Generation of two iPSC lines from patients with inherited central core disease and concurrent malignant hyperthermia caused by dominant missense variants in the RYR1 gene.

RYR1 variants are the most common genetic cause of congenital myopathies, and typically cause central core disease (CCD) and/or malignant hyperthermia (MH). Here, we generated iPSC lines from two patients with CCD and MH caused by dominant RYR1 variants within the central region of the protein (p.Val2168Met and p.Arg2508Cys). Both lines displayed typical iPSC morphology, uniform expression of pluripotency markers, trilineage differentiation potential, and had normal karyotypes. These are the first RYR1 iPSC lines from patients with both CCD and MH. As these are common CCD/MH variants, these lines should be useful to study these conditions and test therapeutics.

Loss-of-function variants in JPH1 cause congenital myopathy with prominent facial involvement.

Background: Weakness of facial, ocular, and axial muscles is a common clinical presentation in congenital myopathies caused by pathogenic variants in genes encoding triad proteins. Abnormalities in triad structure and function resulting in disturbed excitation-contraction coupling and Ca 2+ homeostasis can contribute to disease pathology. Methods: We analysed exome and genome sequencing data from three unrelated individuals with congenital myopathy characterised by striking facial, ocular, and bulbar involvement. We collected deep phenotypic data from the affected individuals. We analysed the RNA-seq data of one proband and performed gene expression outlier analysis in 129 samples. Results: The three probands had remarkably similar clinical presentation with prominent facial, ocular, and bulbar features. Disease onset was in the neonatal period with hypotonia, poor feeding, cleft palate and talipes. Muscle weakness was generalised but most prominent in the lower limbs with facial weakness also present. All patients had myopathic facies, bilateral ptosis, ophthalmoplegia and fatiguability. While muscle biopsy on light microscopy did not show any obvious morphological abnormalities, ultrastructural analysis showed slightly reduced triads, and structurally abnormal sarcoplasmic reticulum. DNA sequencing identified three unique homozygous loss of function variants in JPH1 , encoding junctophilin-1 in the three families; a stop-gain (c.354C>A; p.Tyr118*) and two frameshift (c.373del p.Asp125Thrfs*30 and c.1738del; p.Leu580Trpfs*16) variants. Muscle RNA-seq showed strong downregulation of JPH1 in the F3 proband. Conclusions: Junctophilin-1 is critical to the formation of skeletal muscle triad junctions by connecting the sarcoplasmic reticulum and T-tubules. Our findings suggest that loss of JPH1 results in a congenital myopathy with prominent facial, bulbar and ocular involvement. Key message: This study identified novel homozygous loss-of-function variants in the JPH1 gene, linking them to a unique form of congenital myopathy characterised by severe facial and ocular symptoms. Our research sheds light on the critical impact on junctophilin-1 function in skeletal muscle triad junction formation and the consequences of its disruption resulting in a myopathic phenotype. What is already known on this topic: Previous studies have shown that pathogenic variants in genes encoding triad proteins lead to various myopathic phenotypes, with clinical presentations often involving muscle weakness and myopathic facies. The triad structure is essential for excitation-contraction (EC) coupling and calcium homeostasis and is a key element in muscle physiology. What this study adds and how this study might affect research practice or policy: This study establishes that homozygous loss-of-function mutations in JPH1 cause a congenital myopathy predominantly affecting facial and ocular muscles. This study also provides clinical insights that may aid the clinicians in diagnosing similar genetically unresolved cases.

Ablation of the carboxy-terminal end of MAMDC2 causes a distinct muscular dystrophy.

