Multiple Pterygium Syndrome Research Articles

Periderm prevents pathological epithelial adhesions during embryogenesis.

Appropriate development of stratified, squamous, keratinizing epithelia, such as the epidermis and oral epithelia, generates an outer protective permeability barrier that prevents water loss, entry of toxins, and microbial invasion. During embryogenesis, the immature ectoderm initially consists of a single layer of undifferentiated, cuboidal epithelial cells that stratifies to produce an outer layer of flattened periderm cells of unknown function. Here, we determined that periderm cells form in a distinct pattern early in embryogenesis, exhibit highly polarized expression of adhesion complexes, and are shed from the outer surface of the embryo late in development. Mice carrying loss-of-function mutations in the genes encoding IFN regulatory factor 6 (IRF6), IκB kinase-α (IKKα), and stratifin (SFN) exhibit abnormal epidermal development, and we determined that mutant animals exhibit dysfunctional periderm formation, resulting in abnormal intracellular adhesions. Furthermore, tissue from a fetus with cocoon syndrome, a lethal disorder that results from a nonsense mutation in IKKA, revealed an absence of periderm. Together, these data indicate that periderm plays a transient but fundamental role during embryogenesis by acting as a protective barrier that prevents pathological adhesion between immature, adhesion-competent epithelia. Furthermore, this study suggests that failure of periderm formation underlies a series of devastating birth defects, including popliteal pterygium syndrome, cocoon syndrome, and Bartsocas-Papas syndrome.

Mutation Update and Genotype-Phenotype Correlations of Novel and Previously Described Mutations inTPM2andTPM3Causing Congenital Myopathies

Mutations affecting skeletal muscle isoforms of the tropomyosin genes may cause nemaline myopathy, cap myopathy, core-rod myopathy, congenital fiber-type disproportion, distal arthrogryposes, and Escobar syndrome. We correlate the clinical picture of these diseases with novel (19) and previously reported (31) mutations of the TPM2 and TPM3 genes. Included are altogether 93 families: 53 with TPM2 mutations and 40 with TPM3 mutations. Thirty distinct pathogenic variants of TPM2 and 20 of TPM3 have been published or listed in the Leiden Open Variant Database (http://www.dmd.nl/). Most are heterozygous changes associated with autosomal-dominant disease. Patients with TPM2 mutations tended to present with milder symptoms than those with TPM3 mutations, DA being present only in the TPM2 group. Previous studies have shown that five of the mutations in TPM2 and one in TPM3 cause increased Ca(2+) sensitivity resulting in a hypercontractile molecular phenotype. Patients with hypercontractile phenotype more often had contractures of the limb joints (18/19) and jaw (6/19) than those with nonhypercontractile ones (2/22 and 1/22), whereas patients with the non-hypercontractile molecular phenotype more often (19/22) had axial contractures than the hypercontractile group (7/19). Our in silico predictions show that most mutations affect tropomyosin-actin association or tropomyosin head-to-tail binding.

Prenatal Sonographic Detection of Skeletal Dysplasias

Skeletal dysplasias are a genetically heterogeneous group of disorders that can be diagnosed prenatally by sonography. Differentiating these disorders in the prenatal period can be difficult. However, differentiating known lethal disorders from nonlethal disorders can improve patient care and plan of action. This case study presents multiple pterygia, flexion contractures, and skeletal abnormalities, which are consistent with multiple pterygium syndrome, or Escobar syndrome.

Nicotinic acetylcholine receptors in human genetic disease

Nicotinic acetylcholine receptors represent a family of ligand-gated ion channels that are widely expressed in the central and peripheral nervous systems. To date, 16 genes encoding subunits of mammalian nicotinic acetylcholine receptors have been identified. The various subunits form homomeric or heteromeric receptor proteins, allowing for a complex and adaptable system of nicotinic neurotransmission. Mutations of nicotinic receptor genes can cause Mendelian disorders, most importantly congenital myasthenic syndromes, multiple pterygium syndromes, and nocturnal frontal lobe epilepsies. Haploinsufficiency of CHRNA7 predisposes to neuropsychiatric phenotypes in 15q13.3 deletion syndrome. The role of various nicotinic receptor genes is also discussed for complex disorders such as addiction, schizophrenia, Alzheimer disease, and Parkinson disease.

