal accumulation can be detected on histological examination with characteristic cytoplasmic inclusions in cells that are stained by periodic acid schiff (PAS) and partially resistant to diastase digestion.When observed, this accumulation may contribute to the diagnosis.The incidence of this disease is estimated from 1:600 000 to 1:800 000 live births 1 and accounts for about 3% of all GSD. 2 GSD IV is a phenotypic continuum with a broad heterogeneity in the age of onset, the clinical spectrum, the severity of the affected tissues, making the diagnosis difficult to establish.Historically, six clinical subtypes of GSD IV were distinguished, depending on the clinical presentation (hepatic, neuromuscular, or both), the age of onset and the severity. 3,4In particular, severe neuromuscular presentations were either classified as the fatal perinatal subtype, with hydrops fetalis, joint contractures, and perinatal death or as the congenital/ neonatal subtype, presenting at birth with severe hypotonia, muscle atrophy, with the need for mechanical ventilation and death in the neonatal period or in early infancy.The use of this subtype system was flawed given the degree of phenotypic heterogeneity of this disease, the overlap in clinical features and the lack of clear prognosis.Kiely and colleagues recently proposed a more accurate conceptualization of GSD IV as a multidimensional clinical continuum, based on a phenotypic characterization score scaling the neuromuscular, hepatic, and cardiac involvement. 3Following this novel approach, we present clinical, histological, biochemical, and molecular findings of 10 unpublished cases of severe neuromuscular GSD IV diagnosed in our laboratory (Biochemistry and Molecular Biology Department, Lyon, France).Three other cases from our laboratory that have been previously published are not included in this series (one case referred to as 'congenital case' 5 ) and two cases referred to as 'perinatal cases' 6,7 ).This work represents the largest GSD IV case series description to our knowledge.We compared our findings to all the available cases described in the literature to highlight the most frequent clinical and histological features of these forms.

| METHODS
Retrospective clinical, biological, histological, and molecular data of unpublished cases of severe neuromuscular GSD IV diagnosed in our laboratory were collected.GBE enzyme activity was determined according to the method described by Brown and Brown. 8GBE1 gene analysis was performed by Sanger sequencing, and for the most recent cases, by next generation sequencing (NextSeq 500 Illumina ® , San Diego, CA, USA).Written consent was obtained for all cases.All histological samples were reviewed and PAS and PAS diastase staining were systematically performed on the liver, muscle, heart, brain, and placenta when available.

| Case series description
We report 10 severe neuromuscular cases from eight different families.Clinical, biological, histological, and molecular data are summarized in Table 1.

| Patients 1 and 2 (siblings)
An infant girl, stillborn at 34 weeks of gestation (WG), was the first child of consanguineous Turkish parents (Patient 1).The pregnancy was marked by significant polyhydramnios and threatened preterm labor at 32 WG.At birth, the child presented with growth retardation, fetal akinesia deformation sequence (FADS), facial dysmorphism (retrognathism), muscle atrophy, and pulmonary hypoplasia.The second child, born 2 years later, was healthy.The third pregnancy (Patient 2) was marked by polyhydramnios at 31 WG and facial dysmorphism (retrognathism).The mother gave spontaneous preterm birth at 33.4 WG to a male child who displayed no respiratory movement and died within the first minutes after birth.The histological analysis of muscle biopsy in T A B L E 1 Clinical, histological and biological data of 10 cases of severe neuromuscular GSD IV.  (Continues)  Patient 2 identified intracytoplasmic pale yellow groundglass inclusions on hematoxylin eosin saffron (HES), which harbored a Maltese cross pattern on polarization.These inclusions were stained with PAS and partially resistant to diastase digestion.Similar inclusions were also observed in the heart and liver.Ultrastructural analysis of the muscle showed granular-filamentous inclusions.These findings were characteristic of GSD IV.The retrospective analysis of the muscle biopsy of Patient 1 identified the same findings.Unfortunately, GBE activity measurement was not possible because of poor storage conditions of liver and muscle biopsies collected postmortem.However, it could be performed in fibroblasts from both parents (skin biopsy) and showed decreased activity compared to the day control.GBE1 gene analysis identified a variant at heterozygous state in both parents in exon 13 (c.1643G>T;p.Trp548Leu).After the third pregnancy, the mother had a miscarriage.For the fifth and sixth pregnancies, prenatal diagnosis using enzymatic activity assay in chorionic cultured cells was found to be normal for both.Later, GBE1 studies allowed the determination that both the seventh and eighth fetuses were affected, and medical abortion was performed.

