Résumé :
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Laing early-onset distal myopathy (MPD1) is an autosomal dominant myopathy due to mutations within the slow skeletal muscle fibre myosin heavy chain, MYH7. We report the phenotype of a French family with four affected individuals on two generations. The mode of inheritance was autosomal dominant. Disease onset was in infancy. The first symptoms were pes planus, frequent falls or poor sportive performances. The clinical findings were homogeneous and included distal lower limb weakness in anterior compartment muscles (4/4), distal upper limb weakness in finger extensors (3/4), Achilles tendon retraction (4/4), pes plano-valgus (4/4), lumbar hyperlordosis (3/4) and kyphoscoliosis (3/4). Neck flexors were preserved. The progression was very slow. The functional disability in adulthood was limited to fatigability, calf cramps, ankle instability for lower limbs, and weakness of finger extension for upper limbs. There were no sensory abnormalities. Electromyographic examination showed a myogenic pattern in two patients and a mixed neurogenic and myogenic pattern in the two others. Motor and sensory conduction were normal. Muscle biopsy performed in anterior tibialis muscle in the propositus when he was 8 years old revealed type 1 fibres smallness and fibres with centralized nuclei. Genetic analysis showed a not previously reported heterozygous Glu1508Del mutation in the MYH7 gene.
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