Three cases of genetic defects affecting sperm tail: a FISH study

Submicroscopic alterations in the cytoskeletal structure of sperm flagellum are associated with severely reduced or completely absent motility in subfertile or infertile men. Sometimes these alterations can be related to well known genotypic defects when the same anomaly affects the whole sperm population. Transmission electron microscopy (TEM) is the only tool able to specifically characterize the morphological features of genetic sperm defects. In this study, the frequencies of aneuploid and diploid spermatozoa were identified in three patients showing specific flagellar anomalies, each of them affecting the whole sperm population: dysplasia of the fibrous sheath, primary ciliary dyskinesia and absence of fibrous sheath. All these defects were highlighted by TEM. Fluorescence in situ hybridization (FISH) analysis was performed on decondensed sperm nuclei for chromosomes 18, X and Y, highlighting higher diploidies and sex chromosome disomies in cases of dysplasia of the fibrous sheath and primary ciliary dyskinesia, in agreement with other reports. We have also described FISH results in spermatozoa with absence of fibrous sheath. In this case, the only one reported due to the rarity of this defect, the aneuploidies and diploidies were within normal range. These data contribute to the growing evidence that genetic sperm defects of sperm flagella are generally correlated with meiotic segregation derangement. For this reason, genetic counseling is advisable, although all the genes involved and the possible mechanisms of these mutations have not yet been fully characterized.