Nonlethal Multiple Pterygium Syndrome

Nonlethal Escobar is a rare disorder that is a variant of multiple pterygium syndromes. It is a form of arthrogryposis multiplex congenita characterized by excessive webbing (pterygia), congenital contractures (arthrogryposis), and scoliosis. It is usually diagnosed in utero on fetal ultrasound and then confirmed in the neonatal period. A case of nonlethal neonatal Escobar is reported in a 35-week-and-6-day old infant who presented in utero with decreased fetal movement, oligohydramnios, and arthrogryposis. The etiologies from maternal causes were excluded prior to birth. Subsequent workup after birth led to a highly suspected diagnosis of nonlethal Escobar by the geneticist. The diagnosis was confirmed by a positive CHRNG gene sequence analysis after discharge. The infant demonstrated contractures and bilateral hip subluxation but was feeding well and was discharged home with outpatient follow-up. Treatment after discharge has been extensive secondary to difficulties associated with this disease. The clinical presentation of nonlethal Escobar, as well as diagnosis and treatment strategies, is provided with caregiving strategies.

Germline mutations in RYR1 are associated with foetal akinesia deformation sequence/lethal multiple pterygium syndrome

Foetal akinesia deformation sequence syndrome (FADS) is a genetically heterogeneous disorder characterised by the combination of foetal akinesia and developmental defects which may include pterygia (joint webbing). Traditionally multiple pterygium syndrome (MPS) has been divided into two forms: prenatally lethal (LMPS) and non-lethal Escobar type (EVMPS) types. Interestingly, FADS, LMPS and EVMPS may be allelic e.g. each of these phenotypes may result from mutations in the foetal acetylcholine receptor gamma subunit gene (CHRNG). Many cases of FADS and MPS do not have a mutation in a known FADS/MPS gene and we undertook molecular genetic studies to identify novel causes of these phenotypes. After mapping a novel locus for FADS/LMPS to chromosome 19, we identified a homozygous null mutation in the RYR1 gene in a consanguineous kindred with recurrent LMPS pregnancies. Resequencing of RYR1 in a cohort of 66 unrelated probands with FADS/LMPS/EVMPS (36 with FADS/LMPS and 30 with EVMPS) revealed two additional homozygous mutations (in frame deletions). The overall frequency of RYR1 mutations in probands with FADS/LMPS was 8.3%. Our findings report, for the first time, a homozygous RYR1 null mutation and expand the range of RYR1-related phenotypes to include early lethal FADS/LMPS. We suggest that RYR1 mutation analysis should be performed in cases of severe FADS/LMPS even in the absence of specific histopathological indicators of RYR1-related disease.

Is Webbing (Pterygia) a Constant Feature in Patients with Escobar Syndrome?

We describe two unrelated patients aged 9 and 12 years. The first patient presented with multiple congenital contractures not associated with webbing (pterygia). Interestingly, his genetic testing showed the typical genotypic criteria of Escobar syndrome (CHRNG heterozygous mutation). The characteristics of the second child were compatible with the phenotypic and genotypic criteria for Escobar syndrome. Both patients manifested the typical facial features suggestive of Escobar syndrome. The aim of this paper is twofold: first, to illustrate that the absence of popliteal webbing is not a sufficient reason to exclude Escobar syndrome in patients with multiple contractures and second, dysmorphic facial features and the presence of certain radiological abnormalities might be considered baseline diagnostic tools in favor of this syndromic entity.

