In an extensive epidemiological survey of Duchenne muscular dystrophy carried out in Venetia (Italy) the incidence was found to be 28.2×10-5 and female gamete mutation rate was estimated by the direct method between 61 and 35×10-6. The percentage of isolated cases was 0.54. Indirect and direct estimates of this proportion suggest, however, that only a minor fraction arises from maternal mutation (from 0.11 to 0.18 of the total number of cases). Studies on pedigrees collected in the course of the survey indicate that there is a higher frequency of Duchenne carrier females than normal females in affected sibships. Additional evidence supporting the hypothesis of a reproductive heterozygote advantage and gametic selection is reported.
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