| Patients 3 and 4 (siblings)
Patient 3, a male, was the first child of consanguineous Turkish parents.The pregnancy was uneventful until the end of the third trimester, when reduced fetal movements were noticed.Ultrasonography performed after the expected term revealed akinesia and polyhydramnios.A cesarean section was performed at 39 WG + 5 days.Shortly after birth, the neonate was intubated and required respiratory support.He presented with macrosomia, facial dysmorphism (frontal bossing, hirsutism, and ogival palate), pectus excavatum, joint stiffness and contractures (arthrogryposis), syndactyly and adductus thumb, telangiectasia and cutaneous dryness, severe peripheral and central hypotonia, no response to stimuli, severe muscle atrophy, and cardiomyopathy.Death occurred at 11 days of life due to the absence of spontaneous respiratory movements after discontinuing mechanical ventilation.
A muscle biopsy performed at 1 week of life revealed severe muscle atrophy and positive PAS-stained partially diastase resistant inclusions in myocytes, strongly suggestive of GSD IV.Creatine kinase were 1440 U/L at birth and decreased to 720 U/L at day 6 of life (N < 230 U/L for gestational age >39 W).GBE activity in cultured fibroblasts was <1% of the day control.Molecular studies showed a deletion of exon 7 of GBE1 gene at homozygous state in the boy, and at heterozygous state in both parents.
Two years after the birth of Patient 3, his sister (Patient 4) was born by cesarean section at 35 WG.Parents refused prenatal testing for this pregnancy which was marked by polyhydramnios and akinesia at 30 WG.The neonate girl had severe peripheral and central hypotonia, no spontaneous respiratory movements, and required intubation and mechanical ventilation.She presented abnormal movements evoking seizures, an ogival palate, adducted thumbs, and arachnodactyly without arthrogryposis.She died after 1 month due to the absence of spontaneous respiratory movements after discontinuing mechanical ventilation.GBE1 gene analysis confirmed the deletion of exon 7 at homozygous state.GBE activity was not measured.

| Patient 5
The girl was born prematurely at 30 WG from Romanian consanguineous parents.The pregnancy was marked by polyhydramnios and akinesia at 27.5 WG.At birth, she had severe hypotonia and no spontaneous respiratory movements.She was unresponsive to stimuli, and quickly presented seizures and coma.She was dysmorphic with a wide forehead and retrognathism.She had knees flexum, humeral fractures, cardiomyopathy with pulmonary arterial hypertension as well as renal and liver failure.Death occurred after 1 week due to respiratory failure.On muscle biopsy, myofibers were degenerated and reduced, but some of them contained positive PAS inclusions, diastase resistant (Figure 2I).An ultrastructural study showed widespread cytoplasmic granular-filamentous inclusions and autophagic vacuoles in muscle fibers' cytoplasm, strongly suggestive of GSD IV.The placenta was enlarged and light microscopy showed abnormal pale yellow, PAS positive, and diastase resistant inclusions in extravillous trophoblasts.These inclusions exhibited a birefringence Maltese cross pattern on polarization.At birth, creatine kinase was about 7000 U/L at day 3 of life and decreased to 360 U/L at day 7 of life (N < 552 U/L for gestational age between 28 and 32 W).GBE activity was measured at 0.3% of day control in cultured amniocytes.GBE1 gene analysis identified a variant (c.1694G>A; p.Arg565Gln) at homozygous state.Parents were not tested.

