A Study of Creatine Metabolism in Diseases Causing Muscle Wasting *

Abstract

The half-time of the decrease in urinary creatinine specific activity after an intravenous injection of creatine-1-C14 was 38 days in a subject with normal muscle function; 39 days in a patient with amyotrophic lateral sclerosis; 49 days in a patient with a myopathy of late onset; 13, 14, and 21 days in patients with Duchenne muscular dystrophy; and 23 days in a patient with facioscapulohumeral muscular dystrophy. Skeletal muscle creatine specific activity was similar to that of urinary creatinine at several time intervals. Thus the disappearance of radioactive urinary creatinine reflects the disappearance of radioactive creatine from muscle. The isotope content of urinary creatine and/or its rate of change was identical to that of urinary creatinine in the patients with Duchenne muscular dystrophy. These findings indicate that muscle is unable to retain creatine normally in Duchenne muscular dystrophy.