To the Editor: We read with interest the report of Roses et al. (N Engl J Med 294:193, 1976). This contribution to an understanding of the carrier state in Duchenne muscular dystrophy may lead to more specific identification of the abnormality in membrane proteins and abnormal membrane permeability. However, the authors' conclusions about the underlying proportion of cases attributable to spontaneous mutation and to gene carriers need considerable clarification. They suggest that a balanced polymorphism with heterozygote advantage could maintain the deleterious gene at a high frequency. Such a polymorphism on the X chromosome would require the normal homozygote.
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