Comparison of the frequency of defective sperm-zona pellucida (ZP) binding and the ZP-induced acrosome reaction between subfertile men with normal and abnormal semen

BACKGROUND: The aim of this study was to compare the frequency of defective sperm-zona pellucida (ZP) binding (DSZPB) and defective ZP-induced acrosome reaction (DZPIAR) in subfertile men (i.e. male partners of infertile couples) with normal and abnormal semen analyses. METHODS: A total of 1030 subfertile men with normal semen analysis (n = 255), oligozoospermia (count <20 x 10(6)/ml, n = 136), severe teratozoospermia (strict normal morphology <5%, n = 294) and mild-moderate teratozoospermia (morphology 6-14%, n = 345) were studied. Unfertilized oocytes from clinical in vitro fertilization/intracytoplasmic sperm injection were used for sperm-ZP interaction tests. After 2 h incubation of motile sperm with four oocytes, sperm tightly bound to the ZP, and the AR of ZP-bound sperm (ZPIAR) were assessed. An average of <40 sperm bound/ZP and <16% ZPIAR were used for diagnosis of DSZPB or DZPIAR. RESULTS: For the groups of men with normal semen or mild-moderate teratozoospermia, severe teratozoospermia and oligozoospermia, the frequencies of DSZPB were: 13, 21, 29 and 28%, respectively, and in those normal SZPB, DZPIAR were 27, 36, 56 and 68%, respectively. Overall DSZPB and ZPIAR were 36, 49, 68 and 77% for the four groups, respectively. The highest frequencies of defective sperm-ZP interaction were in the oligozoospermia and severe teratozoospermia groups. In the normal and teratozoospermia groups, subjects with a relatively low sperm concentration (20-60 x 10(6)/ml) had a significantly higher frequency of DZPIAR. CONCLUSION: Defective sperm-ZP interaction is a major mechanism of male infertility. DZPIAR is more frequent than DSZPB in subfertile men with either normal or abnormal semen, suggesting that sequential sperm-ZP interaction tests are essential to detect these sperm defects.