[Identification of Y chromosome material in an XX male by means of fluorescent in situ hybridization].

This article describes a case of 46,XX male, the most frequent form of sex reversal syndromes in humans. A method of identifying Y chromosome material in these and other patients with structural chromosomal abnormalities involving chromosome Y is given. Chromosomes from a phenotypically normal male child without any congenital malformation, where prenatal diagnosis revealed the female karyotype 46,XX, were analysed using fluorescence in situ hybridisation (FISH). The analysis revealed an X chromosome, containing Y chromosome sequences on the tip of the short arm. The sequences are not normally visible in conventional cytogenetic analyses of XX males. The breakpoint on Y was determined to be in the region of Yp11.2, which is proximal for the putative sex determining gene on Y. The results are consistent with theories of abnormal crossing-over during the paternal meiotic cell division where meiotic recombination can give rise to structural abnormalities, which can then cause sex reversal syndromes. Prenatal diagnosis of structural sex chromosome abnormalities has become available using the FISH method.