Phenotypic spectrum and genomics of undiagnosed arthrogryposis multiplex congenita.

BACKGROUND: Arthrogryposis multiplex congenita (AMC) is characterised by congenital joint contractures in two or more body areas. AMC exhibits wide phenotypic and genetic heterogeneity. Our goals were to improve the genetic diagnosis rates of AMC, to evaluate the added value of whole exome sequencing (WES) compared with targeted exome sequencing (TES) and to identify new genes in 315 unrelated undiagnosed AMC families. METHODS: Several genomic approaches were used including genetic mapping of disease loci in multiplex or consanguineous families, TES then WES. Sanger sequencing was performed to identify or validate variants. RESULTS: We achieved disease gene identification in 52.7% of AMC index patients including nine recently identified genes (CNTNAP1, MAGEL2, ADGRG6, ADCY6, GLDN, LGI4, LMOD3, UNC50 and SCN1A). Moreover, we identified pathogenic variants in ASXL3 and STAC3 expanding the phenotypes associated with these genes. The most frequent cause of AMC was a primary involvement of skeletal muscle (40%) followed by brain (22%). The most frequent mode of inheritance is autosomal recessive (66.3% of patients). In sporadic patients born to non-consanguineous parents (n=60), de novo dominant autosomal or X linked variants were observed in 30 of them (50%). CONCLUSION: New genes recently identified in AMC represent 21% of causing genes in our cohort. A high proportion of de novo variants were observed indicating that this mechanism plays a prominent part in this developmental disease. Our data showed the added value of WES when compared with TES due to the larger clinical spectrum of some disease genes than initially described and the identification of novel genes.

Loss-of-Function Mutations in LGI4, a Secreted Ligand Involved in Schwann Cell Myelination, Are Responsible for Arthrogryposis Multiplex Congenita.

Arthrogryposis multiplex congenita (AMC) is a developmental condition characterized by multiple joint contractures resulting from reduced or absent fetal movements. Through genetic mapping of disease loci and whole-exome sequencing in four unrelated multiplex families presenting with severe AMC, we identified biallelic loss-of-function mutations in LGI4 (leucine-rich glioma-inactivated 4). LGI4 is a ligand secreted by Schwann cells that regulates peripheral nerve myelination via its cognate receptor ADAM22 expressed by neurons. Immunolabeling experiments and transmission electron microscopy of the sciatic nerve from one of the affected individuals revealed a lack of myelin. Functional tests using affected individual-derived iPSCs showed that these germline mutations caused aberrant splicing of the endogenous LGI4 transcript and in a cell-based assay impaired the secretion of truncated LGI4 protein. This is consistent with previous studies reporting arthrogryposis in Lgi4-deficient mice due to peripheral hypomyelination. This study adds to the recent reports implicating defective axoglial function as a key cause of AMC.

Understanding high rates of stillbirth and neonatal death in a disadvantaged, high-migrant district in France: A perinatal audit.

INTRODUCTION: The objective of this study is to investigate factors associated with risks of perinatal death in a disadvantaged, high-migrant French district with mortality rates above the national average. MATERIAL AND METHODS: The study design is a perinatal audit in 2014 in all 11 maternity units in the Seine-Saint-Denis district (25 037 births). The data come from medical chart abstraction, maternal interviews and peer assessor confidential review of deaths. A representative sample of live births in the same district, from the 2010 French Perinatal Survey, was used for comparisons (n = 429). The main outcome measures were stillbirth and neonatal death (0-27 days) at ≥22 weeks of gestation. RESULTS: The audit included 218 women and 227 deaths (156 stillbirths, 71 neonatal deaths); 75 women were interviewed. In addition to primiparity and multiple pregnancy, overweight and obesity increased mortality risks (50% of cases, adjusted odds ratios [aOR] 1.7, 95% confidence interval [CI] 1.1-2.8, and aOR 1.9 [95% CI 1.1-3.2], respectively) as did the presence of preexisting medical/obstetric conditions (28.6% of cases, aOR 3.2, 95% CI 2.0-5.3). Problems accessing or complying with care were noted in 25% of medical records and recounted in 50% of interviews. Assessors identified suboptimal factors in 73.2% of deaths and judged 33.9% to be possibly or probably preventable. Care not adapted to risk factors and poor healthcare coordination were frequent suboptimal factors. Possibly preventable deaths were higher (P < .05) for women with gestational diabetes or hypertension (44.6%) than women without (29.0%). CONCLUSIONS: Preventive actions to improve healthcare referral and coordination, especially for overweight and obese women and women with medical and obstetrical risk factors, could reduce perinatal mortality in disadvantaged areas.

