Loss-of-function mutations in IQCN cause male infertility in humans and mice owing to total fertilization failure.

Fertilization failure is a significant manifestation of unexplained male infertility. Previous work suggested a genetic origin. In this study, we report on a man with unexplained infertility from a large consanguineous marriage family. Whole-exome sequencing and Sanger sequencing identified a homozygous frameshift variation of the IQ motif containing N (IQCN; Genbank: NM_001145304.1; c.1061_1062delAT; p. Y354Sfs*13) in the proband and one of his two brothers, who also remained infertile. Analyses of spermatozoa by quantitative RT-PCR indicated that the level of IQCN mRNA was significantly reduced compared to fertile men and the protein could not be detected by western blotting and immunofluorescent staining in the proband. Immunofluorescent staining of spermatozoa from fertile men showed that IQCN was located in the acrosomal region and translocated to the equatorial segment after acrosome reaction. The proband spermatozoa had abnormal morphology and function. Finally, the proband couple underwent IVF with donor sperm and a healthy baby was born. Furthermore, we developed an Iqcn-KO mouse model using the CRISPR/Cas9 technique. Sperm quality, except for sperm motility, and the fertilityof male Iqcn-/- mice were consistent with those of the proband. In conclusion, the findings in humans and mice demonstrate that the homozygous frameshift variant of IQCN causes male infertility owing to autosomal-recessive fertilization failure.