| Patient 6
A boy was the second child of non-consanguineous parents and was stillborn after a cesarean section at 30 WG due to bradycardia.Pregnancy history was marked by an increased nuchal translucency on the first trimester and hydrops fetalis with polyhydramnios at 28 WG.The autopsy showed bilateral pleural effusion, ascites, thoracic and cervical edema, moon face, hepatosplenomegaly (Figure 1A), and slight cardiac ventricular hypertrophy without cardiac malformation.Light microscopy revealed irregular inclusions, homogeneously or slightly granularly PAS positive stained, in the liver, heart, and the muscle (Figure 2J,K).The placenta was enlarged and both extravillous and villous trophoblast exhibited PAS positive-diastase resistant inclusions.GBE activity in cultured amniotic cells was found to be <1% of the day control.GBE1 gene analysis identified two variants: c.993-2A>G (p.?) inherited from the mother and c.691+2T>G (p.?) inherited from the father.Prenatal diagnosis was performed using GBE1 gene analysis on chorionic villi for the two subsequent pregnancies, and both fetuses were unaffected.The mother had one miscarriage and one extra-uterine pregnancy between the second and the third pregnancies.

| Patient 7
The female fetus was the first child of a non-consanguineous couple.Prenatal ultrasounds showed cystic hygroma and edema at 10 WG and hydrops fetalis, with ascites and akinesia at 16 WG.A termination of pregnancy (TOP) was performed at 16 WG.On post-mortem examination, the fetus presented with multiple pterygium (webbing of the skin at the joints) associated with reduced fetal movements (akinesia) resulting in muscle weakness and amyotrophy.On light microscopy abnormal PAS stained and diastase resistant inclusions of varying size were observed in muscle and heart, but not in other tissues, especially liver, central nervous system, and placenta.The karyotype performed at the first trimester on cultured chorionic villi was normal.GBE activity determination in cultured amniotic cells was 7.5% of the day control.GBE1 gene analysis identified two variants: c.955C>T (p.His319Tyr), inherited from the father and c.1580C>T (p.Thr527Met) inherited from the mother.Prenatal diagnosis was performed for the subsequent pregnancy (twin bichorial biamniotic pregnancy) by genetic testing of the GBE1 gene on chorionic villi, and both fetuses were unaffected.

| Patient 8
This was the second miscarriage of an Algerian consanguineous couple that occurred at 7.5 WG.Trophoblast histological analysis showed abnormal inclusions, strongly PAS positive, and diastase resistant, mainly located in extravillous trophoblast with Maltese cross aspect on polarization.No fetal material was available.GBE1 gene analysis showed the presence of a variant at heterozygous state for both parents: c.1064G>A (p.Arg355His).

| Patient 9
This was the second pregnancy of a nonconsanguineous couple, the first one having resulted in a voluntary abortion.There was no particular medical history except for multiple sclerosis in the mother.The female fetus had an increased nuchal translucency at the first trimester.At 22 WG, ultrasonography showed clubfeet, retrognathism, cutaneous edema, and decreased fetal movements.TOP was performed at 25 WG.On post-mortem examination, the fetus presented with arthrogryposis, multiple pterygia, facial dysmorphism (anteverted nostrils, ogival palate, hypertelorism, and retrognathism), and severe amyotrophy.There was no pulmonary hypoplasia, visceral abnormalities, or brain malformation.Histological analysis showed strongly PAS positive-diastase resistant inclusions in muscle (quadriceps).No inclusion was observed in other organs tested or placenta.GBE activity measured in muscle was <5% of the day control.GBE1 gene analysis identified two missense variants: p.His188Pro (c.563A>C) inherited from the father and p.Arg468Leu (c.1403G>T) inherited from the mother.