P.12.8 The results of aerobic exercise program in Escobar syndrome: A case report

Escobar Syndrome is an autosomal recessive malformation which is characterized with growth retardation, multiple pterygia (neck, fingers, antecubital, popliteal? and intercrural areas), craniofacial anomalies. There are limited studies about effects of physical therapy in Escobar Syndrome in literature. 13 years old girl with Escobar Syndrome is taken in 8 week exercise program. She has short stature, scoliosis, neck pterygia, flat expressionless face, small mouth and micrognathia. Myometer is used to evaluate strength of 10 muscle group in lower extremities. North Star Ambulation Assessment (NSAA) and Six Minute Walk Test (6MWT) were performed to evaluate ambulation and performance. Timed Performance Test (TPT) also was applied for 12 activities. Aerobic exercise using arm and leg ergometer and stretching exercises were done 3 days in a week supervised by physiotherapist. Evaluation parameters were repeated after physiotherapy. After exercise program, 10 m walk, rising from floor, 4 steps ascending durations were shorter and standing on right and left sides’ durations were longer. Hip, knee and elbow muscles’ strength were improved. NSAA score rose from 24 to 31 and 6MWT distance increased from 440 to 484. Improvements in performance after exercise training show us that physical therapy is proper treatment option in Escobar Syndrome.

P.9.14 Next generation sequencing provides diagnosis for multiple foetal akinesia disorders

Whole exome sequencing (WES) permits cost effective causative mutation identification in highly heterogeneous diseases. Foetal akinesia/hypokinesia (the absence of or decreased movement in utero) is one disease group where WES is revolutionising patient diagnosis. The aim of this study was to identify the genetic cause of disease in a cohort of patients presenting with foetal akinesia and/or arthrogryposis. The first family in which causative variants were identified consisted of two siblings diagnosed with non-lethal multiple pterygium syndrome. WES of the proband revealed two novel mutations in a recently identified (Jan 2013) disease gene (ECEL1) causing distal arthrogryposis (DA) type 5D; a missense mutation (c.1531G>A; p.Gly511Ser) and a splice site mutation (c.1797-1G>A). Further investigations confirmed that the mutations co-segregated with disease. The clinical features of the siblings are in keeping with the described clinical picture for DA5D. The second family presented with Freeman-Sheldon syndrome (DA2A). WES of this proband revealed a known mutation in MYH3 (c.2015G>A; p.Arg672His). Sanger sequencing suggests the mutation likely arose de novo as neither of the parents carried the mutation. A third family presented with two consecutive pregnancies showing limited foetal movement, polyhydramnios, oedema and camptodactlyly. Muscle biopsy showed occasional cores and minicores. WES of the proband revealed two novel RYR1 variants: c.2455C>T; p.Arg819∗ and c.5989G>A; p.Glu1997Lys, as well as a novel TPM3 variant (c.502C>G; p.Leu168Val). The pathogenic significance of the apparent double trouble is yet to be clarified. This study exemplifies the capabilities of WES in the diagnoses of cases of foetal akinesia and arthrogryposis. It also highlights apparent “double trouble” which is likely to be recognized more as the use of WES becomes more widespread. In many other probands we did not identify causative mutations indicating perhaps the limitations of WES.

P.12.7 Swallowing evaluation in Escobar syndrome : A case report

Escobar syndrome is a rare disease characterized by multiple ptergia, skin webs and congenital anomalies like craniofacial defects, vertebral anomalies, cleft palate, kyphosis and scoliosis. Despite the passage of the disease is reported as an autosomal recessive, autosomal dominant and X-linked lethal multiple pterygium syndromes have also been reported in the literature. We aimed to discuss the swallowing physiology of a case who referred with swallowing disorders. Our case was 20 months old, male, 75 cm height and 10.5 kg weight and he fed by oral way. He was followed by 2.5 months with tracheostomy tube. He had pulmonary infection history once a month. Swallowing disorder was thought to be the cause of pulmonary infection so the swallowing evaluation was performed. Modified Barium Swallowing Evaluation was performed and the penetration aspiration scale (PAS) was used to define the aspiration severity. Delay in swallowing reflex (2–5 s) was determined. Silent aspiration was seen in liquid consistency with bottle feeding. The PAS score was 7. Oral intake with liquid thickener was recommended because swallowing evaluation showed that the cause of infections was liquid aspiration. Our results showed that swallowing disabilities should also be considered in this syndrome characterized by multiple congenital anomalies and necessary referral should be done in the early period.

