KATNAL1 polymorphisms confer susceptibility to severe phenotypes of male infertility in a large European cohort

Abstract Study question What is the contribution of the common variation of KATNAL1 to the development of severe spermatogenic failure (SPGF) in a phenotypically well-characterized cohort? Summary answer An allelic combination of KATNAL1 single-nucleotide polymorphisms (SNPs) increases the risk to develop SPGF, likely by altering the expression and splicing pattern of the gene. What is known already Spermatogenesis is a process that requires an exhaustive control of gene expression, and subtle alterations of its molecular regulatory network can lead to male infertility. The aetiology of most SPGF cases remains unknown, and increasing evidence clearly suggests that the idiopathic form of SPGF represents a complex trait, in which genetic susceptibility is conferred by the accumulation of risk alleles in genetically predisposed men. In this regard, previous studies reported that rare genetic mutations and polymorphisms in the KATNAL1 locus lead to male infertility through the disruption of microtubule remodelling and premature germ cell exfoliation. Study design, size, duration We designed a case-control genetic association study including three SNPs (rs2077011, rs7338931, and rs2149971) in the 3' and 5' regulatory regions of KATNAL1, which tagged the common genetic variability in the region. The allele frequencies in the study population, composed of 715 infertile men diagnosed with idiopathic SPGF, were compared to those observed in a control group comprising 1058 fertile men from Spain and Portugal. Participants/materials, setting, methods The SPGF group comprised 210 men with severe oligospermia (SO) and 505 with non-obstructive azoospermia (NOA). The latter were phenotypically characterised according to the histological examination of testis biopsies and its outcome (Sertoli cell-only syndrome, SCO; maturation arrest, MA; hypospermatogenesis, HS; and testicular sperm extraction, TESE). After genotyping, case-control association analyses by logistic regression were conducted. In silico functional characterization of risk variants was also carried out using public multiomic databases and bioinformatic tools. Main results and the role of chance Significant genetic associations with different SPGF patterns and/or TESE outcome were observed even after correction for multiple testing when independent SNP models were tested. However, in all cases, the haplotype model including the three risk alleles (rs2077011*C | rs7338931*T | rs2149971*A) was the most informative. This haplotype was specifically over-represented in the SPGF group (P = 3.45E-02, OR = 2.33), which includes all infertile men, and in the NOA group (P = 8.22E-03, OR = 2.97). In addition, subtype-specific associations were observed with the most severe subgroups, namely MA (P = 2.44E-02, OR = 5.00), SCO (P = 4.03E-03, OR = 5.16), and unsuccessful TESE outcome (P = 2.22E-04, OR = 6.13), which indicates the relevant role of KATNAL1 in spermatogenesis development. We prioritized the most likely causal variant/s based on in silico analyses addressing the possible functional implication of the tagged variants. We observed that an alteration of the KATNAL1 splicing pattern, by favouring the overrepresentation of a short non-functional transcript isoform in the testis, might be the cause behind the observed genetic association. The analysis of the testis transcriptome at the single cell level showed that KATNAL1 transcripts were mostly presented in spermatocytes and early spermatids at puberty, which correlates with its effect of premature exfoliation and loss of the germ cells. Limitations, reasons for caution Although a previous low-powered study reported suggestive associations between KATNAL1 and SPGF, additional genetic association studies in independent populations should be conducted to confirm our findings. Moreover, the statistical power for the overall analysis was appropriate, but the subphenotype analyses were performed with reduced power due to smaller study groups. Wider implications of the findings Our results suggest a relevant role of the common genetic variation of KATNAL1 in the susceptibility to develop the most severe histological phenotypes of NOA (i.e., SCO and MA). Studies like the one presented here may definitively help to develop future non-invasive molecular markers of TESE success. Trial registration number Not Applicable