Fraser syndrome: features suggestive of prenatal diagnosis in a review of 38 cases.

OBJECTIVE: Fraser syndrome (FS) is a rare malformation recessive disorder. Major criteria are cryptophtalmos, syndactyly, respiratory, genital and urinary tract anomalies. Few prenatal presentations have been reported. METHOD: We analyzed the prenatal and postnatal fetal phenotype in 38 cases of FS, including 25 pregnancy termination cases, 8 intra-uterine death cases and 4 cases that died after birth. RESULTS: Including both prenatal and postnatal fetal phenotypic evaluation, all cases presented dysmorphic features with nose and ear dysplasia. Renal anomalies and syndactyly were present in 37/38 cases, cryptophtalmos in 36/38, airways anomalies in 30/37 and genital anomalies in 30/35 cases. Anomalies of the abdominal wall such as low set umbilicus and omphalocele were found in 31 cases. Among the 26 cases for which ultrasound data were available, detectable anomalies included oligohydramnios (22), ascites/hydrops (9), renal anomalies (20), evidence for high airways obstruction (11), ophthalmologic anomalies (4), ear dysplasia (2) and syndactyly (2). CONCLUSION: This study shows that the postnatal phenotype of FS is very specific, whereas oligohydramnios hampers the prenatal recognition of the cardinal FS diagnosis criteria. Association of oligohydramnios, kidney agenesis and CHAOS should lead to consider this diagnosis. © 2016 John Wiley & Sons, Ltd.

Radiographic features of the skeleton in disorders of post-squalene cholesterol biosynthesis.

Disorders of post-squalene cholesterol biosynthesis are inborn errors of metabolism characterised by multiple congenital abnormalities, including significant skeletal involvement. The most frequent and best-characterised example is the Smith-Lemli-Opitz syndrome. Nine other disorders are known, namely autosomal-recessive Antley-Bixler syndrome, Greenberg dysplasia, X-linked dominant chondrodysplasia punctata, X-linked recessive male emopamil-binding protein deficiency, CHILD syndrome, CK syndrome, sterol C4 methyloxidase-like deficiency, desmosterolosis and lathosterolosis. This study provides an overview of the radiologic features observed in these diseases. A common pattern of limb abnormalities is recognisable, including polydactyly, which is typically post-axial and rarely interdigital and can involve all four limbs, and syndactyly of the toes. Chondrodysplasia punctata is specifically associated with a subgroup of disorders of cholesterol biosynthesis (Greenberg dysplasia, CHILD syndrome, X-linked dominant chondrodysplasia punctata, male emopamil-binding protein deficiency). The possible occurrence of epiphyseal stippling in the Smith-Lemli-Opitz syndrome, initially reported, does not appear to be confirmed. Stippling is also associated with other congenital disorders such as chromosomal abnormalities, brachytelephalangic chondrodysplasia punctata (X-linked recessive chondrodysplasia punctata, disruptions of vitamin K metabolism, maternal autoimmune diseases), rhizomelic chondrodysplasia punctata (peroxisomal disorders) and lysosomal storage disorders. In the differential diagnosis of epiphyseal stippling, a moth-eaten appearance of bones, asymmetry, or presence of a common pattern of limb abnormalities indicate inborn errors of cholesterol biosynthesis. We highlight the specific differentiating radiologic features of disorders of post-squalene cholesterol biosynthesis.

Antiphospholipid syndrome and other autoimmune diseases associated with chronic intervillositis.