The extracellular matrix (ECM) has an important role in the development and maintenance of skeletal muscle, and several muscle diseases are associated with the dysfunction of ECM elements. MAMDC2 is a putative ECM protein and its role in cell proliferation has been investigated in certain cancer types. However, its participation in skeletal muscle physiology has not been previously studied. We describe 17 individuals with an autosomal dominant muscular dystrophy belonging to two unrelated families in which different heterozygous truncating variants in the last exon of MAMDC2 co-segregate correctly with the disease. The radiological aspect of muscle involvement resembles that of COL6 myopathies with fat replacement at the peripheral rim of vastii muscles. In this cohort, a subfascial and peri-tendinous pattern is observed in upper and lower limb muscles. Here we show that MAMDC2 is expressed in adult skeletal muscle and differentiating muscle cells, where it appears to localize to the sarcoplasm and myonuclei. In addition, we show it is secreted by myoblasts and differentiating myotubes into to the extracellular compartment. The last exon encodes a disordered region with a polar residue compositional bias loss of which likely induces a toxic effect of the mutant protein. The precise mechanisms by which the altered MAMDC2 proteins cause disease remains to be determined. MAMDC2 is a skeletal muscle disease-associated protein. Its role in muscle development and ECM-muscle communication remains to be fully elucidated. Screening of the last exon of MAMDC2 should be considered in patients presenting with autosomal dominant muscular dystrophy, particularly in those with a subfascial radiological pattern of muscle involvement.

Expanding the phenotype of DNMT3A as a cause a congenital myopathy with rhabdomyolysis.

Pathogenic variants in DNMT3A are most commonly associated with Tatton-Brown-Rahman Syndrome (TBRS), but includes other phenotypes such as Heyn-Sproul-Jackson syndrome and acute myeloid leukemia (AML). We describe a patient presenting to the neuromuscular clinic with a de novo missense variant in DNMT3A where the striking clinical feature is that of a congenital myopathy with associated episodes of rhabdomyolysis, severe myalgias and chest pain along with phenotypic features associated with TBRS. Muscle biopsy showed minor myopathic features and cardiac investigations revealed mildly impaired bi-ventricular systolic function. We confirmed the DNA methylation profile matched haplo-insufficient TBRS cases, consistent with a loss of methyltransferase activity. Our report emphasizes the phenotypic overlap of patients with syndromic disorders presenting to neuromuscular clinics and limitations of gene panels in establishing a molecular diagnosis.

Transcriptome and Genome Analysis Uncovers a DMD Structural Variant: A Case Report.

Objective: Duchenne muscular dystrophy (DMD) is caused by pathogenic variants in the dystrophin gene (DMD). Hypermethylated CGG expansions within DIP2B 5' UTR are associated with an intellectual development disorder. Here, we demonstrate the diagnostic utility of genomic short-read sequencing (SRS) and transcriptome sequencing to identify a novel DMD structural variant (SV) and a DIP2B CGG expansion in a patient with DMD for whom conventional diagnostic testing failed to yield a genetic diagnosis. Methods: We performed genomic SRS, skeletal muscle transcriptome sequencing, and targeted programmable long-read sequencing (LRS). Results: The proband had a typical DMD clinical presentation, autism spectrum disorder (ASD), and dystrophinopathy on muscle biopsy. Transcriptome analysis identified 6 aberrantly expressed genes; DMD and DIP2B were the strongest underexpression and overexpression outliers, respectively. Genomic SRS identified a 216 kb paracentric inversion (NC_000023.11: g.33162217-33378800) overlapping 2 DMD promoters. ExpansionHunter indicated an expansion of 109 CGG repeats within the 5' UTR of DIP2B. Targeted genomic LRS confirmed the SV and genotyped the DIP2B repeat expansion as 270 CGG repeats. Discussion: Here, transcriptome data heavily guided genomic analysis to resolve a complex DMD inversion and a DIP2B repeat expansion. Longitudinal follow-up will be important for clarifying the clinical significance of the DIP2B genotype.

Loss of function variants in DNAJB4 cause a myopathy with early respiratory failure.