Neuromotor synapses in Escobar syndrome

The Escobar variant of multiple pterygium syndrome (OMIM #265000) is a rare, autosomal recessive disorder associated with mutations in the γ-subunit of the nicotinic acetylcholine receptor (CHRNG). CHRNG is expressed in fetal muscle during motor development and contributes to the formation of neuromuscular junctions (NMJs). Anomalies in NMJ structure and function have not been investigated in patients with Escobar syndrome. We report five patients identified as having Escobar syndrome, from four families. In three families, the same mutation (c.459dupA) was identified in CHRNG. A biopsy from brachioradialis muscle was collected from a patient from one of these families and analyzed for NMJ organization using fluorescence microscopy. Compared to spinalis muscle from control patients with idiopathic scoliosis or cerebral palsy (CP), the patient with Escobar syndrome had a significantly higher degree of acetylcholine receptor present outside acetylcholinesterase and significantly less acetylcholinesterase outside acetylcholine receptors. Given the role of the acetylcholine receptor γ-subunit in fetal neuromuscular signal transduction and in establishing the primary encounter of muscle and motor nerve terminal, the CHRNG mutations described in Escobar syndrome may cause a broader disruption of postsynaptic proteins and result in aberrant development of the NMJ due to impaired prenatal neuromuscular transmission and/or abnormal neuromuscular synaptogenesis.

Clinical phenotype and the lack of mutations in the CHRNG, CHRND, and CHRNA1 genes in two Indian families with Escobar syndrome

The objective of this study was to report the clinical phenotype and genetic analysis of two Indian families with Escobar syndrome (ES). The diagnosis of ES in both families was made on the basis of published clinical features. Blood samples were collected from members of both families and used in genomic DNA isolation. The entire coding regions and intron-exon junctions of the ES gene CHRNG (cholinergic receptor, nicotinic, gamma), and two other related genes, CHRND and CHRNA1, were amplified and sequenced to search for mutations in both families. Both families show a typical form of ES. Sequencing of the entire coding regions including the intron-exon junctions of the three genes did not yield any mutations in these families. In conclusion, it is possible that the mutations in these genes are located in the promoter or deep intronic regions that we failed to identify or the ES in these families is caused by mutations in a different gene. The lack of mutations in CHRNG has also been reported in several families, suggesting the possibility of at least one more gene for this syndrome.

Novel deletion of lysine 7 expands the clinical, histopathological and genetic spectrum of TPM2-related myopathies

The β-tropomyosin gene encodes a component of the sarcomeric thin filament. Rod-shaped dimers of tropomyosin regulate actin-myosin interactions and β-tropomyosin mutations have been associated with nemaline myopathy, cap myopathy, Escobar syndrome and distal arthrogryposis types 1A and 2B. In this study, we expand the allelic spectrum of β-tropomyosin-related myopathies through the identification of a novel β-tropomyosin mutation in two clinical contexts not previously associated with β-tropomyosin. The first clinical phenotype is core-rod myopathy, with a β-tropomyosin mutation uncovered by whole exome sequencing in a family with autosomal dominant distal myopathy and muscle biopsy features of both minicores and nemaline rods. The second phenotype, observed in four unrelated families, is autosomal dominant trismus-pseudocamptodactyly syndrome (distal arthrogryposis type 7; previously associated exclusively with myosin heavy chain 8 mutations). In all four families, the mutation identified was a novel 3-bp in-frame deletion (c.20_22del) that results in deletion of a conserved lysine at the seventh amino acid position (p.K7del). This is the first mutation identified in the extreme N-terminus of β-tropomyosin. To understand the potential pathogenic mechanism(s) underlying this mutation, we performed both computational analysis and in vivo modelling. Our theoretical model predicts that the mutation disrupts the N-terminus of the α-helices of dimeric β-tropomyosin, a change predicted to alter protein-protein binding between β-tropomyosin and other molecules and to disturb head-to-tail polymerization of β-tropomyosin dimers. To create an in vivo model, we expressed wild-type or p.K7del β-tropomyosin in the developing zebrafish. p.K7del β-tropomyosin fails to localize properly within the thin filament compartment and its expression alters sarcomere length, suggesting that the mutation interferes with head-to-tail β-tropomyosin polymerization and with overall sarcomeric structure. We describe a novel β-tropomyosin mutation, two clinical-histopathological phenotypes not previously associated with β-tropomyosin and pathogenic data from the first animal model of β-tropomyosin-related myopathies.