OBJECTIVES: Chronic intervillositis of unknown etiology (CIUE) is characterized by an intervillous infiltrate of mononuclear cells and a high recurrence rate of adverse obstetrical outcomes. The aim was to describe obstetrical history in patients with at least one event characterized by CIUE, and the possible impact of systematic investigation of an underlying autoimmune disease on the obstetrical outcome of subsequent pregnancies. METHODS: We retrospectively reviewed all pregnancies in patients having experienced at least one adverse obstetric outcome associated with chronic intervillositis of unknown etiology diagnosed by placental histological analysis between 2004 and 2011 in our university hospital. For each patient, data pertaining to obstetrical history, treatments during pregnancies, the results of systematic investigation of an underlying autoimmune disease, and treatments as well as obstetrical outcome in subsequent pregnancies, were collected. RESULTS: Twelve patients with 38 pregnancies were included [median age 30 (22; 40 years)]. Autoimmune disease or autoimmune antibodies (AID group) were found in 7/12 patients: primary antiphospholipid syndrome (APS) (n = 4), Sjögren's syndrome (n = 1), pernicious anemia (n = 1) and celiac disease (n = 1). When comparing pregnancies of patients with and without AID, there was no difference with regard to the type of obstetrical events or live-born babies, in spite of appropriate treatment. Corticosteroids (prednisone 10 mg/day) were used in only 2 cases with AID (Sjögren's syndrome and APS; n = 1 each), and these 2 pregnancies resulted in live-born babies. CONCLUSION: This study shows that the immunological assessment in patients with CIUE raises the possibility of a specific severity when AID or obstetrical APS is associated with CIUE, since conventional treatment did not improve obstetrical outcome in these patients as compared to those without autoimmune diseases. The benefit of immunosuppressant agents in this subset of patients needs further evaluation.

The transmembrane protein meckelin (MKS3) is mutated in Meckel-Gruber syndrome and the wpk rat.

Meckel-Gruber syndrome is a severe autosomal, recessively inherited disorder characterized by bilateral renal cystic dysplasia, developmental defects of the central nervous system (most commonly occipital encephalocele), hepatic ductal dysplasia and cysts and polydactyly. MKS is genetically heterogeneous, with three loci mapped: MKS1, 17q21-24 (ref. 4); MKS2, 11q13 (ref. 5) and MKS3 (ref. 6). We have refined MKS3 mapping to a 12.67-Mb interval (8q21.13-q22.1) that is syntenic to the Wpk locus in rat, which is a model with polycystic kidney disease, agenesis of the corpus callosum and hydrocephalus. Positional cloning of the Wpk gene suggested a MKS3 candidate gene, TMEM67, for which we identified pathogenic mutations for five MKS3-linked consanguineous families. MKS3 is a previously uncharacterized, evolutionarily conserved gene that is expressed at moderate levels in fetal brain, liver and kidney but has widespread, low levels of expression. It encodes a 995-amino acid seven-transmembrane receptor protein of unknown function that we have called meckelin.

Prenatal assessment of a fast-growing giant epignathus.

Epignathus is a very rare fetal tumor. We report a case of fast-growing giant epignathus with severe distortion of the right part of the face and orbit. A thorough prenatal work-up was performed by the association of Magnetic Resonance Imaging and Ultrasonography. A multidisciplinary approach was crucial to assess the operability and provide careful counseling to help parents understand and reach decision.

Neuropathological review of 138 cases genetically tested for X-linked hydrocephalus: evidence for closely related clinical entities of unknown molecular bases.

L1 syndrome results from mutations in the L1CAM gene located at Xq28. It encompasses a wide spectrum of diseases, X-linked hydrocephalus being the most severe phenotype detected in utero, and whose pathophysiology is incompletely understood. The aim of this study was to report detailed neuropathological data from patients with mutations, to delineate the neuropathological criteria required for L1CAM gene screening in foetuses by characterizing the sensitivity, specificity and positive predictive value of the cardinal signs, and to discuss the main differential diagnoses in non-mutated foetuses in order to delineate closely related conditions without L1CAM mutations. Neuropathological data from 138 cases referred to our genetic laboratory for screening of the L1CAM gene were retrospectively reviewed. Fifty-seven cases had deleterious L1CAM mutations. Of these, 100 % had hydrocephalus, 88 % adducted thumbs, 98 % pyramidal tract agenesis/hypoplasia, 90 % stenosis of the aqueduct of Sylvius and 68 % agenesis/hypoplasia of the corpus callosum. Two foetuses had L1CAM mutations of unknown significance. Seventy-nine cases had no L1CAM mutations; these were subdivided into four groups: (1) hydrocephalus sometimes associated with corpus callosum agenesis (44 %); (2) atresia/forking of the aqueduct of Sylvius/rhombencephalosynapsis spectrum (27 %); (3) syndromic hydrocephalus (9 %), and (4) phenocopies with no mutations in the L1CAM gene (20 %) and in whom family history strongly suggested an autosomal recessive mode of transmission. These data underline the existence of closely related clinical entities whose molecular bases are currently unknown. The identification of the causative genes would greatly improve our knowledge of the defective pathways involved in these cerebral malformations.

