Abnormal elongation of midpiece, absence of axoneme and outer dense fibers at principal piece level, supernumerary microtubules: a sperm defect of possible genetic origin?

Objective: To characterize a flagellar defect involving 95% of the sperm population from an infertile man.

Design: Case report.

Setting: Interdepartmental Centre for Research and Therapy of Male Infertility, Siena, Italy.

Patient(s): A 42-year-old infertile man with severe asthenozoospermia.

Intervention(s): Family history, physical examination, hormonal analysis, microbial assays, semen analysis, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), tubulin distribution investigated by immunocytochemistry, fluorescence in situ hybridization for chromosomes 18, X, and Y.

Main Outcome Measure(s): Ultrastructural abnormalities of the flagellum detected by methods listed.

Result(s): Ultrastructural analysis revealed, in 95% of sperm cells, the total absence of the axoneme and outer dense fibers at the principal piece level, whereas the midpiece appeared abnormally long. Tubulin localization showed a total disorganization of the axoneme with a network of microtubular structures emerging randomly at any level of the flagellum. Fluorescence in situ hybridization analysis was normal.

Conclusion(s): We report a rare sperm tail defect, characterized by abnormal elongation of the midpiece and absence of the axoneme and the outer dense fibers at the principal piece level in 95% of flagella. This defect occurs in the vast majority of the sperm population from a sterile man, and therefore a genetic origin could be hypothesized.