Clinically manifesting carriers in Duchenne muscular dystrophy.

Three manifesting carriers of Duchenne muscular dystrophy were examined clinically and histologically. All had muscle weakness in the upper and lower limbs without facial muscle involvement, onset being at the ages of 35, 19 and 25 years, respectively. Pseudohypertrophy of calves was evident in all cases. Biochemical, electrocardiographic and histological observations revealed the presence of myopathy in all cases. Sex chromatin patterns were normal. Compared with the manifesting carriers previously reported by others, at least one case showed more severe histological findings which were typical of the advanced stage of Duchenne muscular dystrophy. The cardiac involvement in three cases was moderate. A possible involvement of other factors besides Lyonization influencing the development of myopathy in the carriers is suggested.