Cobblestone lissencephaly: neuropathological subtypes and correlations with genes of dystroglycanopathies.

Cobblestone lissencephaly represents a peculiar brain malformation with characteristic radiological anomalies, defined as cortical dysplasia combined with dysmyelination, dysplastic cerebellum with cysts and brainstem hypoplasia. Cortical dysplasia results from neuroglial overmigration into the arachnoid space, forming an extracortical layer, responsible for agyria and/or 'cobblestone' brain surface and ventricular enlargement. The underlying mechanism is a disruption of the glia limitans, the outermost layer of the brain. Cobblestone lissencephaly is pathognomonic of a continuum of autosomal recessive diseases with cerebral, ocular and muscular deficits, Walker-Warburg syndrome, muscle-eye-brain and Fukuyama muscular dystrophy. Mutations in POMT1, POMT2, POMGNT1, LARGE, FKTN and FKRP genes attributed these diseases to α-dystroglycanopathies. However, studies have not been able to identify causal mutations in the majority of patients and to establish a clear phenotype/genotype correlation. Therefore, we decided to perform a detailed neuropathological survey and molecular screenings in 65 foetal cases selected on the basis of histopathological criteria. After sequencing the six genes of α-dystroglycanopathies, a causal mutation was observed in 66% of cases. On the basis of a ratio of severity, three subtypes clearly emerged. The most severe, which we called cobblestone lissencephaly A, was linked to mutations in POMT1 (34%), POMT2 (8%) and FKRP (1.5%). The least severe, cobblestone lissencephaly C, was linked to POMGNT1 mutations (18%). An intermediary type, cobblestone lissencephaly B, was linked to LARGE mutations (4.5%) identified for the first time in foetuses. We conclude that cobblestone lissencephaly encompasses three distinct subtypes of cortical malformations with different degrees of neuroglial ectopia into the arachnoid space and cortical plate disorganization regardless of gestational age. In the cerebellum, histopathological changes support the novel hypothesis that abnormal lamination arises from a deficiency in granule cells. Our studies demonstrate the positive impact of histoneuropathology on the identification of α-dystroglycanopathies found in 66% of cases, while with neuroimaging criteria and biological values, mutations are found in 32-50% of patients. Interestingly, our morphological classification was central in the orientation of genetic screening of POMT1, POMT2, POMGNT1, LARGE and FKRP. Despite intensive research, one-third of our cases remained unexplained; suggesting that other genes and/or pathways may be involved. This material offers a rich resource for studies on the affected neurodevelopmental processes of cobblestone lissencephaly and on the identification of other responsible gene(s)/pathway(s).

Antenatal spectrum of CHARGE syndrome in 40 fetuses with CHD7 mutations.

BACKGROUND: CHARGE syndrome is a rare, usually sporadic disorder of multiple congenital anomalies ascribed to a CHD7 gene mutation in 60% of cases. Although the syndrome is well characterised in children, only one series of 10 fetuses with CHARGE syndrome has been reported to date. Therefore, we performed a detailed clinicopathological survey in our series of fetuses with CHD7 mutations, now extended to 40 cases. CHARGE syndrome is increasingly diagnosed antenatally, but remains challenging in many instances. METHOD: Here we report a retrospective study of 40 cases of CHARGE syndrome with a CHD7 mutation, including 10 previously reported fetuses, in which fetal or neonatal clinical, radiological and histopathological examinations were performed. RESULTS: Conversely to postnatal studies, the proportion of males is high in our series (male to female ratio 2.6:1) suggesting a greater severity in males. Features almost constant in fetuses were external ear anomalies, arhinencephaly and semicircular canal agenesis, while intrauterine growth retardation was never observed. Finally, except for one, all other mutations identified in our antenatal series were truncating, suggesting a possible phenotype-genotype correlation. CONCLUSIONS: Clinical analysis allowed us to refine the clinical description of CHARGE syndrome in fetuses, describe some novel features and set up diagnostic criteria in order to help the diagnosis of CHARGE syndrome after termination of pregnancies following the detection of severe malformations.

