Meiotic anomalies. Implications in male sterility

Meiotic anomalies are synaptic chromosome abnormalities, limited to the germ cells, that cannot be detected through the study of the karyotype. Meiotic anomalies can be studied by classical meiotic preparations from testicular tissue, and from a clinical point of view, is still the best approach. Sperm chromosome FISH (fluorescent in situ hybridization) studies also provide indirect evidence of their presence. Meiotic anomalies can produce achiasmate small univalents, partially achiasmate medium-sized or large bivalents, or affect all bivalents in the cell. The frequency is variable, interindividually and intraindividually. The baseline incidence of synaptic anomalies is 6-8%, which may be increased to 17.6% in males with a severe oligozoospermia, and to 27% in normozoospermic males with one or more previous IVF (in vitro fertilization) failures. The clinical consequences are the production of chromosomally abnormal spermatozoa, that will produce a higher number of chromosomally abnormal embryos. The indications for a meiotic study in testicular biopsy and the clinical interpretation of the results obtained are provided. © 2008 Sociedad Española de Andrología.