Chromosome studies in human sperm nuclei using fluorescence in-situ hybridization (FISH)

The use of chromosome specific DNA probes labelled with fluorochromesand especially the combination of several probes has been usedto indirectly study the chromosome constitution in condensedsperm nuclei by fluorescence in-situ hybridization (FISH), andhas allowed to include this test in the protocol of study ofinfertile males. Still, if the test is to be valid, severalstrict conditions must be met, and some specific characteristicshave to be taken into account. This becomes evident when comparingearlier results with more recent ones. The basic technical factorsto be taken into account are the methods of chromatin decondensation,the number of spermatozoa and of individuals to study, the useof internal controls, the scoring criteria, the specificityof the probes and the possible existence of polymorphisms thatmay interfere with the detection of flourescent signals. Inthe last 7 or 8 years, a large number of papers has been published,describing the incidence of aneuploidies in controls, in individualsin whom a tendency to non-disjunction was suspected and in infertilemales. Studies in controls have shown a considerable intra-and inter-individual variability in the frequency of aneuploidies,the tendency of some chromosomes to undergo non-disjunction(chromosome 21 and the sex chromosomes) and the importance of-satellite polymorphisms when using centromere probes. In thecontrol population, the frequency of aneuploidy per haploidset has been estimated at 6%. The incidence of aneuploidiesin sperm nuclei for some of the chromosomes more frequentlyinvolved in trisomies is considerably higher than the incidenceof these trisomies established through epidemiological datausing the global incidence of chromosome abnormalities duringthe peri-implantation stage. In infertile males and in maleswith sex-chromosome abnormalities (usually with very low numbersof spermatozoa) the results show an increased incidence of sexchromosome aneuploidies and diploid (multi-aneuploid?) spermnuclei. The results could be related to the higher incidenceof chromosome abnormalities (especially sex-chromosome aneuploidies)observed in children conceived by intracytoplasmic sperm injection(ICSI).