Pontocerebellar hypoplasia with rhombencephalosynapsis and microlissencephaly expands the spectrum of PCH type 1B.

Rhombencephalosynapsis is a rare cerebellar malformation developing during embryogenesis defined by vermian agenesis or hypogenesis with fusion of the cerebellar hemispheres. It occurs either alone or in association with other cerebral and/or extracerebral anomalies. Its association with microlissencephaly is exceedingly rare and to date, only a heterozygous de novo missense variant in ADGRL2, a gene encoding Adhesion G-Protein-Coupled Receptor L2, has been identified. We report on two siblings of Roma origin presenting with severe growth retardation, fetal akinesia, microlissencephaly and small cerebellum with vermian agenesis. Neuropathological studies revealed extreme paucity in pontine transverse fibres, rudimentary olivary nuclei and rhombencephalosynapsis with vanishing spinal motoneurons in both fetuses. Comparative fetus-parent exome sequencing revealed in both fetuses a homozygous variant in exon 1 of the EXOSC3 gene encoding a core component of the RNA exosome, c.92G > C; p.(Gly31Ala). EXOSC3 accounts for 40%-75% of patients affected by ponto-cerebellar hypoplasia with spinal muscular atrophy (PCH1B). The c.92G > C variant is a founder mutation in the Roma population and has been reported in severe PCH1B. PCH1B is characterized by a broad phenotypic spectrum, ranging from mild phenotypes with spasticity, mild to moderate intellectual disability, pronounced distal muscular and cerebellar atrophy/hypoplasia, to severe phenotypes with profound global developmental delay, progressive microcephaly and atrophy of the cerebellar hemispheres. In PCH1B, the usual cerebellar lesions affect mainly the hemispheres with relative sparing of vermis that radically differs from rhombencephalosynapsis. This unusual foetal presentation expands the spectrum of PCH1B and highlights the diversity of rhombencephalosynapsis etiologies.

Phenotypic and Neuropathological Characterization of Fetal Pyruvate Dehydrogenase Deficiency.

To distinguish pyruvate dehydrogenase deficiency (PDH) from other antenatal neurometabolic disorders thereby improving prenatal diagnosis, we describe imaging findings, clinical phenotype, and brain lesions in fetuses from 3 families with molecular characterization of this condition. Neuropathological analysis was performed in 4 autopsy cases from 3 unrelated families with subsequent biochemical and molecular confirmation of PDH complex deficiency. In 2 families there were mutations in the PDHA1 gene; in the third family there was a mutation in the PDHB gene. All fetuses displayed characteristic craniofacial dysmorphism of varying severity, absence of visceral lesions, and associated encephaloclastic and developmental supra- and infratentorial lesions. Neurodevelopmental abnormalities included microcephaly, migration abnormalities (pachygyria, polymicrogyria, periventricular nodular heterotopias), and cerebellar and brainstem hypoplasia with hypoplastic dentate nuclei and pyramidal tracts. Associated clastic lesions included asymmetric leukomalacia, reactive gliosis, large pseudocysts of germinolysis, and basal ganglia calcifications. The diagnosis of PDH deficiency should be suspected antenatally with the presence of clastic and neurodevelopmental lesions and a relatively characteristic craniofacial dysmorphism. Postmortem examination is essential for excluding other closely related entities, thereby allowing for biochemical and molecular confirmation.

[Audit of obstetrical practices and prevention of perinatal deaths]. / Audit des pratiques obstétricales: influence sur la mortalité périnatale.

An audit of obstetrical practices, defined here as a critical analysis of practices, was accepted by the local authorities and obstetricians/pediatricians of the district of Seine-Saint-Denis (northern Paris, France). The study analyzed all perinatal deaths occurring during a three-year period (the Perinatal Enquiry, 1 Oct. 1989 to 30 Sept. 1992) and subsequently became a permanent tool for critical analysis of obstetrical practices. Bimonthly meetings of obstetricians and pediatricians were held to discuss observed fetal and neonatal deaths. This intervention was associated with a major reduction in perinatal mortality rates after a 10-year period.

Prenatal Diagnosis of Antley-Bixler Syndrome and POR Deficiency.

