Fertilizing potential of acrosome-defective sperm following microsurgical injection into eggs.

Ejaculates from three infertile men were examined ultrastructurally and found to include a high number of amorphous acrosomeless spermatozoa. Two of the patient's spermatozoa exhibited the typical characteristics of round-head syndrome--spherical-shaped heads completely absent of acrosome and postacrosomal sheath. The semen of the third patient was found to contain a mixture of round-headed and irregularly shaped acrosomeless sperm and a small percentage of normal acrosome-intact sperm. Previous studies have shown that acrosomeless sperm do not have the ability to bind or penetrate zona-free hamster eggs (Weissenberg et al., Syms et al.). In an attempt to determine if such amorphous sperm are capable of decondensation and pronuclear formation, sperm of all three men were microsurgically injected into zona-intact hamster eggs. All of the sperm injected were found to be capable of decondensation or pronuclear formation, suggesting that if the inability to penetrate an egg is bypassed, the sperm of these infertile men are capable of participating in the early events of fertilization.