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

The risk of chromosome aberrations in human spermatozoa with an abnormal head shape was examined using intracytoplasmic sperm injection into mouse oocytes. 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. 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. 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; : 147-152).