Intérêt de la cytogénétique des gamètes humains : résultats et perspectives

Aneuploidy in human spermatozoa

We reviewed the frequency and distribution of disomy in spermatozoa obtained by multicolor-FISH analysis on decondensed sperm nuclei in (a) healthy men, (b) fathers of aneuploid offspring of paternal origin and (c) individuals with Klinefelter syndrome and XYY males. In series of healthy men, disomy per autosome is approximately 0.1% but may range from 0.03 (chromosome 8) to 0.47 (chromosome 22). The great majority of authors find that chromosome 21 (0.18%) and the sex chromosomes (0.27%) have significantly elevated frequencies of disomy although these findings are not universal. The total disomy in FISH studies is 2.26% and the estimated aneuploidy (2× disomy) is 4.5%, more than double that seen in sperm karyotypes (1.8%). Increased disomy levels of low orders of magnitude have been reported in spermatozoa of some normal men (stable variants) and in men who have fathered children with Down, Turner and Klinefelter syndromes. These findings suggest that men with a moderately elevated aneuploidy rate may be at a higher risk of fathering paternally derived aneuploid pregnancies. Among lifestyle factors, smoking, alcohol and caffeine have been studied extensively but the compounding effects of the 3 are difficult to separate because they are common lifestyle behaviors. Increases in sex chromosome abnormalities, some autosomal disomies, and in the number of diploid spermatozoa are general features in 47,XXY and 47,XYY males. Aneuploidy of the sex chromosomes is more frequent than aneuploidy of any of the autosomes not only in normal control individuals, but also in patients with sex chromosome abnormalities and fathers of paternally derived Klinefelter, Turner and Down syndromes.

[Half a century of human and medical cytogenetics]

In 1956, the number of chromosomes in humans is set at 46; in 1959, the link between a disability (mongolism) and a chromosomal anomaly (the Down syndrome) is established: human and medical cytogenetics were born. Since then, progress has been remarkable: the techniques of chromosomal and molecular cytogenetics can reach a resolution of the size of a single gene with a pangenomic scope. Practical applications are constantly expanded. The clinical impact is significant, from the genetic counselling in constitutional to the targeted therapies. Fifty years later, cytogenetics can be defined as the science which aims to detect chromosomal abnormalities, whether constitutional or acquired, using chromosomal or molecular techniques aiming to study the arrangement of genes in chromosomes, to quantify the number of gene copy and to look for the presence of gene fusion.