Phosphorylation of Dishevelled by Protein Kinase RIPK4 Regulates Wnt Signaling

Receptor-interacting protein kinase 4 (RIPK4) is required for epidermal differentiation and is mutated in Bartsocas-Papas syndrome. RIPK4 binds to protein kinase C, but its signaling mechanisms are largely unknown. Ectopic RIPK4, but not catalytically inactive or Bartsocas-Papas RIPK4 mutants, induced accumulation of cytosolic β-catenin and a transcriptional program similar to that caused by Wnt3a. In Xenopus embryos, Ripk4 synergized with coexpressed Xwnt8, whereas Ripk4 morpholinos or catalytic inactive Ripk4 antagonized Wnt signaling. RIPK4 interacted constitutively with the adaptor protein DVL2 and, after Wnt3a stimulation, with the co-receptor LRP6. Phosphorylation of DVL2 by RIPK4 favored canonical Wnt signaling. Wnt-dependent growth of xenografted human tumor cells was suppressed by RIPK4 knockdown, suggesting that RIPK4 overexpression may contribute to the growth of certain tumor types.

Airway management in Escobar syndrome: A formidable challenge

Escobar syndrome is a rare autosomal recessive disorder characterized by flexion joint and digit contractures, skin webbing, cleft palate, deformity of spine and cervical spine fusion. Associated difficult airway is mainly due to micrognathia, retrognathia, webbing of neck and limitation of the mouth opening and neck extension. We report a case of a 1 year old child with Escobar syndrome posted for bilateral hamstrings to quadriceps transfer. The child had adequate mouth opening with no evidence of cervical spine fusion, yet we faced difficulty in intubation which was ultimately overcome by securing a proseal laryngeal mask airway (PLMA) and then by intubating with an endotracheal tube railroaded over a paediatric fibreoptic bronchoscope passed through the lumen of a PLMA.

Intrinsic Gating Energy of Fetal-Type Neuromuscular Acetylcholine Receptors

Fetal-type neuromuscular AChRs are composed of (α1)2βδγ subunits, whereas adult-type have the stoichiometry (α1)2βδe. γ-AChRs are indispensable for functional synapse formation, and mutations in this receptor subtype have been associated with congenital myasthenia, multiple pterygium syndrome and premature death. Cellular responses to transmitter molecules are influenced by a receptor's unliganded gating energy, G0. In mouse e-AChRs, G0=+8.4 kcal/mol (−100 mV). We estimated this intrinsic gating energy in γ-AChRs (single-channels, HEK cells), from measurements of the unliganded gating equilibrium constant E0 (G0=-0.59lnE0). E0 was extrapolated from observed E0 values in γ-AChRs having different combinations of background mutations that increased constitutive activity. First, 12 different background mutations were characterized separately (by measuring the diliganded gating equilibrium constant with choline) and were found to alter only G0 and not the energy from the agonist. The effects of the mutations in γ-AChRs were approximately the same as in e-AChRs. The extrapolation was based on two assumptions, that the change in the diliganded gating equilibrium constant (E2) is caused by only an equivalent change in G0, and that the G0 changes are independent. A log-log plot of E0obs vs. E2mut/E2wt resulted in straight line with slope 1.08±0.09, validating the two assumptions. From the extrapolation, E0wt,γ = 4.8×10−8, or G0wt,γ =+9.9 kcal/mol. This value is ∼+1.5 kcal/mol larger than e-AChR value. The inherent ‘slower' kinetics of γ- vs. e-AChRs may, in part, be attributed to the elevated intrinsic energy barrier of the gating transition state. The results are discussed in the light of a MWC thermodynamic cycle, to derive other equilibrium and kinetic parameters for γ-AChRs. This works lays the foundation for understanding the fetal-type AChR transmitter binding site.

