HSP90AA1 variants may contribute to autosomal dominant human male infertility

Study questionDo variants in HSP90AA1 cause human male infertility? Summary answerVariants in HSP90AA1 appear as a possible autosomal dominant cause of human male infertility. What is known alreadyMale infertility is a highly heterogeneous condition, with so far over 300 genes described in this context. HSP90AA1 appears as a promising candidate gene for human male infertility, because the gene is highly conserved between species and knock-out of Hsp90aa1 in mice results in male-specific infertility due to azoospermia without further health implications. Study design, size, durationWe screened >2,300 infertile men for possibly pathogenic variants in HSP90AA1 and created a mouse line harbouring the homozygous missense variant c.605G>A p.(Arg202Lys). Participants/materials, setting, methodsPhenotypes of men with identified variants were determined based on semen analysis and testicular histology. Pathogenicity of detected variants was assessed using AlphaMissense and a mouse model. Male fertility of the mutant mouse line was analysed via plug-matings, histology and immunofluorescence staining (IF). Expression of HSP90AA1 in testicular tissue was assessed by IF. Main results and the role of chanceThe mode of inheritance (MOI) in mice is autosomal recessive but the constraint metrics (oe-score = 0.2, pLI = 1) and in silico prediction suggest that HSP90AA1 is an autosomal dominant gene in humans. We therefore screened for both, heterozygous and biallelic variants in exome sequencing data of infertile men. While we did not detect any biallelic loss-of-function variants, we identified the homozygous missense variant c.605G>A p.(Arg202Lys) in an azoospermic man as a promising variant. This variant is extremely rare and affects a highly conserved amino acid. However, male homozygous mice with this variant are fertile with no differences in litter size and testicular size or histology, making it unlikely that this variant is the cause of the mans azoospermia. We therefore focused on heterozygous possibly pathogenic variants in HSP90AA1 and found a heterozygous frameshift variant in an azoospermic man with hypospermatogenesis as well as four heterozygous missense variants, predicted to affect protein function in azoo- or cryptozoospermic men. Large scale dataN/A Limitations, reasons for cautionOur findings suggest a dominant MOI in humans but currently cannot fully prove this. To further clarify the MOI and ultimately improve clinical validity of HSP90AA1 replication of our findings in independent cohorts of infertile men as well as segregation analyses are required. Wider implications of the findingsWhile most human male infertility genes follow an autosomal recessive MOI, HSP90AA1 might be one of the few autosomal dominant infertility genes in humans. Differences in the MOI between humans and mice are also known from well-established infertility genes such as DMRT1. Study funding/competing interest(s)This work was supported by a German Research Foundation (DFG) fellowship (award WY 215/1-1 to MJW), the DFG-sponsored Clinical Research Unit Male Germ Cells (CRU326, project 329621271 to FT), and Wellcome Trust funding (225237 to DOC). This work was supported by funding for the Wellcome Discovery Research Platform for Hidden Cell Biology (226791).