[MIM*251900] weakness and hypotonia of muscles, primarily those of the neck, shoulder, and pelvic girdles, with onset in infancy or childhood; on biopsy, giant bizarre mitochondria are seen located between muscle fibrils just beneath the sarcolemma. There are autosomal dominant [MIM*251900] and recessive forms due to deletions or duplications of mitochondrial DNA, with one recessive form [MIM*252010] associated with a deficiency of complex I of the mitochondrial respiratory chain.