Analysis of sex chromosome distribution in the gonadal tissue of a 45,X/47,XYY mosaic by fluorescence in situ hybridization

45,X/47,XYY mosaicism is a rare condition with scarce information on the tissue-specific distribution of the different cell lines. Fluorescence in situ hybridization with repetitive, chromosome-specific DNA probes was applied to gain insight into the tissue-specific distribution of the two cell lines in biopsies of the streak gonad and dysgenetic testis of a 2-year-old individual exhibiting 45,X/47,XYY mosaicism. The distribution of the 45,X/47,XYY cells within different tissues was found to be nonrandom. The coelomic epithelium, the vascular endothelium, and the prepuberal germ cells exhibited predominantly a 47,XYY karyotype. In contrast, Sertoli cells exhibited both karyotypes, and the remaining tissue was predominantly composed of 45,X cells. The contribution of the two cell lines to gonadal development is discussed.