| Patient 10
This was the third pregnancy of an apparently nonconsanguineous couple.The first pregnancy was terminated for cystic hygroma, but no autopsy was performed.
The second pregnancy resulted in a healthy boy.Prenatal ultrasounds of the third pregnancy showed cystic hygroma, arthrogryposis, and decreased fetal movements.
TOP was performed at 16 WG.At post-mortem examination, the fetus exhibited joints contracture with multiple pterygia as well as amyotrophy with slender limbs.He also presented a Pierre Robin sequence with microretrognathism and cleft palate (Figure 1B-D).On histological examination, typical PAS positive-diastase inclusions with a Maltese cross pattern were present in placenta (trophoblast), muscle (diaphragm), and heart (Figure 2A-H).Unfortunately, GBE activity could not be performed, but molecular analyses showed a homozygous c.691+2T>C variant (p.?).GBE1 gene analysis showed the presence of the variant at heterozygous state for both parents.
The main clinical features of our cases, and those from the literature including our published cases [5][6][7] are synthetized in Figure 3.

| DISCUSSION
Severe neuromuscular forms of GSD IV are very rare and present a disastrous prognosis. Here we describe the most important case series of severe neuromuscular forms of GSD IV, mostly diagnosed after evocative histological findings, either by measurement of GBE activity (indirectly by measuring the phosphorylase activity) in muscle, fibroblasts, amniotic cells or chorionic villi, 8 and/or molecular analysis of GBE1 gene. 33A limitation of this series is that, unfortunately, for patients 1, 2 and 8, GBE deficiency was not established by enzyme/variants testing in material obtained from infants or fetuses, but rather assumed based on histological tests or results from parents.
In Figure 3, we summarized clinical and gestational findings of severe neuromuscular forms of GSD IV (formerly referred to as congenital and perinatal forms), based on our series (Table 1) and the literature analysis (Table 2) to update the review made by Escobar et al. of 29 cases of severe neuromuscular forms of GSD IV (n = 51 cases). 23evere neuromuscular forms with perinatal presentation of the disease are characterized by antenatal ultrasound abnormalities, often in the first trimester with  cystic hygroma or nuchal edema (63% of cases) associated or not with a non-immune hydrops fetalis (38%).Decreased fetal movements are often observed (50%).Lethal multiple pterygium syndrome (LMPS), FADS (characterized by multiple joint contractures, facial anomalies, and pulmonary hypoplasia), or multiple congenital arthrogryposis syndrome often occur in this form (75%). Muscle atrophy is present in 38% of perinatal cases.Intra-uterine growth restriction is observed in 25% of cases.Polyhydramnios is observed if the fetus is still alive at the late stage of pregnancy (25%).Dysmorphic features can be observed (ogival palate, retrognathism, etc.) (31%).In severe neuromuscular forms with congenital presentation, gestational warning signs can be present, but are nonspecific: polyhydramnios (69%), arthrogryposis/joint contracture (57%), and decreased fetal movements (31%).Hydrops fetalis was only observed in 6%.After birth, the main clinical sign is a major respiratory distress (89%) requiring mechanical ventilation, associated with muscle atrophy.Cardiomegaly was only present in 34%.Facial dysmorphism was found in 29% of cases (cleft palate, ogival palate, retrognathism, and wide forehead).Hepatomegaly was only present in 11% of cases.
In our series, diagnosis was suggested by histological analyses from different tissues in all tested cases.Suggestive findings are abnormal glycogen accumulation characterized by characteristic large cytoplasmic pale yellow ground-glass inclusions, PAS positive diastase resistant (Figure 2).On polarization, the inclusions harbor a birefringent Maltese cross pattern.Widespread cytoplasmic granular-filamentous inclusions seen on electronic microscopy correspond to the accumulation of abnormal glycogen.
The role of abnormal glycogen in the pathophysiology of the disease is not clearly understood.A hypothesis is that the polyglucosan bodies are considered as foreign bodies by the cells due to their reduced solubility, leading to a foreign body reaction involving cell death. 1 In a mouse model of GBE deficiency (Gbe1 À/À ), a proliferation of cardiomyocytes and ventricular insufficiency in late gestation, hydrops fetalis, and in utero death were observed. 34Abnormal glycogen accumulation in skeletal muscle and neurons is thought to be responsible for decreased fetal movements, polyhydramnios and consequently hypotonia and pulmonary hypoplasia requiring mechanical ventilation. 23n our series, when performed, placenta histological abnormalities were found in all cases but one (case 7).In the literature, placental findings were not reported in most cases (Table 2).Konstantinidou et al. 35 however described intracellular inclusions in extravillous trophoblast, similar to our cases.Other reports describe early-onset placental abnormalities, at 8, 12, and 14 WG, 7,32 suggesting that placental impairment may appear early in pregnancy.Interestingly, patient 7 who presented an isolated muscular form did not display placental impairment, as already described. 6Thus, normal placenta histological analysis does not exclude GSD IV but can be useful for diagnosis in most cases.
Miscarriage is another possible presentation of severe neuromuscular forms of GSD IV.In our series, miscarriage history was found in three families.Among them, only one placenta histological analysis could be performed, showing extravillous trophoblast inclusions.Thus, histological analysis of the placenta in the case of repeated miscarriages could suggest GSD IV.Inclusions can be observed in the placenta since 7.5 WG as in patient 8, leading to perform GBE1 gene analysis in the fetus or in both parents, to confirm the diagnosis allowing genetic counseling and prenatal testing for further pregnancies.