DNAJ/HSP40 co-chaperones are integral to the chaperone network, bind client proteins and recruit them to HSP70 for folding. We performed exome sequencing on patients with a presumed hereditary muscle disease and no genetic diagnosis. This identified four individuals from three unrelated families carrying an unreported homozygous stop gain (c.856A > T; p.Lys286Ter), or homozygous missense variants (c.74G > A; p.Arg25Gln and c.785 T > C; p.Leu262Ser) in DNAJB4. Affected patients presented with axial rigidity and early respiratory failure requiring ventilator support between the 1st and 4th decade of life. Selective involvement of the semitendinosus and biceps femoris muscles was seen on MRI scans of the thigh. On biopsy, muscle was myopathic with angular fibers, protein inclusions and occasional rimmed vacuoles. DNAJB4 normally localizes to the Z-disc and was absent from muscle and fibroblasts of affected patients supporting a loss of function. Functional studies confirmed that the p.Lys286Ter and p.Leu262Ser mutant proteins are rapidly degraded in cells. In contrast, the p.Arg25Gln mutant protein is stable but failed to complement for DNAJB function in yeast, disaggregate client proteins or protect from heat shock-induced cell death consistent with its loss of function. DNAJB4 knockout mice had muscle weakness and fiber atrophy with prominent diaphragm involvement and kyphosis. DNAJB4 knockout muscle and myotubes had myofibrillar disorganization and accumulated Z-disc proteins and protein chaperones. These data demonstrate a novel chaperonopathy associated with DNAJB4 causing a myopathy with early respiratory failure. DNAJB4 loss of function variants may lead to the accumulation of DNAJB4 client proteins resulting in muscle dysfunction and degeneration.

A KLHL40 3' UTR splice-altering variant causes milder NEM8, an under-appreciated disease mechanism.

Nemaline myopathy 8 (NEM8) is typically a severe autosomal recessive disorder associated with variants in the kelch-like family member 40 gene (KLHL40). Common features include fetal akinesia, fractures, contractures, dysphagia, respiratory failure and neonatal death. Here, we describe a 26-year-old man with relatively mild NEM8. He presented with hypotonia and bilateral femur fractures at birth, later developing bilateral Achilles' contractures, scoliosis, and elbow and knee contractures. He had walking difficulties throughout childhood and became wheelchair bound from age 13 after prolonged immobilization. Muscle magnetic resonance imaging at age 13 indicated prominent fat replacement in his pelvic girdle, posterior compartments of thighs and vastus intermedius. Muscle biopsy revealed nemaline bodies and intranuclear rods. RNA sequencing and western blotting of patient skeletal muscle indicated significant reduction in KLHL40 mRNA and protein, respectively. Using gene panel screening, exome sequencing and RNA sequencing, we identified compound heterozygous variants in KLHL40; a truncating 10.9 kb deletion in trans with a likely pathogenic variant (c.*152G > T) in the 3' untranslated region (UTR). Computational tools SpliceAI and Introme predicted the c.*152G > T variant created a cryptic donor splice site. RNA-seq and in vitro analyses indicated that the c.*152G > T variant induces multiple de novo splicing events that likely provoke nonsense mediated decay of KLHL40 mRNA explaining the loss of mRNA expression and protein abundance in the patient. Analysis of 3' UTR variants in ClinVar suggests variants that introduce aberrant 3' UTR splicing may be underrecognized in Mendelian disease. We encourage consideration of this mechanism during variant curation.

Identification of a novel heterozygous DYSF variant in a large family with a dominantly-inherited dysferlinopathy.

AIMS: Dysferlinopathy is an autosomal recessive muscular dystrophy, caused by bi-allelic variants in the gene encoding dysferlin (DYSF). Onset typically occurs in the second to third decade and is characterised by slowly progressive skeletal muscle weakness and atrophy of the proximal and/or distal muscles of the four limbs. There are rare cases of symptomatic DYSF variant carriers. Here, we report a large family with a dominantly inherited hyperCKaemia and late-onset muscular dystrophy. METHODS AND RESULTS: Genetic analysis identified a co-segregating novel DYSF variant [NM_003494.4:c.6207del p.(Tyr2070Metfs*4)]. No secondary variants in DYSF or other dystrophy-related genes were identified on whole genome sequencing and analysis of the proband's DNA. Skeletal muscle involvement was milder and later onset than typical dysferlinopathy presentations; these clinical signs manifested in four individuals, all between the fourth and sixth decades of life. All individuals heterozygous for the c.6207del variant had hyperCKaemia. Histological analysis of skeletal muscle biopsies across three generations showed clear dystrophic signs, including inflammatory infiltrates, regenerating myofibres, increased variability in myofibre size and internal nuclei. Muscle magnetic resonance imaging revealed fatty replacement of muscle in two individuals. Western blot and immunohistochemical analysis of muscle biopsy demonstrated consistent reduction of dysferlin staining. Allele-specific quantitative PCR analysis of DYSF mRNA from patient muscle found that the variant, localised to the extreme C-terminus of dysferlin, does not activate post-transcriptional mRNA decay. CONCLUSIONS: We propose that this inheritance pattern may be underappreciated and that other late-onset muscular dystrophy cases with mono-allelic DYSF variants, particularly C-terminal premature truncation variants, may represent dominant forms of disease.

