Brief clinical report: del(X) (q26) in a phenotypically normal woman and her daughter who also has trisomy 21.

We present a phenotypically normal woman with del(X)(q26) with no evidence of mosaicism, who had two pregnancies resulting in two live-born infants. Her first child had trisomy 21 Down syndrome and the del(X)(q26). To our knowledge, this woman is the first known case of presumably nonmosaic del(Xq) producing live-born infants. This finding can be explained on the basis of persistence into adulthood of germ cells in ovaries of the rare del(Xq) individuals. The normal phenotype in this woman supports the hypothesis that the absence of genes of middle Xq segment (q13 leads to q26) is responsible for the somatic manifestations of the Ullrich-Turner syndrome. Our finding suggests that prenatal diagnosis should be offered not only to pregnant women with numerical X chromosome abnormalities, as suggested previously, but also to those with structural X chromosome abnormalities, because of the possibility of chromosome aberrations in the offspring of such women.