Limb Girdle Muscular Dystrophy due to Digenic Inheritance of DES and CAPN3 Mutations

We report the clinical and genetic analysis of a 63-year-old man with progressive weakness developing over more than 20 years. Prior to his initial visit, he underwent multiple neurological and rheumatological evaluations and was treated for possible inflammatory myopathy. He did not respond to any treatment that was prescribed and was referred to our center for another opinion. He underwent a neurological evaluation, electromyography, magnetic resonance imaging of his legs, and a muscle biopsy. All testing indicated a chronic myopathy without inflammatory features suggesting a genetic myopathy. Whole-exome sequencing testing more than 50 genes known to cause myopathy revealed variants in the COL6A3 (rs144651558), RYR1 (rs143445685), CAPN3 (rs138172448), and DES (rs144901249) genes. We hypothesized that the inheritance pattern could follow a digenic pattern of inheritance. Screening for these polymorphisms in an unaffected sister revealed the presence of all these same variants except for that in the CAPN3 gene. All variants were studied to determine their frequency and if they had been previously reported as mutations. They were also subjected to protein modeling programs, including SIFT, PolyPhen, and MutationTaster. This analysis indicated that the CAPN3 variant c.1663G>A (rs138172448), which results in a p.Val555Ile change, and the DES gene variant c.656C>T (rs144901249), which results in a p.Thr219Ile change, are both predicted to be damaging. These 2 variants were further investigated employing the STRING program that analyzes protein networks and pathways. This analysis provided further support for our hypothesis that these mutations in the CAPN3 and DES genes, through digenic inheritance, are the cause of the myopathy in this patient

Clinical and Genetic Analysis of an Asian Indian Family with Charcot-Marie-Tooth Disease Type 4C

Charcot-Marie-Tooth disease type 4C, an autosomal recessive genetic neuropathy, is caused by mutations in the SH3TC2 (SH3 domain and tetratricopeptide repeats 2) gene. Interestingly, although mutations in this gene have been observed in European gypsies, a population that originated in India, there are few publications describing Indian patients. We report our analysis of a 50-year-old woman of Asian Indian descent with onset of progressive distal weakness and sensory loss in childhood. A clinical examination revealed the presence of a neuropathy with pes cavus without spinal abnormalities. Electrophysiological testing confirmed a sensorimotor length-dependent neuropathy with demyelinating features. A genetic analysis revealed she carries 2 novel mutations, c.2488G>T variant (rs879254317) and c.731+5G>A variant (rs879254316), in the SH3TC2 gene. Further genetic testing demonstrated that her son is a carrier of the c.731+5G>A mutation. Our analysis confirms that this patient is a compound heterozygote inheriting these mutations, which are in trans, in an autosomal recessive pattern. Her son developed an episode of sciatic neuropathy with complete resolution. We hypothesize that in his case, haploinsufficiency caused by c.731+5G>A mutation may have predisposed him to the development of this focal neuropathy

Factors Affecting Phenotype Variability in a Family with CMT2B: Gender and LRSAM1 Genotype

Charcot-Marie-Tooth disease type 2 (CMT2) is an autosomal dominant axonal neuropathy caused by mutations in various genes. The subtype CMT2B results from missense mutations in RAB7A, member RAS oncogene family gene, whereas missense mutations in the Leucine-rich repeat and sterile alpha motif-containing protein 1 (LRSAM1) gene cause CMT2P. We describe the genotype/phenotype analysis of a family in which a previously described mutation in the RAB7A gene and a novel mutation in the LRSAM1 gene were identified. In this family, none of the individuals had ulceromutilating features, and there was a marked variability in the age of onset. We discuss the possible etiology of the observed phenotypic variability including the role of gender and possible RAB7A/LRSAM1 gene interactions