FXR1-related congenital myopathy: expansion of the clinical and genetic spectrum.

BACKGROUND: Biallelic pathogenic variants in FXR1 have recently been associated with two congenital myopathy phenotypes: a severe form associated with hypotonia, long bone fractures, respiratory insufficiency and infantile death, and a milder form characterised by proximal muscle weakness with survival into adulthood. OBJECTIVE: We report eight patients from four unrelated families with biallelic pathogenic variants in exon 15 of FXR1. METHODS: Whole exome sequencing was used to detect variants in FXR1. RESULTS: Common clinical features were noted for all patients, which included proximal myopathy, normal serum creatine kinase levels and diffuse muscle atrophy with relative preservation of the quadriceps femoris muscle on muscle imaging. Additionally, some patients with FXR1-related myopathy had respiratory involvement and required bilevel positive airway pressure support. Muscle biopsy showed multi-minicores and type I fibre predominance with internalised nuclei. CONCLUSION: FXR1-related congenital myopathy is an emerging entity that is clinically recognisable. Phenotypic variability associated with variants in FXR1 can result from differences in variant location and type and is also observed between patients homozygous for the same variant, rendering specific genotype-phenotype correlations difficult. Our work broadens the phenotypic spectrum of FXR1-related congenital myopathy.

The genetic landscape of axonal neuropathies in the middle-aged and elderly: Focus on MME.

OBJECTIVE: To test the hypothesis that monogenic neuropathies such as Charcot-Marie-Tooth disease (CMT) contribute to frequent but often unexplained neuropathies in the elderly, we performed genetic analysis of 230 patients with unexplained axonal neuropathies and disease onset ≥35 years. METHODS: We recruited patients, collected clinical data, and conducted whole-exome sequencing (WES; n = 126) and MME single-gene sequencing (n = 104). We further queried WES repositories for MME variants and measured blood levels of the MME-encoded protein neprilysin. RESULTS: In the WES cohort, the overall detection rate for assumed disease-causing variants in genes for CMT or other conditions associated with neuropathies was 18.3% (familial cases 26.4%, apparently sporadic cases 12.3%). MME was most frequently involved and accounted for 34.8% of genetically solved cases. The relevance of MME for late-onset neuropathies was further supported by detection of a comparable proportion of cases in an independent patient sample, preponderance of MME variants among patients compared to population frequencies, retrieval of additional late-onset neuropathy patients with MME variants from WES repositories, and low neprilysin levels in patients' blood samples. Transmission of MME variants was often consistent with an incompletely penetrant autosomal-dominant trait and less frequently with autosomal-recessive inheritance. CONCLUSIONS: A detectable fraction of unexplained late-onset axonal neuropathies is genetically determined, by variants in either CMT genes or genes involved in other conditions that affect the peripheral nerves and can mimic a CMT phenotype. MME variants can act as completely penetrant recessive alleles but also confer dominantly inherited susceptibility to axonal neuropathies in an aging population.

NEMF mutations that impair ribosome-associated quality control are associated with neuromuscular disease.

A hallmark of neurodegeneration is defective protein quality control. The E3 ligase Listerin (LTN1/Ltn1) acts in a specialized protein quality control pathway-Ribosome-associated Quality Control (RQC)-by mediating proteolytic targeting of incomplete polypeptides produced by ribosome stalling, and Ltn1 mutation leads to neurodegeneration in mice. Whether neurodegeneration results from defective RQC and whether defective RQC contributes to human disease have remained unknown. Here we show that three independently-generated mouse models with mutations in a different component of the RQC complex, NEMF/Rqc2, develop progressive motor neuron degeneration. Equivalent mutations in yeast Rqc2 selectively interfere with its ability to modify aberrant translation products with C-terminal tails which assist with RQC-mediated protein degradation, suggesting a pathomechanism. Finally, we identify NEMF mutations expected to interfere with function in patients from seven families presenting juvenile neuromuscular disease. These uncover NEMF's role in translational homeostasis in the nervous system and implicate RQC dysfunction in causing neurodegeneration.

