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Skeletal muscle growth and regeneration rely on muscle stem cells, called satellite cells. Specific transcription factors, particularly PAX7, are key regulators of the function of these cells. Knockout of this factor in mice leads to poor postnatal survival; however, the consequences of a lack of PAX7 in humans have not been established. Purpose Skeletal muscle growth and regeneration rely on muscle stem cells, called satellite cells. Specific transcription factors, particularly PAX7, are key regulators of the function of these cells. Knockout of this factor in mice leads to poor postnatal survival; however, the consequences of a lack of PAX7 in humans have not been established. Methods Here, we study five individuals with myopathy of variable severity from four unrelated consanguineous couples. Exome sequencing identified pathogenic variants in the PAX7 gene. Clinical examination, laboratory tests, and muscle biopsies were performed to characterize the disease. Results The disease was characterized by hypotonia, ptosis, muscular atrophy, scoliosis, and mildly dysmorphic facial features. The disease spectrum ranged from mild to severe and appears to be progressive. Muscle biopsies showed the presence of atrophic fibers and fibroadipose tissue replacement, with the absence of myofiber necrosis. A lack of PAX7 expression was associated with satellite cell pool exhaustion; however, the presence of residual myoblasts together with regenerating myofibers suggest that a population of PAX7-independent myogenic cells partially contributes to muscle regeneration. Conclusion These findings show that biallelic variants in the master transcription factor PAX7 cause a new type of myopathy that specifically affects satellite cell survival., German Bundesministerium für Bildung und Forschung through the Juniorverbund in der Systemmedizin “mitOmics” (FKZ01ZX1405C to T.B.H.) and Horizon2020 through the E-Rare project GENOMIT (01GM1603 and 01GM1207 for H.P. and FWFI2741B26 for J.A.M.) and the Deutsche Forschungsgemeinschaft (SCHO754/52 to L.S. and BA2427/22 to P.B.) as well as the Vereinigung zur Förderung Pädiatrischer Forschung und Fortbildung Salzburg, the EU FP7 Mitochondrial European Educational Training Project (317433 to H.P. and J.A.M.), and the EU Horizon2020 Collaborative Research Project SOUND (633974 to H.P.). N.A.D. is supported by grants from the Fonds de recherche du Québec–Santé (35015), Canadian Institutes of Health Research (388296), Rare Disease Foundation (2301), and CHU Sainte-Justine Foundation. N.A.D. acknowledges the support of ThéCell and Stem Cell Networ

Hereditary myopathies are progressive muscle disorders caused by a wide range of different genetic defects. Very few causal therapeutic options are available in clinical practice. However, major advances in basic science and an improved pathophysiological understanding have led to several new therapeutic options for hereditary myopathies. New therapeutic strategies based on molecular genetics, like stop codon read-through using the agent PTC124 or exon-skipping through antisense-oligonucleotides, are currently being tested in clinical trials in patients with Duchenne muscular dystrophy. However, uncoordinated and incomplete clinical testing of new treatments often delays the progress from bench to bedside. Well planned and coordinated clinical trials are therefore desirable and in some cases already in the planning stage. Here, we summarise current pharmacotherapeutic treatment options for patients with hereditary myopathies, like the use of corticosteroids, growth factors and dietary supplements, and supportive treatment options.

Effective planning of clinical trials requires an appropriate number of patients who fulfil given inclusion criteria. In the case of so called “orphan” diseases, such as Duchenne and Becker muscular dystrophy (DMD/BMD), the number of suitable patients within one country is usually limited. We developed a detailed registry of Czech and Slovak DMD/BMD patients which may contribute to cooperation on the European level. The registry uses internet and database technologies with a multilevel architecture. Patients may view their own data. As of May 2008, 163 patients have been registered in the database. The registry provides a detailed phenotypic and genotypic description of patients. The main purpose of such a registry is the time-effective recruitment of eligible patients for a clinical trial or therapy and may allow the anticipation of possible future effects of appropriate therapy on individual patients. The importance of the DMD/BMD patient registries has recently also been rising with new clinical trials focused on mutation-specific approaches. Other outputs include assessment of epidemiology, phenotype and genotype relationships, or standards of care.

The patient reported here presented with first symptoms at the age of 10 showing an abnormal gait, calf hypertrophy and winged scapulae. She was diagnosed with eosinophilic myositis after muscle biopsy. A second muscle biopsy at the age of 20 and subsequent genetic testing, however, revealed the underlying condition of a primary gamma-sarcoglycanopathy, or LGMD2C. To our knowledge, this is the first LGMD2C patient reported who initially presented with eosinophilic myositis. Eosinophilia has been reported previously in patients with Calpainopathy and Becker Muscular Dystrophy and might be an early, but transient feature of a wider range of muscular dystrophies.

Objective: Congenital myasthenic syndromes (CMS) with underlying RAPSN mutations turned out to be of high clinical relevance due to their worldwide frequency. To date, all reported patients with CMS with sequence variations in the translated region of RAPSN carry the mutation N88K on at least one allele. The authors report two patients lacking the common N88K allele but harboring differing novel mutations of the RAPSN gene on both alleles: one patient is homozygous for a missense mutation (R164C); the second patient is compound heterozygous for a splice (IVS1-15C>A) and another missense mutation (L283P). Methods: The authors analyzed the RAPSN gene for sequence variations and carried out in vitro studies in order to delineate the potential pathogenicity of the three novel RAPSN mutations. Results: For the putative splice mutation (IVS1-15C>A), the authors constructed wild-type and mutated RAPSN minigenes for transfection and subsequent RNA analysis. The mutation generates a novel acceptor splice site leading to retention of 13 nucleotides of intron 1 in the mature mRNA and subsequently to a frameshift transcript. Cotransfection of wild-type AChR subunits with RAPSN- constructs carrying R164C and L283P indicate that both mutations diminish coclustering of AChR with rapsyn. Conclusions: Screening for the common mutation RAPSN N88K facilitates targeted genetic analysis in congenital myasthenic syndromes. However, absence of a N88K allele does not exclude underlying RAPSN mutations as cause of the congenital myasthenic syndromes. Sequencing of the entire gene may be considered in patients with joint contractures and respiratory problems even in the absence of the mutation N88K.

