Double aneuploidy in a Turkish child: Down-Klinefelter syndrome.

The occurrence of double aneuploidy in the one person is a relatively rare phenomenon. A 5-year-old child, the second-born of non-consanguineous parents, possessed an extra X chromosome in addition to trisomy 21. The proband's parents and his brother showed normal karyotype. The phenotypic characteristics of the child have been discussed in light of the published reports on double aneuploidies of XXY and trisomy 21.