Muscular Dystrophy (duchenne) in a Girl with Turner's Syndrome.

According to classical genetics, a recessive sex-linked or X-linked gene manifests its existence phenotypically only in the absence of its normal allele, that is, in the homozygous state or in the absence of a second X chromosome carrying the normal allele. The latter requirement is met, for instance, in males who have haemophilia as a sex-linked trait: they have only one X chromosome in their XY chromosome complement. In females with the usual XX sex-chromosome composition a gene such as the haemophilia gene is not able to manifest itself, as it is neutralized by the presence of its normal allele on the second X. The situation is different in XO females: as in XY males, all recessive genes carried by the single X chromosome can freely express themselves. The case reported here is that of a girl with Turner's syndrome and Duchenne type muscular dystrophy. Chromatin negative Turner's syndrome is usually the consequence of a complete or partial (mosaic) XO sex-chromosome complement. Duchenne type muscular dystrophy usually appears to be sex-linked (Morton, Chung, and Peters, I963; Boyer and Fainer, I963; Walton, I964). The present case offers cytogenetical evidence in support of sex linkage and of a permissive effect of abnormal sex-chromosome complement with regard to muscular dystrophy.