BACKGROUND: Prenatal diagnosis of severe bone diseases is challenging and requires complete and precise analysis of fetal anomalies to guide genetic investigation and parental counselling. CASE REPORT: We report a rare case of Antley-Bixler syndrome prenatally diagnosed at 26 weeks' gestation by ultrasound and computed tomography in a 28-year-old woman with a history of early termination of pregnancy for "malposition of the inferior limbs". The prenatal ultrasound scan showed severe femoral bowing and frontal bossing. Taking into account the high probability of a recurrent severe skeletal disorder, a computed tomography (CT) scan was proposed. CT findings revealed bilateral femora deformation, craniosynostosis, severe midface hypoplasia, and radiohumeral synostosis. These anomalies strongly suggested Antley-Bixler syndrome. Sequencing of the POR gene in the fetus and the parents revealed compound heterozygous mutations in exon 9 and intron 7, both inherited from each parent, and this finding allowed genetic counseling. CONCLUSIONS: The first step in the proper prenatal diagnosis of fetal bone disorders is the precise analysis of ultrasonographic images. However, when a severe fetal inherited disorder is strongly suspected in late mid-trimester, CT may be discussed and usefully contribute to diagnosis and prognosis assessment.

Chronic histiocytic intervillositis: outcome, associated diseases and treatment in a multicenter prospective study.

UNLABELLED: Introduction: In this prospective multicenter study, we aimed to describe (1) the outcome of pregnancy in the case of previous chronic histiocytic intervillositis (CHI), (2) the immunological findings and associated diseases, (3) the treatments, and (4) the factors associated with pregnancy loss. METHODS: We prospectively included all patients with a prior CHI with ongoing pregnancy between 2011 and 2013. RESULTS: Twenty-four women (age 34±5 years) were included in this study. An autoimmune disease was present in seven (29%) cases. Twenty-one prospective pregnancies were treated. The number of live births was more frequent comparatively to the previous obstetrical issues (16/24 versus 24/76; p=0.003). Most of the pregnancies were treated (88%), whereas only 13% of previous pregnancies were treated (p<0.05). No difference was found with respect to the pregnancy outcome in the different treatment regimens. In univariate analyses, a prior history of intrauterine death and intrauterine growth restriction and the presence of CHI in prospective placentas were associated with failure to have a live birth. DISCUSSION: In this multicenter study, we show the frequency of the associated autoimmune diseases in CHI, as well as the presence of autoantibodies without characterized autoimmune disease. The number of live births increased from 32% to 67% in the treated pregnancies. Despite the treatment intervention, the risk of preterm delivery remained at 30%. Last, we show that the recurrence rate of an adverse pregnancy outcome persisted at 30% despite treatment intervention. CONCLUSION: CHI is associated with high recurrence rate and the combined regimen seems to be necessary, in particular, in the presence of previous intrauterine death.

3D-FISH analysis reveals chromatid cohesion defect during interphase in Roberts syndrome.

BACKGROUND: Roberts syndrome (RBS) is a rare autosomal recessive disorder mainly characterized by growth retardation, limb defects and craniofacial anomalies. Characteristic cytogenetic findings are "railroad track" appearance of chromatids and premature centromere separation in metaphase spreads. Mutations in the ESCO2 (establishment of cohesion 1 homolog 2) gene located in 8p21.1 have been found in several families. ESCO2, a member of the cohesion establishing complex, has a role in the effective cohesion between sister chromatids. In order to analyze sister chromatids topography during interphase, we performed 3D-FISH using pericentromeric heterochromatin probes of chromosomes 1, 4, 9 and 16, on preserved nuclei from a fetus with RBS carrying compound heterozygous null mutations in the ESCO2 gene. RESULTS: Along with the first observation of an abnormal separation between sister chromatids in heterochromatic regions, we observed a statistically significant change in the intranuclear localization of pericentromeric heterochromatin of chromosome 1 in cells of the fetus compared to normal cells, demonstrating for the first time a modification in the spatial arrangement of chromosome domains during interphase. CONCLUSION: We hypothesize that the disorganization of nuclear architecture may result in multiple gene deregulations, either through disruption of DNA cis interaction -such as modification of chromatin loop formation and gene insulation - mediated by cohesin complex, or by relocation of chromosome territories. These changes may modify interactions between the chromatin and the proteins associated with the inner nuclear membrane or the pore complexes. This model offers a link between the molecular defect in cohesion and the complex phenotypic anomalies observed in RBS.