Detection of sex chromosomal aneuploidies X-X, Y-Y, and X-Y in human sperm using two-chromosome fluorescence in situ hybridization.

Sex chromosome aneuploidy is the most common numerical chromosomal abnormality in humans at birth and a substantial portion of these abnormalities involve paternal chromosomes. An efficient method is presented for using air-dried smears of human semen to detect the number of X and Y chromosomes in sperm chromatin using two-chromosome fluorescence in situ hybridization. Air-dried semen smears were pre-treated with dithiothreitol and 3,4-diiodosalicylate salt to decondense the sperm chromatin and then were hybridized with repetitive sequence DNA probes that had been generated by PCR and differentially labeled. Hybridizations with X and Y specific probes showed the expected ratio of 50%X:50%Y bearing sperm. Sperm carrying extra fluorescence domains representing disomy for the X or Y chromosomes occurred at frequencies of approximately 4 per 10,000 sperm each. Cells carrying both X and Y fluorescence domains occurred at a frequency of approximately 6/10,000. Thus, the overall frequency of sperm that carried an extra sex chromosome was 1.4/1,000. The frequencies of sperm carrying sex chromosome aneuploidies determined by hybridization did not differ statistically from those reported from the same laboratory using the human-sperm/hamster-egg cytogenetic technique. Multi-chromosome fluorescence in situ hybridization to sperm is a promising method for assessing sex-ratio alterations in human semen and for determining the fraction of sperm carrying sex or other chromosome aneuploidies which may be transmissible to offspring.