Creatine-phosphokinase (CPK) activity in relatives of patients with X-linked muscular dystrophies: a Brazilian study.

Serum CPK was measured in 135 families with Duchenne muscular dystrophy (DMD) and 19 with the Becker type (BMD). Increased CPK was found in 62% of the carriers of DMD and 62.5% of the BMD. Two certain carries of DMD and one of their daughters showed clinical signs of myopathy. Three studied DMD pregnant carriers suggest that there is a decrease in CPK levels around the 4th-5th months of gestation. In genetic counselling of suspected carriers the CPK activity of their normal daughters should always be considered. Our data suggest strongly that CPK activity decreases in carriers with increasing age.