[Miyoshi distal muscular dystrophy (Miyoshi myopathy)].

We present an overview of autosomal recessive distal muscular dystrophy (ARDMD), including recent molecular genetic findings. ARDMD is often referred to as Miyoshi-type distal muscular dystrophy (MDMD) or Miyoshi myopathy (MM). The onset of MDMD occurs in early adulthood. Muscle atrophy is most dominant in distal leg muscles, especially the flexor muscles, i.e., gastrocnemius and soleus. As MDMD advances, muscle atrophy progresses to the thigh and hip muscles. Toe standing is impaired but heel standing can still be accomplished early in the disease course. This is followed by difficulty in standing and walking. The patients rarely become confined to bed. Serum creatine kinase level is markedly elevated, e.g., 100 times the upper limit of the normal range early in the disease course. Pre-symptomatic patients may also have high creatine kinase levels. Heterozygous individuals may have only slightly elevated creatine kinase levels. Recent development revealed that MDMD and LGMD2B are both caused by mutations in the dysferlin gene (DYSF). C1939G, G3370T, 3746delG, and 4870delT are reported to be common mutations among patients with MDMD. The dysferlin protein is presumably involved in the repair of muscle cell membranes. Among the patients reported originally by Miyoshi et al., 3 affected individuals from 3 different families were confirmed carriers of dysferlin mutations. Additionally, 1 heterozygous individual was identified. Although MDMD and LGMD2B are caused by the mutation of the same gene, ARDMD is characterized by initial involvement of leg flexors while LGMD2B is characterized by involvement of the proximal leg muscles. The difference in the distribution becomes obscure as the 2 diseases progress. The temporal profiles of functional impairment in the 2 diseases are reportedly very similar. When MDMD is suspected, it is important to carefully observe the relevant leg, more specially the flexor muscle group.