Myotonia With Skeletal Abnormalities And Mental Retardation

In 3 brothers and a sister out of 9 sibs of nonconsanguineous parents, Richieri-Costa et al. (1984) described a progressive disorder with onset usually at a mean age of 5.7 years and including myotonia, progressive impairment of gait, alterations in the thorax and vertebral column, short stature, and mild to moderate mental retardation. The 15-year-old proband had 'painful spasms' in his legs and a progressively rigid gait. He showed pectus carinatum and generalized muscular hypertrophy with a firm consistency. Both spontaneous and elicited myotonia was found. A wedge deformity of the first and second lumbar vertebra was demonstrated. The articular surfaces of the acetabulum and the femoral epiphyses were also irregular. His 13-year-old brother also had 'painful spasms,' pectus carinatum, pronounced muscular hypertrophy and firm consistency of muscles, and kyphoscoliosis. Their affected 20-year-old brother was only 139 cm tall. Wedge vertebra at the first and/or second lumbar level seemed to be a consistent feature. Richieri-Costa et al. (1984) pointed to the lack of blepharophimosis and small mouth and the presence of mental retardation as some of the features distinguishing this disorder from Schwartz-Jampel syndrome (255800). Furthermore, they pointed out that the Schwartz-Jampel syndrome usually starts in the first 2 years of life, whereas the initial manifestations were later in this disorder. (For some reason, however, they referred to the disorder as 'late infantile autosomal recessive myotonia' in the title of their article.)