women whose sisters’ sons had bled profusely whenthey were circumcised.Duchenne muscular dystrophyis a fatal X-linked re-cessive disease. The phenotype is a wasting and atrophyof muscles. Generally the onset is before the age of 6,with conﬁnement to a wheelchair by 12, and death by20. The gene for Duchenne muscular dystrophy has nowbeen isolated and shown to encode the muscle proteindystrophin. This discovery holds out hope for a betterunderstanding of the physiology of this condition and,ultimately, a therapy.A rare X-linked recessive phenotype that is interest-ing from the point of view of sexual differentiation is acondition called testicular feminization syndrome,whichhas a frequency of about 1 in 65,000 male births. Peopleafﬂicted with this syndrome are chromosomally males,having 44 autosomes plus an X and a Y, but they de-velop as females (Figure 2-27). They have female exter-nal genitalia, a blind vagina, and no uterus. Testes may bepresent either in the labia or in the abdomen. Although
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