The manifesting carrier in Duchenne muscular dystrophy

Twenty‐two female carriers of Duchenne muscular dystrophy (DMD) presenting with myopathic symptoms have been examined. Eleven were definite carriers, aged 29 to 79 years, and 11 were possible carriers, aged 4 to 57 years. There was considerable variation in the clinical manifestations and the course of the myopathy, which in many cases resembled the autosomal recessive limb girdle type of muscular dystrophy (LGMD). Serum levels of creatine kinase were significantly greater in manifesting carriers than in non‐manifesting carriers of DMD and female patients with LGMD. Ten out of the 22 manifesting carriers were familial cases, being either sisters or mother and daughter(s). The frequency of clinical manifestations among female first degree relatives of myopathic DMD carriers is significantly greater than would be expected from the observed prevalence of manifestations among definite carriers (7.8 %). The prevalence of manifesting DMD carriers in the general female population was estimated to be 22.4 × 10 ‐6 , which is comparable to the 19.9 × 10 ‐6 prevalence for LGMD. The differential diagnosis between the two conditions and the pathogenetic aspects with regard to Lyon's hypothesis and to additional, possibly genetic regulatory mechanisms, are discussed.