Detection of carriers of benign X-linked muscular dystrophy.

From the point of view of genetic counselling carrier detection is most important in X-linked disorders. Okinaka et al. (1959) were the first to employ the serum level of creatine kinase to detect female carriers of X-linked Duchenne muscular dystrophy. Since then many investigators have confirmed the usefulness and reliability of this test. So far results on over 200 carriers have been reported, and of these approximately two-thirds were found to have significantly raised levels of serum creatine kinase (Emery, 1967). Besides the severe Duchenne type of muscular dystrophy, another X-linked form of muscular dystrophy has been recognized by Becker (1955, 1957, 1962). This type of muscular dystrophy is clinically similar to Duchenne muscular dystrophy in that weakness begins in the pelvic girdle musculature, only later affecting the upper limbs, and there is pseudohypertrophy of the calf muscles. However, it differs from Duchenne muscular dystrophy because the disease does not manifest itself until the teens or early twenties, and affected individuals usually become chair-ridden only after 25 to 30 years. This report is concerned with the usefulness of serum enzyme studies for detecting carriers of this benign Becker type X-linked muscular dystrophy.