Chromosome analysis of human spermatozoa with morphologically abnormal heads by injection into mouse oocytes

Aim:  The risk of chromosome aberrations in human spermatozoa with an abnormal head shape was examined using intracytoplasmic sperm injection into mouse oocytes. Methods:  Human spermatozoa with small, large, pointed or elongated head shape from a fertile donor were injected into mouse oocytes, and the hybrid oocytes were cytogenetically analyzed at the first cleavage metaphase. Results:  The oocyte activation rate was significantly lower in hybrid oocytes injected with pointed (90.2%) or elongated spermatozoa (94.1%) than with normal spermatozoa (99.0%). However, the frequency of intracytoplasmic sperm injection oocytes at the first cleavage metaphase did not differ among the sperm groups (71.8-77.2%). No difference in the incidences of aneuploidy (1.8, 2.6 and 1.4%), diploidy (0, 0 and 0%) and structural chromosome aberrations (6.3, 10.4 and 8.6%) was observed between small or pointed spermatozoa and normal spermatozoa. Only a small population of large spermatozoa (3.7%) was diploidy. Elongated spermatozoa showed significantly frequent structural chromosome aberrations (33.3%) as compared with normal spermatozoa. Conclusion:  The results reveal some interesting details of the mechanism of sperm nuclear condensation: small sperm size is attributed to the problem of nuclear condensation, not a decrease in chromosomes. Diploidy prevents sperm nucleus from condensing, resulting in a large sperm head. Elongation of sperm nucleus causes DNA lesions leading to structural chromosome aberrations. (Reprod Med Biol 2004; 3: 147-152).