Congenital myopathies.

The evaluation of the "floppy infant" is a common problem for neurologists who deal with infants. One major category of diseases to consider in the diagnosis of hypotonia in the infant is the congenital myopathies. The congenital myopathies are a group of nonprogressive primary diseases of muscle that present in infancy with hypotonia and weakness and that are subdivided on the basis of the morphologic characteristics seen on histochemical study of the muscle. These diseases share many clinical features despite demonstrating a wide range of variation. Through the study of the various congenital myopathies, considerable knowledge of the structural components of the muscle fiber and their function has been gained. Despite this, our understanding of these conditions is incomplete at this time.