G.P.36 An autosomal dominant distal myopathy

Abstract

The distal myopathies are a clinically and pathologically heterogeneous group of genetic disorders in which the distal muscles of limbs are selectively or disproportionately affected. Until date, at least 20 genes have been shown to be involved in distal myopathy. A 26-year-old Chinese male presented with progressive weakness of distal limbs for 2years. His mother has the same symptoms. Neurological examination revealed wading gait, with no ataxia, predominantly distal limb weakness of four limbs was noticed. Sensory examination was unremarkable, no evidence of pyramidal tract signs. Serum creatine kinase was 656IU/l. Electrocardiogram test was normal. Nerve conduction study showed normal sensory and motor nerve conduction. Needle electromyography showed decreased amplitude and short-duration motor unit action potentials and some myotonic discharges in some tested muscles. MRI scans of his legs revealed significantly fatty infiltration of anterior tibial muscles. Muscle biopsy of anterior tibial muscle revealed degenerating and necrotic fibers and many rimmed vacuoles were observed; type-fibers are predominant; glycogen and lipid contents appear normal; anti-dysferlin immunohistochemical stain was normal. MYH7 gene and Mex5–6 region of the TTN gene were sequenced. No pathogenic variant was detected. The patients we reported with distal muscular dystrophy was of early adult onset and presumably inherited in an autosomal dominant inheritance. It was characterized by a selective involvement of anterior tibial muscle, finger extensors muscle, and neck extension muscles. Serum CK level was mildly elevated. Histopathological findings revealed autophagic vacuoles and normal expression of dysferlin protein. Laing distal myopathy or tibial muscular dystrophy (TMD) was suspected according clinic, electrophysiological, and pathological findings. But no pathogenic variant was detected in MYH7 gene and Mex5–6 region of th.