Congenital fiber-type disproportion myopathy with type I fiber predominance and type II fiber smallness and atrophy - A sterological analysis

Congenital myopathy with fiber-type disproportion is an established disorder, where type I fibers predominate with smallness of the same type. We report a family with three siblings (12-year-old boy, 9-year-old girl, and 6-year-old boy) with clinical features of congenital myopathy, where muscle biopsy in the eldest sib showed fiber-type disproportion. Type I fibers predominated with small and atrophic type II fibers which is unusual, especially when the child did not have any other clinical or biochemical abnormality to account for this type of variation. Further, a stereological analysis highlighted the differences with regards to number, size and even volume of the fiber types. A 3-dimensional concept is proposed for this morphological abnormality.