Whole exome sequencing in foetal akinesia expands the genotype–phenotype spectrum of GBE1 glycogen storage disease mutations

The clinically and genetically heterogenous foetal akinesias have low rates of genetic diagnosis. Exome sequencing of two siblings with phenotypic lethal multiple pterygium syndrome identified compound heterozygozity for a known splice site mutation (c.691+2T>C) and a novel missense mutation (c.956A>G; p.His319Arg) in glycogen branching enzyme 1 (GBE1). GBE1 mutations cause glycogen storage disease IV (GSD IV), including a severe foetal akinesia sub-phenotype. Re-investigating the muscle pathology identified storage material, consistent with GSD IV, which was confirmed biochemically. This study highlights the power of exome sequencing in genetically heterogeneous diseases and adds multiple pterygium syndrome to the phenotypic spectrum of GBE1 mutation.

Prenatal Diagnosis of Lethal Multiple Pterygium Syndrome Using Two-and Three-Dimensional Ultrasonography

Lethal multiple pterygium (LMP) is a series of disorders of fetal formation with a heterogeneous range of manifestations that generally include cystic hygroma, pulmonary hypoplasia, cleft palate, cryptorchidism, joint contractures, fetal akinesia, heart defects, growth restriction, and intestinal malrotation. The prenatal diagnosis of this syndrome is suspected when two-dimensional ultrasound (2DUS) scan shows several malformations.. The three-dimensional ultrasound (3DUS) in rendering mode permits the spatial visualization of these malformations, allowing better understanding of this anomaly by parents. We report a case of a fetus in the second trimester with multiple abnormalities suggestive of LMP that were identified using 2DUS, and emphasize the importance of 3DUS in counseling the parents.

Zebrafish model for congenital myasthenic syndrome reveals mechanisms causal to developmental recovery

Mutations in muscle ACh receptors cause slow-channel syndrome (SCS) and Escobar syndrome, two forms of congenital myasthenia. SCS is a dominant disorder with mutations reported for all receptor subunits except γ. Escobar syndrome is distinct, with mutations located exclusively in γ, and characterized by developmental improvement of muscle function. The zebrafish mutant line, twister, models SCS in terms of a dominant mutation in the α subunit (α(twi)) but shows the behavioral improvement associated with Escobar syndrome. Here, we present a unique electrophysiological study into developmental improvement for a myasthenic syndrome. The embryonic α(twi)βδγ receptor isoform produces slowly decaying synaptic currents typical of SCS that transit to a much faster decay upon the appearance of adult ε, despite the α(twi) mutation. Thus, the continued expression of α(twi) into adulthood is tolerated because of the ε expression and associated recovery, raising the likelihood of unappreciated myasthenic cases that benefit from the γ-ε switch.

C.P.16 Mutations in the β-tropomyosin (TPM2) and γ-tropomyosin (TPM3) genes causing a spectrum of neuromuscular disorders

Published case reports of mutations in the tropomyosin genes describe a variety of neuromuscular disorders. The tropomyosins (Tms) exist as coiled-coil homo- or heterodimers forming head-to-tail polymers, running along the length of the actin molecule. They are encoded by four different genes; αTm (TPM1), βTm (TPM2), γTm (TPM3), and δTm (TPM4), generating more than 40 different tropomyosin isoforms. The tropomyosin genes TPM1, TPM2 and TPM3 are expressed in skeletal muscle encoding isoforms αTmfast, βTm, and δTmslow respectively. We extend the mutational and clinical spectrum of disorders caused by mutations of the β-tropomyosin (TPM2) and γ-tropomyosin (TPM3) genes and provide an overview of new and published cases. The clinical and histological findings of patients with cap myopathy, nemaline myopathy, CFTD, DA1A, DA2B and Escobar syndrome are correlated to the patients’ genotypes. We have also characterized the phosphorylation pattern of β-tropomyosin, both wt and β-tropomyosins containing patient mutations, and identified four novel phosphorylation sites.