P-538 KATNAL1 polymorphisms confer susceptibility to severe phenotypes of male infertility in a large European cohort

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

P-536 Common variation in the PIN1 locus increases the genetic risk to suffer from Sertoli Cell Only syndrome

Study question

Are the common genetic variants located in the PIN1 region associated with human male infertility due to severe spermatogenic failure (SPGF)?

Summary answer

PIN1 gene polymorphisms may play a relevant role in the development of Sertoli Cell Only syndrome (SCO), the most extreme form of SPGF.

What is known already

PIN1 is a relevant prolyl isomerase in humans, that catalyzes cis/trans isomerization of peptide bonds. It has a central role in cell cycle progression and cancer, and it has been linked to the immune system promoting inflammation and reactive-oxygen species. Pin1 gene is highly expressed in adult mice testes, particularly in spermatogonia and Sertoli cells, and it is required to control the proliferation of spermatogonial stem cells. Additionally, it controls the integrity of the blood-testis barrier, helping to maintain the immune privilege of the testis. Nevertheless, mutations in PIN1 have not yet been described in human male infertility cases.

Study design, size, duration

A genetic association study was performed including samples from 715 men diagnosed with SPGF and classified as suffering from non-obstructive azoospermia (NOA, n = 505) or severe oligospermia (SO, n = 210), and 1,058 matched unaffected male controls from the Iberian Peninsula (Spain and Portugal). Allelic association on SPGF susceptibility were evaluated by testing three PIN1 single nucleotide polymorphisms (SNPs; rs2287839, rs2233678, and rs62105751), which tagged most of the common genetic variation present in this locus.

Participants/materials, setting, methods

Participants signed an informed written consent approved by the ethical committees of each participating center. SO and NOA were clinically defined according to the guidelines of the World Health Organization. Genomic DNA from blood samples was genotyped using TaqMan assays and statistical analyses were carried out by the means of logistic regression models. An in silico functional prioritization of the associated variants and their linked polymorphisms was also performed.

Main results and the role of chance

A subtype-specific genetic association with the subset of NOA patients classified as suffering from SCO was identified for the three analyzed genetic variants under the additive model (rs2287839: P = 1.94E-02, rs2233678: P = 1.94E-02, rs62105751: P = 1.94E-02). The minor alleles showed strong risk effects for this subset (rs2287839: OR = 1.85 [1.17-2.93], rs2233678: OR = 1.62 [1.11-2.36], rs62105751: OR = 1.43 [1.06-1.93]). Dependence analysis showed that all associated variants tagged the same signal. The variants underlying the identified association signal were prioritized based on their functional impact on the PIN1 locus, being rs3810166 the most likely candidate for functionality. The minor allele of such variant (G) is in linkage disequilibrium with the observed rs2287839-G risk allele and it is predicted to affect both gene expression and isoform balance of PIN1. The rs3810166 SNP likely influences the binding affinity of both HDAC2 and NRSF transcription factors, which are involved in cell cycle progression and transcription, respectively. Moreover, the tagged variants rs28802413 and rs10425775 were also predicted to alter the binding of significant transcription factors of the spermatogenic process, such as SIN3A and NANOG.

Limitations, reasons for caution

Although the overall statistical power of the study cohort was appropriate to detect the expected effects, the sample sizes in the subtype analyses were considerably lower, which may influence the obtained results. Further analyses including a larger SCO cohort should be performed to confirm our findings.

Wider implications of the findings

The obtained results shed light into the genetic contribution of common variation to male infertility, which may contribute to design a future panel of genetic markers to predict the testicular sperm extraction outcome, avoiding surgical interventions in NOA cases in which the probability of spermatozoa finding is much reduced.

Trial registration number

Not applicable

O-118 New insight into the genetic contribution of common variants to the development of extreme phenotypes of unexplained male infertility: a multicenter genome-wide association study

Study question

What is the contribution of the common genetic variation to the development of unexplained male infertility due to severe spermatogenic failure (SPGF)?

Summary answer

Genetic polymorphisms of key immune and spermatogenesis loci are involved in the etiology of the most severe SPGF cases, defined by Sertoli cell-only (SCO) phenotype.

What is known already

Male infertility is a rising worldwide concern that affects millions of couples. Non-obstructive azoospermia (NOA) and severe oligospermia (SO) are two extreme manifestations characterized by SPGF. A genetic cause can be established in only around 20% of affected men, with the remaining cases being classified as otherwise unexplained. To date, the genome-wide association study (GWAS) strategy, although already successfully applied in several other complex traits and diseases, was less fruitful in studies that attempted to decipher the genetic component of unexplained SPGF, mainly due to both a lack of well-powered samples in different ancestries and limitations in study design.

