Detection of chromosomes and estimation of aneuploidy in human spermatozoa using fluorescence in-situ hybridization

The development and application of fluorescence in-situ hybridization(FISH) has opened the way for comprehensive studies on numerical chromosomeabnormalities in human spermatozoa. FISH can be rapidly applied to largenumbers of spermatozoa and thus overcomes the major limitation ofkaryotyping spermatozoa after penetration of zona-free hamster oocytes. Thesimultaneous hybridization of two or more chromosome-specific probes tospermatozoa and subsequent detection of the bound probes using differentfluorescent detection systems enables two or more chromosomes to belocalized simultaneously in the same spermatozoon and provides a techniquefor undertaking reasonable estimates of aneuploidy. The most commonly usedprobes are those which bind to the centromeric region of specificchromosomes. Most studies to date have concentrated on estimatinganeuploidy in spermatozoa from normospermic men, although reports arebeginning to appear on aneuploidy in spermatozoa from subfertile andinfertile men. Multi- probe FISH studies have generally reported disomy(hyperhaploidy) estimates of 0.05-0.2% per chromosome. There is preliminaryevidence that some chromosomes such as X, Y and 21 are predisposed towardshigher rates of non-disjunction during spermatogenesis. There are alsosuggestions of inter-donor variability in aneuploidy frequencies forspecific chromosomes, although this requires confirmation in largerstudies. While FISH is clearly a powerful technique that has manyapplications in reproductive medicine, it must also be realized that itdoes have limitations and the technology itself is still evolving and hasyet to be fully validated on spermatozoa.