Increased turnover of muscle contractile proteins in Duchenne muscular dystrophy as assessed by 3-methylhistidine and creatinine excretion.

1. Myofibrillar protein degradation has been measured in patients with Duchenne muscular dystrophy, normal boys, adult males and Duchenne carriers by the rate of 3-methylhistidine excretion after transfer of subjects to a meat-free diet. 2. Although absolute rates of protein breakdown are lower in Duchenne patients, expression of the data to allow for differences in muscle mass gives fractional degradation rates 2--3 times higher than in age-matched controls. 3. Fractional rates of muscle protein synthesis are increased in the Duchenne patients to almost the same extent as protein breakdown. 4. Rates of muscle protein breakdown in obligate and presumed carriers of the Duchenne gene are not different from controls.