The objective of this study was to analyse the mutations of the acetylcholine receptor (AChR) delta subunit gene ( CHRND ) in a patient with sporadic congenital myasthenic syndrome (CMS). Mutations in various genes encoding proteins expressed at the neuromuscular junction may cause CMS. Mutations of AChR subunit genes lead to end-plate AChR deficiency or to altered kinetic properties of the receptor. Mutations in the alpha, beta and delta subunits of the AChR are less frequent than mutations of the epsilon subunit; mutations in these subunits leading to AChR deficiency are often associated with a severe phenotype. A sporadic patient from Germany was studied, who presented with an early onset CMS associated with feeding difficulties, ptosis, a moderate general weakness responsive to anticholinesterase treatment and recurrent episodes of respiratory insufficiency provoked by infections. The CHRND gene was screened for mutations by RFLP, long-range PCR and sequence analysis. Subsequently, we conducted functional studies of AChR mutants co-transfected with rapsyn in HEK 293 cells. Heterozygously to a 2.2 kb microdeletion disrupting the CHRND gene, we identified a novel point mutation in the long cytoplasmic loop, CHRND E381K. The cytoplasmic loop of the AChR subunits is known to be essential for AChR–rapsyn co-clustering. We therefore studied the interaction of AChR containing the CHRND E381K mutation with rapsyn by evaluating expression and co-localization of rapsyn and mutated AChR subunits in co-transfected HEK 293 cells. Interestingly, the mutated receptor showed severely reduced cluster formation compared with the wild-type receptor. In contrast, the corresponding amino acid substitution in the cytoplasmic loop of the AChR epsilon ( CHRNE E376K) as well as a recently reported CMS mutation affecting this domain ( CHRNE N436del) had no impact on cluster formation. CHRND mutations are a rare cause for CMS but should be considered in patients with a severe, early onset disease form, clinically resembling a rapsyn phenotype with recurrent episodic apnoeas. Our results suggest that impairment of AChR–rapsyn co-clustering—a well-known molecular mechanism for rapsyn mutations—could also result from mutations in the delta subunit. Introduction of the same mutation in the epsilon subunit had no effect on AChR clustering indicating a special role of the delta subunit in AChR–rapsyn interactions.

Only recently, mutations of the RAPSN gene have been recognised as causing acetylcholine receptor deficiency at the motor endplate resulting in early and late onset forms of congenital myasthenic syndromes (CMS).1–9 In most studies a single missense mutation of RAPSN (N88K) was detected either homozygously or compound heterozygously in numerous, unrelated patients of European and North American origin. Based on the analysis of a small number of intragenic single nucleotide polymorphisms (SNPs) and/or extragenic, polymorphic repeat markers, we hypothesised that RAPSN (N88K) may derive from a common founder.7 However, this hypothesis was disputed in a recent report in the Journal of Medical Genetics.10 In this study, 12 independent RAPSN (N88K) alleles from white North American CMS patients were compared to 37 wild type chromosomes. Five intragenic SNPs and two extragenic microsatellite markers appeared to be in linkage disequilibrium with the mutation, whereas four extragenic microsatellite markers failed to prove a significant association.10 To resolve this question we analysed 41 independent RAPSN (N88K) alleles using 21 SNPs flanking RAPSN on chromosome 11p11.11 We collected 21 CMS patients harbouring RAPSN (N88K) either homozygously (n = 20) or compound heterozygously (n = 1). Screening for the mutation N88K (264C→A) in exon 2 of the RAPSN gene was performed as described previously.7 Patients originated from Germany (n = 5), Austria (n = 1), Italy (n = 1), France (n = 2), the United Kingdom (n = 10), and the Indian subcontinent (n = 2). Consanguinity was not reported for any of the families. Most of the patients have been described, previously: patients G1–G4, Au1, UK10, and It1 (patients 1–7 in Muller et al 7), patients UK1–7 (patients 3, 9, 11, 12, 13, 15, and 16 in Burke et al 6), patient Ind2 (patient 1 in Burke et al 6), patient Fr1 (patient 1 in Richard et al 8), and patient Fr2 (in Yasaki …

Congenital myasthenic syndromes (CMS) with deficiency of end' plate acetylcholinesterase (AChE) are caused by mutations in the synapse specific collagenic tail subunit gene (COLQ) of AChE. We identified a novel missense mutation (T441A) homozygously in three CMS patients from two unrelated German families. The mutation is located in the C-terminal region of the ColQ protein, which initiates assembly of the triple helix, and is essential for insertion of the tail subunit into the basal lamina. Density gradient analysis of AChE extracted from muscle of one of the patients revealed the absence of asymmetric AChE. All patients were characterized by an onset of disease in childhood, exercise-induced proximal weakness, absence of ptosis and ophthalmoparesis, a decremental EMG response, and deterioration in response to anticholinesterase drugs. However, age at onset, disease progression, disease severity, and functional impairment varied considerably among the three patients. As adults, two siblings from one family experience only mild impairment, while the third patient requires a wheelchair for most of the day and assisted ventilation at night.