As mentioned above, biochemical diagnosis relies on GBE activity measurement performed on the available tissue in addition to GBE1 gene analysis.As advocated by Koch and colleagues, GBE activity should always be conducted in case of inconclusive molecular testing despite strong clinical suspicion. 4Correlation between residual GBE activity and clinical severity cannot be made due to a variability depending on cell type, and due to the method used (which is an indirect assay dependent on phosphorylase as the indicating enzyme). 8However, the absence of GBE activity may be critical in some tissues during fetal life.The accumulation of amylopectin-like glycogen in skeletal muscle is responsible for hypotonia leading to decreased fetal movements, and the occurrence of hydrops in some cases.Also, functional abnormalities of the fetal heart should contribute to hydrops fetalis. 34In contrast, isolated hepatic form has not been described with onset at birth or in utero.
The GBE1 gene is located on chromosome 3 (3p12.2). 33 It comprises 16 exons for an approximate size of 272 kb and encodes a 702 amino acids protein.More than 120 pathogenic or likely pathogenic variants have been reported, including missense, nonsense, small insertions or deletions leading to frameshift, large deletions of one or more exons, and splice-site variants. 4,36Genotype-phenotype correlation are difficult to establish.Still, null pathogenic variants are associated with a more severe phenotype, 15,24 while missense pathogenic variants display a more variable impact on clinical severity.Most missense variants are located in the catalytic domain of GBE encompassing amino acid residues 184-600.
In our series, GBE1 gene variants were identified in all cases (Table 1), either on DNA extracted from fetal material when available, or on DNA from both parents (patients 1, 2, and 8).In the families where consanguinity was confirmed (4 out of 8 families), parents of the affected children were always first cousins.We found a deletion of exon 7 in 2 siblings (cases 3 and 4), and 11 different variants have been identified.Among them, we identified five variants not previously reported in the literature (3 missense: p.Arg468Leu, p.Thr527Met, p.-Trp548Leu and 2 splice-site: c.691+2T>G, c.993-2A>G) (Table 1).Genotypes with null variants at the homozygous state (patients 3, 4, and 10) or compound heterozygous state (patient 6) are well correlated with a severe phenotype.A missense variant is present at the homozygous state in four patients (patients 1, 2, 5, and 8) and two patients are compound heterozygotes (patients 7 and 9).The three novel missense variants are predicted as probably pathogenic as: (i) they affect an amino acid highly conserved between species, (ii) they are absent or referenced at a very low frequency in gnomAD database (Genome Aggregation Database, https://gnomad.broadinstitute.org/),and (iii) in silico bioinformatic prediction tools (SIFT, Mutation Taster, PolyPhen-2) suggest that these variants may impact the protein function.Further functional studies are however required to confirm their pathogenicity.GBE1 variants previously described in severe neuromuscular forms of GSD IV are listed in Table 2.The majority are severe variants (null allele): splicing variants, small deletions and/or insertions, large deletions, nonsense variants.Only eight variants are missense variants whose impact on protein function is more difficult to determine.In total, out of the 27 genotyped patients, 20 patients have a clearly severe genotype (including 14 homozygotes), consistent with a severe phenotype.In the case described by Burrow et al., the presence of two GBE1 missense variants (p.Gln236His and p.Arg262Cys) could explain a milder phenotype. 16egarding the genotype-phenotype correlations, intrafamilial clinical presentation can be either similar in siblings (patients 1 and 2) or different (patients 3 and 4), and this finding is in good agreement with the literature.On the one hand, Cox et al. described cases of perinatal GSD IV with the same phenotype during three successive pregnancies 29 in an identical time of onset, and Ravenscroft et al. described the case of siblings with the same phenotype of fetal akinesia with LMPS whose diagnosis of GSD IV was made by exome sequencing: the fetuses were heterozygous for a variant affecting a consensus splice site (c.691+2T>C) and a novel missense variant (c.956A>C p.His319Arg). 30On the other hand, for the same genotype, a different phenotype was observed in our series (patients 3 and 4): only the first child with a congenital form presented with arthrogryposis and dysmorphia.Intrafamilial variability was also reported by L'Herminé-Coulomb et al.: a prenatal cervical cystic hygroma was present in both cases but associated with hydrops fetalis in one, and fetal akinesia without hydrops fetalis in the other. 6ntenatal diagnosis is feasible on cultured chorionic villi cells sampled at 10 WG or on cultured amniotic cells after amniocentesis at 14 WG.Diagnosis is preferably made by molecular studies if the genotype was identified in the affected familial case, but GBE activity can be performed as well, especially in case without specific ultrasound signs (e.g., decreased fetal movements, cystic hygroma, hydrops fetalis, and arthrogryposis) or in cases with variant of uncertain significance in the GBE1 gene.To date, there is no specific treatment for GSD IV, and the prognosis for these severe neuromuscular forms is very poor, leading to death at birth or within the first months of life.Gene therapy could be a therapeutic lead, 37 as well as abnormal glycogen accumulation prevention.Polyglucosan formation and accumulation in CNS appears to be restrained by glycogen synthase inhibition. 38

