Carrier testing in families of isolated cases of duchenne muscular dystrophy. Creatine kinase activities in female relatives of mothers with normal CK activity

A study of the serum creatine kinase (CK) activity in the female relatives of mothers of isolated cases of Duchenne muscular dystrophy (DMD) was undertaken. It was restricted to the relatives of mothers with normal serum CK values. Ninety-eight females in 19 families were studied; none was found to have a serum CK activity more than 3 sd above the normal mean. This evidence, derived from a study in which the measurement of serum CK activity was used as the sole means of detecting carriers, suggests that very few distant female relatives in such families are carriers of the gene and provides some evidence against the hypothesis that mutation is a rare cause of isolated cases of Duchenne muscular dystrophy.