Study design, size, duration

We designed a GWAS for unexplained male infertility due to SPGF including a total of 1,274 affected cases and 1,951 fertile controls from the Iberian Peninsula (Spain and Portugal) and Germany. Different biostatistics and bioinformatics approaches were used to evaluate the possible effect of single-nucleotide polymorphisms (SNPs) across the whole genome in the susceptibility to specific subtypes of unexplained SPGF.

Participants/materials, setting, methods

The case cohort comprised 502 SO and 772 NOA patients, who were subdivided according to histological phenotypes (SCO, maturation arrest, and hypospermatogenesis) and the outcome of testicular sperm extraction techniques (TESE) from testis biopsies. Genotyping was performed with the GSA platform (Illumina). After quality-control and genotype imputation, 6,539,982 SNPs remained for the analysis, which was performed by logistic regression models. The datasets went through a meta-analysis by the inverse variance weighted method under fixed effects.

Main results and the role of chance

Genetic associations with SCO at the genome-wide-level of significance were identified in the major histocompatibility (MHC) class II region (rs1136759, OR = 1.80, P = 1.32E-08) and in a regulatory region of chromosome 14 nearby the vaccinia-related kinase 1 (VRK1) gene (rs115054029, OR = 3.14, P = 4.37-08). VRK1 is a relevant proliferative factor for spermatogenesis that causes progressive loss of spermatogonia when disrupted in mouse models. The role of the MHC system in SCO susceptibility was comprehensively evaluated through a validated imputation method that infers classical MHC alleles and polymorphic amino acid positions. A serine at position 13 of the HLA-DRβ1 protein (defined by the risk allele of the lead variant rs1136759) explained most of the SCO association signals within the MHC class II region. This residue is located in the binding pocket of the HLA-DR molecule and interacts directly with the presented antigen. Interestingly, position 13 of HLA-DRβ1 is the most relevant risk amino acid position for a wide spectrum of immune-mediated disorders. The HLA-DRB1*13 haplotype (which includes the serine at position 13 and represents the strongest NOA-associated marker in Asians to date) was the strongest signal amongst the classical MHC alleles in our study cohort (OR = 1.93, P = 9.90E-07).

Limitations, reasons for caution

Although the statistical power for the overall analysis was appropriate, the subphenotype analyses performed had considerably lower counts, which may influence the identification of genetic variants conferring low to moderate risk effects. Independent studies in larger SCO study cohorts should be performed to confirm our findings.

Wider implications of the findings

The molecular mechanisms underlying unexplained SPGF are largely unknown. Our data suggest a relevant role of common genetic variation in the development of SCO, the most extreme histological phenotype of NOA. SCO is characterized by the loss of germ cells and, therefore, implies a considerably higher probability of unsuccessful TESE.

Trial registration number

N/A

A rare polymorphism in the gene for Toll-like receptor 2 is associated with systemic sclerosis phenotype and increases the production of inflammatory mediators

OBJECTIVE

To investigate whether polymorphisms in Toll-like receptor (TLR) genes, previously reported to be associated with immune-mediated diseases, are involved in systemic sclerosis (SSc).

METHODS

We genotyped 14 polymorphisms in the genes for TLRs 2, 4, 7, 8, and 9 in a discovery cohort comprising 452 SSc patients and 537 controls and a replication cohort consisting of 1,170 SSc patients and 925 controls. In addition, we analyzed 15-year followup data on 964 patients to assess the potential association of TLR variants with the development of disease complications. We analyzed the functional impact of the associated polymorphism on monocyte-derived dendritic cells.

RESULTS

In the discovery cohort, we observed that a rare functional polymorphism in TLR2 (Pro631His) was associated with antitopoisomerase (antitopo) positivity (odds ratio 2.24 [95% confidence interval 1.24-4.04], P=0.003). This observation was validated in the replication cohort (odds ratio 2.73 [95% confidence interval 1.85-4.04], P=0.0001). In addition, in the replication cohort the TLR2 variant was associated with the diffuse subtype of the disease (P=0.02) and with the development of pulmonary arterial hypertension (PAH) (Cox proportional hazards ratio 5.61 [95% confidence interval 1.53-20.58], P=0.003 by log rank test). Functional analysis revealed that monocyte-derived dendritic cells carrying the Pro63His variant produced increased levels of inflammatory mediators (tumor necrosis factor α and interleukin-6) upon TLR-2-mediated stimulation (both P<0.0001).

CONCLUSION

Among patients with SSc, the rare TLR2 Pro631His variant is robustly associated with antitopoisomerase positivity, the diffuse form of the disease, and the development of PAH. In addition, this variant influences TLR-2-mediated cell responses. Further research is needed to elucidate the precise role of TLR-2 in the pathogenesis of SSc.