Late infantile autosomal recessive myotonia, mental retardation, and skeletal abnormalities: a new autosomal recessive syndrome.

Four sibs of non-consanguineous parents who had myotonia from late infancy are described. Mild to moderate mental retardation, severe bone abnormalities of the vertebral column (mainly in the thoracolumbar region), and short stature were also observed. Autosomal recessive inheritance is demonstrated. These cases are compared with reported cases of the Schwartz-Jampel syndrome.