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Background: Fetal akinesia/hypokinesia, arthrogryposis and severe congenital myopathies are heterogeneous conditions usually presenting before or at birth. Although numerous causative genes have been identified for each of these disease groups, in many cases a specific genetic diagnosis remains elusive. Due to the emergence of next generation sequencing, virtually the entire coding region of an individual's DNA can now be analysed through "whole" exome sequencing, enabling almost all known and novel disease genes to be investigated for disorders such as these., Methods: Genomic DNA samples from 45 patients with fetal akinesia/hypokinesia, arthrogryposis or severe congenital myopathies from 38 unrelated families were subjected to next generation sequencing. Clinical features and diagnoses for each patient were supplied by referring clinicians. Genomic DNA was used for either whole exome sequencing or a custom-designed neuromuscular sub-exomic supercapture array containing 277 genes responsible for various neuromuscular diseases. Candidate disease-causing variants were investigated and confirmed using Sanger sequencing. Some of the cases within this cohort study have been published previously as separate studies., Results: A conclusive genetic diagnosis was achieved for 18 of the 38 families. Within this cohort, mutations were found in eight previously known neuromuscular disease genes (CHRND, CHNRG, ECEL1, GBE1, MTM1, MYH3, NEB and RYR1) and four novel neuromuscular disease genes were identified and have been published as separate reports (GPR126, KLHL40, KLHL41 and SPEG). In addition, novel mutations were identified in CHRND, KLHL40, NEB and RYR1. Autosomal dominant, autosomal recessive, X-linked, and de novo modes of inheritance were observed., Conclusions: By using next generation sequencing on a cohort of 38 unrelated families with fetal akinesia/hypokinesia, arthrogryposis, or severe congenital myopathy we therefore obtained a genetic diagnosis for 47% of families. This study highlights the power and capacity of next generation sequencing (i) to determine the aetiology of genetically heterogeneous neuromuscular diseases, (ii) to identify novel disease genes in small pedigrees or isolated cases and (iii) to refine the interplay between genetic diagnosis and clinical evaluation and management.

Abstract: Foetal akinesia/hypokinesia is an absence or decrease of movement in utero resulting in a spectrum of anomalies characterised by intrauterine growth retardation, contractures, craniofacial anomalies, limb anomalies, pulmonary hypoplasia and polyhydramnios. Despite a large number of disease genes (>30) being associated with this heterogenous group of disorders, the majority of cases are without a genetic diagnosis. The aim of this study was to investigate the use of whole exome sequencing (WES) to identify the causative gene/s in a preliminary set of four families with foetal akinesia. In three families presenting with foetal akinesia and nemaline bodies, all the known nemaline myopathy genes were excluded by WES. The fourth family presented with lethal multiple pterygium syndrome. WES of DNA from two affected sibs revealed compound heterozygous mutations in the glycogen branching enzyme-1 gene (GBE1): a known splice site mutation (c.691+2T>C) and a novel missense mutation (c.956A>G; p.His319Arg) at a highly conserved residue. Each parent carried one of the mutations. GBE1 mutations are known to cause glycogen storage disease IV (GSD IV), a subset of which present with a severe neuromuscular foetal akinesia phenotype. In light of the genetic findings, the muscle pathology was reviewed and PAS positive, diastase resistant faintly refractile material was observed, consistent with GSD IV. Our data highlight that novel nemaline myopathy gene/s remain to be identified and that WES can be used successfully for the diagnosis of foetal akinesias. This study expands the genotype–phenotype correlation of GBE1 mutations: (1) since GSD IV should now be considered in cases presenting as lethal multiple pterygium syndrome and (2) since the vast majority of known foetal akinesia GSD IV cases are due to large indels or frameshift mutations and it is generally considered that the type of the mutations corresponds with clinical severity. [Copyright &y& Elsevier]