Familial type I fiber atrophy.

An 11-year-old boy and his 40-year-old mother with congenital, non-progressive muscular weakness and wasting are described. Muscle biopsies from both cases showed a selective atrophy of Type I fibers without any structural change except for very few nemaline bodies. Probably, the neuromuscular disorder in this family is identical to the congenital fiber type disproportion described by Dubowitz and Brooke, but familial Type I fiber atrophy (hypotrophy, or hypoplasia) is considered to be a more appropriate descriptive term for a family with such distinct histochemical characteristics.