Genotype-specific differences in infertile men due to loss-of-function variants inM1APorZZSgenes

Male infertility and meiotic arrest have been linked toM1AP, the gene encoding meiosis I associated protein. In mice, M1AP interacts with the ZZS proteins SHOC1, TEX11, and SPO16, which promote DNA class I crossover formation during meiosis. To determine whether M1AP and ZZS proteins are involved in human male infertility by disrupting class I crossover formation, we screened for biallelic or hemizygous loss-of-function (LoF) variants in the encoding human genes to select men with a presumed protein deficiency; we compiled N=10 men forM1AP, N=4 forSHOC1, N=9 forTEX11,and the first homozygous LoF variant inSPO16in an infertile man. After in-depth characterisation of the testicular phenotype of these men, we identified gene-specific meiotic impairments: men with SHOC1, TEX11, or SPO16 deficiency shared an early meiotic arrest lacking haploid germ cells. All men with LoF variants inM1APexhibited a predominant metaphase I arrest with rare haploid round spermatids, and six men even produced sporadic elongated spermatids. These differences were explained by different recombination failures: abrogated SHOC1, TEX11, or SPO16 led to incorrect synapsis of homologous chromosomes and unrepaired DNA double-strand breaks (DSB). On the contrary, abolished M1AP did not affect synapsis and DSB repair but led to a reduced number of class I crossover events. Notably, medically assisted reproduction resulted in the birth of a healthy child, offering the possibility of fatherhood to men with LoF variants inM1AP. Our study establishes M1AP as an important, but not essential, functional enhancer in the network of ZZS-mediated meiotic recombination.