Cylindrical spirals in two families: Clinical and genetic investigations.

Cylindrical spirals are a rare ultrastructural finding on muscle biopsy, with fewer than 20 reported cases since its first description in 1979. These structures are sometimes observed with tubular aggregates and are thought to comprise longitudinal sarcoplasmic reticulum. While mutations in genes encoding key components of Ca2+ handling (ORAI1 and STIM1) underlie tubular aggregate myopathy, no causative genes have been associated with cylindrical spirals. Here we describe two families with cylindrical spirals on muscle biopsy with a suspected genetic cause. In one family we identified a known truncating variant in EBF3, previously associated with a neurodevelopmental disorder. The affected individuals in this family present with clinical features overlapping with those described for EBF3 disease. An isolated proband in the second family harbours bi-allelic truncating variants in TTN and her clinical course and other features on biopsy are highly concordant for titinopathy. From experimental studies, EBF3 is known to be involved in Ca2+ regulation in muscle, thus EBF3 dysregulation may represent a novel mechanism of impaired Ca2+ handling leading to cylindrical spirals. Additional cases of EBF3 disease or titinopathy with cylindrical spirals need to be identified to support the involvement of these genes in the pathogenesis of cylindrical spirals.

Systemic AAV8-mediated delivery of a functional copy of muscle glycogen phosphorylase (Pygm) ameliorates disease in a murine model of McArdle disease.

McArdle disease is a disorder of carbohydrate metabolism that causes painful skeletal muscle cramps and skeletal muscle damage leading to transient myoglobinuria and increased risk of kidney failure. McArdle disease is caused by recessive mutations in the muscle glycogen phosphorylase (PYGM) gene leading to absence of PYGM enzyme in skeletal muscle and preventing access to energy from muscle glycogen stores. There is currently no cure for McArdle disease. Using a preclinical animal model, we aimed to identify a clinically translatable and relevant therapy for McArdle disease. We evaluated the safety and efficacy of recombinant adeno-associated virus serotype 8 (rAAV8) to treat a murine model of McArdle disease via delivery of a functional copy of the disease-causing gene, Pygm. Intraperitoneal injection of rAAV8-Pygm at post-natal day 1-3 resulted in Pygm expression at 8 weeks of age, accompanied by improved skeletal muscle architecture, reduced accumulation of glycogen and restoration of voluntary running wheel activity to wild-type levels. We did not observe any adverse reaction to the treatment at 8 weeks post-injection. Thus, we have investigated a highly promising gene therapy for McArdle disease with a clear path to the ovine large animal model endemic to Western Australia and subsequently to patients.

Recessive MYH7-related myopathy in two families.

Myopathies due to recessive MYH7 mutations are exceedingly rare, reported in only two families to date. We describe three patients from two families (from Australia and the UK) with a myopathy caused by recessive mutations in MYH7. The Australian family was homozygous for a c.5134C > T, p.Arg1712Trp mutation, whilst the UK patient was compound heterozygous for a truncating (c.4699C > T; p.Gln1567*) and a missense variant (c.4664A > G; p.Glu1555Gly). All three patients shared key clinical features, including infancy/childhood onset, pronounced axial/proximal weakness, spinal rigidity, severe scoliosis, and normal cardiac function. There was progressive respiratory impairment necessitating non-invasive ventilation despite preserved ambulation, a combination of features often seen in SEPN1- or NEB-related myopathies. On biopsy, the Australian proband showed classical myosin storage myopathy features, while the UK patient showed multi-minicore like areas. To establish pathogenicity of the Arg1712Trp mutation, we expressed mutant MYH7 protein in COS-7 cells, observing abnormal mutant myosin aggregation compared to wild-type. We describe skinned myofiber studies of patient muscle and hypertrophy of type II myofibers, which may be a compensatory mechanism. In summary, we have expanded the phenotype of ultra-rare recessive MYH7 disease, and provide novel insights into associated changes in muscle physiology.

