Serum enzyme studies in muscle disease: Part III Serum creatine kinase activity in relatives of patients with the Duchenne type of muscular dystrophy

Abstract

Serum creatine kinase activity detection rate in 7 female known carriers was 71%, in 8 female probable carriers 62%, and in 35 female possible carriers 50%. An activity of more than 4.0 units strongly suggested a carrier. Of 23 cases examined, there were 6 cases of preclinical dystrophy detected in male sibs of patients with the disease. These 6 cases were young children who showed no detectable weakness, atrophy of pseudohypertrophy of the muscles. The results indicate that (1) it is possible to detect the majority of carriers by means of estimating the serum creatine kinase activity, and (2) this enzyme is of more value than other serum enzymes in the detection of the carrier state. It is hoped that the combined results of serum creatine kinase estimation and electromyographic studies will produce an even more accurate identification of carriers. In view of the Lyon hypothesis of female X-chromosome mosaicism, a dual population of muscle cells, one normal and one myopathic, may be present in the female carrier. A carrier with a preponderance of normal cells may show only a slight elevation in serum creatine knase activity whereas a carrier with a preponderance of mutant X-chromosomal cells may exhibit a high enzyme activity, abnormal muscle biopsy findings and clinical evidence of muscular weakness.