| CONCLUSION
Severe neuromuscular forms are rare presentations of GSD IV with a very poor prognosis.In our series of 10 cases, we found similar clinical features than the previous reports in the literature and identified 5 novel GBE1 variants.As histological findings were always highly suggestive of the disease, we emphasize the importance of performing a pathological examination of both the fetus and placenta in all cases, including unexplained early miscarriages cases.Antenatal features such as cystic hygroma, hydrops fetalis, arthrogryposis/joint contractures for perinatal forms, or decreased fetal movements and polyhydramnios, as well as severe hypotonia at birth with muscle atrophy and arthrogryposis, should prompt the research for GSD IV.This gene is also included in various diagnostic gene panels such as congenital myopathy, arthrogryposis, and fetal akinesia.The development of the prenatal exome should facilitate this diagnosis.
Even though this disease is very rare, it is probably underdiagnosed.No current specific treatment is available to date and a better understanding of the disease is required in order to identify therapeutic leads.

F
I G U R E 3 Clinical features of perinatal and congenital forms of GSD IV. (A) Antenatal signs.(B) Postnatal signs.FADS, fetal akinesia deformation sequence; LMPS, lethal multiple pterygium syndrome.Neuromuscular findings: hypotonia, muscular dystrophy, or amyotrophy.Dysmorphic features: retrognathism, cleft or ogival palate, wide forehead.Respiratory findings: need for mechanical ventilation, pulmonary hypoplasia.T A B L E 2 Severe neuromuscular cases of GSD IV (formerly distinguished as congenital and perinatal) published until December 2022.
This table has been compiled by the authors from an exhaustive but not systematic review of the literature.Abbreviations: a, b, c, d, e, f: respectively related; CNS, central nervous system; DFM, decreased fetal movements; F, female; FADS, fetal akinesia deformation sequence; IUGR, intrauterine growth restriction; LMPS, lethal multiple pterygium syndrome; M, male; MA, medical abortion; MCMATP, monochorionic monoamniotic twin pregnancy; ND, not determined; WG, week of gestation.