Biallelic mutations in nucleoporin NUP88 cause lethal fetal akinesia deformation sequence.

Nucleoporins build the nuclear pore complex (NPC), which, as sole gate for nuclear-cytoplasmic exchange, is of outmost importance for normal cell function. Defects in the process of nucleocytoplasmic transport or in its machinery have been frequently described in human diseases, such as cancer and neurodegenerative disorders, but only in a few cases of developmental disorders. Here we report biallelic mutations in the nucleoporin NUP88 as a novel cause of lethal fetal akinesia deformation sequence (FADS) in two families. FADS comprises a spectrum of clinically and genetically heterogeneous disorders with congenital malformations related to impaired fetal movement. We show that genetic disruption of nup88 in zebrafish results in pleiotropic developmental defects reminiscent of those seen in affected human fetuses, including locomotor defects as well as defects at neuromuscular junctions. Phenotypic alterations become visible at distinct developmental stages, both in affected human fetuses and in zebrafish, whereas early stages of development are apparently normal. The zebrafish phenotypes caused by nup88 deficiency are rescued by expressing wild-type Nup88 but not the disease-linked mutant forms of Nup88. Furthermore, using human and mouse cell lines as well as immunohistochemistry on fetal muscle tissue, we demonstrate that NUP88 depletion affects rapsyn, a key regulator of the muscle nicotinic acetylcholine receptor at the neuromuscular junction. Together, our studies provide the first characterization of NUP88 in vertebrate development, expand our understanding of the molecular events causing FADS, and suggest that variants in NUP88 should be investigated in cases of FADS.

Bi-allelic mutations in MYL1 cause a severe congenital myopathy.

Congenital myopathies are typically characterised by early onset hypotonia, weakness and hallmark features on biopsy. Despite the rapid pace of gene discovery, ∼50% of patients with a congenital myopathy remain without a genetic diagnosis following screening of known disease genes. We performed exome sequencing on two consanguineous probands diagnosed with a congenital myopathy and muscle biopsy showing selective atrophy/hypotrophy or absence of type II myofibres. We identified variants in the gene (MYL1) encoding the skeletal muscle fast-twitch specific myosin essential light chain (ELC) in both probands. A homozygous essential splice acceptor variant (c.479-2A > G, predicted to result in skipping of exon 5 was identified in Proband 1, and a homozygous missense substitution (c.488T>G, p.(Met163Arg)) was identified in Proband 2. Protein modelling of the p.(Met163Arg) substitution predicted it might impede intermolecular interactions that facilitate binding to the IQ domain of myosin heavy chain, thus likely impacting on the structure and functioning of the myosin motor. MYL1 was markedly reduced in skeletal muscle from both probands, suggesting that the missense substitution likely results in an unstable protein. Knock down of myl1 in zebrafish resulted in abnormal morphology, disrupted muscle structure and impaired touch-evoked escape responses, thus confirming that skeletal muscle fast-twitch specific myosin ELC is critical for myofibre development and function. Our data implicate MYL1 as a crucial protein for adequate skeletal muscle function and that MYL1 deficiency is associated with severe congenital myopathy.

Mutations in ATP1A1 Cause Dominant Charcot-Marie-Tooth Type 2.

Although mutations in more than 90 genes are known to cause CMT, the underlying genetic cause of CMT remains unknown in more than 50% of affected individuals. The discovery of additional genes that harbor CMT2-causing mutations increasingly depends on sharing sequence data on a global level. In this way-by combining data from seven countries on four continents-we were able to define mutations in ATP1A1, which encodes the alpha1 subunit of the Na+,K+-ATPase, as a cause of autosomal-dominant CMT2. Seven missense changes were identified that segregated within individual pedigrees: c.143T>G (p.Leu48Arg), c.1775T>C (p.Ile592Thr), c.1789G>A (p.Ala597Thr), c.1801_1802delinsTT (p.Asp601Phe), c.1798C>G (p.Pro600Ala), c.1798C>A (p.Pro600Thr), and c.2432A>C (p.Asp811Ala). Immunostaining peripheral nerve axons localized ATP1A1 to the axolemma of myelinated sensory and motor axons and to Schmidt-Lanterman incisures of myelin sheaths. Two-electrode voltage clamp measurements on Xenopus oocytes demonstrated significant reduction in Na+ current activity in some, but not all, ouabain-insensitive ATP1A1 mutants, suggesting a loss-of-function defect of the Na+,K+ pump. Five mutants fall into a remarkably narrow motif within the helical linker region that couples the nucleotide-binding and phosphorylation domains. These findings identify a CMT pathway and a potential target for therapy development in degenerative diseases of peripheral nerve axons.

