We measured endogenous phosphorylation of peak II (apparent molecular weight of 220,000 daltons) of the erythrocyte membrane in 21 mothers of patients with Duchenne muscular dystrophy. The mean values of mothers with affected sons were significantly increased over those of matched controls (77.0 and 55.8 pmoles per milligram of 15-minute incubation; P less than 0.01). Detailed testing of mothers of affected sons revealed proximal muscle weakness. Seven mothers of isolated patients who had normal levels of creatine phosphokinase and no daughters with elevated levels were identified as carriers, because their mean value of peak II phosphorylation was increased (75.9 pmoles per milligram per 15 minutes) and equivalent to the level demonstrated in the 14 acknowledged carriers. Our results suggest that cases of Duchenne muscular dystrophy previously considered to be new mutations are much less common than estimated.

Female relatives of 41 Duchenne muscular dystrophy proband cases were studied with a panel of carrier-detection tests. A total of 277 relatives were tested in order to determine which mothers had affected sons as a result of new mutation. In 39 of 41 pedigrees the data demonstrate that a mutation cannot be postulated; the 2 megative pedigrees were inadequately tested. Our data suggest that all mothers of affected sons should be considered genetic carriers (heterozygotes) until proved otherwise. Our findings also raise questions concerning what mechanisms skew the indirect statistical estimates of mutation that are in common use.

Thirty mothers of patients with Duchenne muscular dystrophy were studied with serum enzyme tests, including serum glutamic-oxaloacetic transminase, creatine kinase, and lactate dehydrogenase isoenzymes. In addition, females from the mothers' pedigrees were studied. Lactate dehydrogenase isoenzyme 5 determinations were as senitive an indicator of carrier status as creatine kinase and also identified several mothers who had normal dehydrogenase isoenzyme 5 determinations, as well as extensive pedigree testing, identified 28 to 30 mothers as probable heterozygotes. These data independently support the suggestion that cases of Duchenne muscular dystrophy as a result of spontaneous mutation are more uncommon than currently accepted.

The application of recombinant DNA techniques applied to the study of genetic neurological diseases will play a major role in the practice of neurology in upcoming years. Strategies are now available to develop useful and relatively simple biochemical diagnostic tests for heterozygous individuals with diseases inherited as autosomal dominant traits. In addition, molecular genetic methods will lead to the delineation of the genomic mutations responsible for these diseases. This review will update the current status of research in several neurological genetic diseases including myotonic muscular dystrophy, Huntington's disease, Charcot-Marie-Tooth disease and Duchenne muscular dystrophy (X-linked). An introduction and overview of the methodology is provided. Specific research strategies including random screening of libraries, chromosome walking, messenger RNA selection, and messenger RNA translation are described. These strategies are designed to provide heterozygote identification, prenatal diagnosis and gestational management, the development of rational therapies, and the understanding of the molecular basis of disease expression.