Congenital fibre type disproportion myopathy. A histological diagnosis with an uncertain clinical outlook.

Nine children with congenital fibre type disproportion (CFTD) are described. Their muscle biopsies contained type 1 fibres which were smaller than the largest type 2 fibres by at least 13.5%. Attention is drawn to the variable natural history of this disorder which generally carries a good prognosis but may sometimes be associated with fatal respiratory problems. For important therapeutic, genetic, and prognostic reasons CFTD must be distinguished from other conditions with similar histochemical or clinical features.