Expanding the phenotypic spectrum associated with mutations of DYNC1H1.

Autosomal dominant mutations of DYNC1H1 cause a range of neurogenetic diseases, including mental retardation with cortical malformations, hereditary spastic paraplegia and spinal muscular atrophy. Using SNP array, linkage analysis and next generation sequencing, we identified two families and one isolated proband sharing a known spinal muscular atrophy, lower extremity predominant (SMALED) causing mutation DYNC1H1 c.1792C>T, p.Arg598Cys, and another family harbouring a c.2327C>T, p.Pro776Leu mutation. Here, we present a detailed clinical and pathological examination of these patients, and show that patients with DYNC1H1 mutations may present with a phenotype mimicking a congenital myopathy. We also highlight features that increase the phenotypic overlap with BICD2, which causes SMALED2. Serial muscle biopsies were available for several patients, spanning from infancy and early childhood to middle age. These provide a unique insight into the developmental and pathological origins of SMALED, suggesting in utero denervation with reinnervation by surrounding intact motor neurons and segmental anterior horn cell deficits. We characterise biopsy features that may make diagnosis of this condition easier in the future.

Lethal multiple pterygium syndrome: A severe phenotype associated with a novel mutation in the nebulin gene.

Fetal akinesia deformation sequence is a clinically and genetically heterogeneous disorder characterized by a variable combination of fetal akinesia, intrauterine growth restriction, developmental abnormalities such as cystic hygroma, hydrops fetalis, pulmonary hypoplasia, occasional arthrogryposis, and pterygia. The pathogenetic mechanisms of fetal akinesia deformation sequence include neuropathy, muscular disorders, neuromuscular junction disorders, maternal myasthenia gravis, restrictive dermopathy and others. We here report an Egyptian family presenting with recurrent lethal multiple pterygium syndrome. The diagnosis was based on antenatal sonographic demonstration of complete fetal akinesia and a large cystic hygroma with severe limb contractures evident on postmortem examination. Next generation sequencing performed on the second affected fetus identified a novel homozygous essential splice-site variant in the nebulin gene. In conclusion, our report adds further evidence for the involvement of the nebulin gene in the etiology of fetal akinesia deformation sequence/lethal multiple pterygium syndrome.

Recurrent de novo BICD2 mutation associated with arthrogryposis multiplex congenita and bilateral perisylvian polymicrogyria.

Autosomal dominantly inherited mutations of BICD2 are associated with congenital-onset spinal muscular atrophy characterised by lower limb predominance. A few cases have also showed upper motor neuron pathology, including presenting with features resembling hereditary spastic paraplegia. The age-of-onset for the published families is usually at birth but also included cases with childhood- and adult-onset disease. In this report we described two isolated probands that presented in utero with features associated with reduced fetal movements. Both cases were diagnosed at birth with arthrogryposis multiplex congenita (AMC) and hypotonia. Other variable features included congenital fractures, hip dislocation, micrognathia, respiratory insufficiency, microcephaly and bilateral perisylvian polymicrogyria. Patient 1 is 4 years of age and stable, but shows significant motor developmental delay and delayed speech. Patient 2 passed away at 7 weeks of age. Through next generation sequencing we identified the same missense substitution in BICD2 (p.Arg694Cys) in both probands. Sanger sequencing showed that in both cases the mutation arose de novo. The in utero onset in both cases suggests that the p.Arg694Cys substitution may have a more deleterious effect on BICD2 function than previously described mutations. Our results broaden the phenotypes associated with BICD2 mutations to include AMC and cortical malformations and therefore to a similar phenotypic spectrum to that associated with its binding partner DYNC1H1.