Congenital fiber type disproportion: report of one case.

Congenital fiber type disproportion (CFTD) is described clinically as muscle weakness and hypotonia with delayed motor development, usually from infancy. Muscle biopsy reveals that type 1 fibers predominate and smaller than type 2 fibers by a margin greater than 12% of the diameter of the type 2 fibers. There are no other subcellular abnormalities, and generally prognosis is good. The CFTD case is a six-month-old girl who manifested clinically as a floppy infant. A biopsied specimen from the left biceps brachii muscle revealed type 1 fiber predominance and hypoplasia with an increased number of undifferentiated type 2C fibers. Electromyogram, nerve conduction velocity and serum creatine kinase level were normal. The child learned to walk without assistance at 1 year 7 month old. Now 2-years and 10-months old, she can climb stairs without difficulty, although she cannot run fast.