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

Altered gene expression signature of early stages of the germ line supports the pre-meiotic origin of human spermatogenic failure

The molecular basis of spermatogenic failure (SpF) is still largely unknown. Accumulating evidence suggests that a series of specific events such as meiosis, are determined at the early stage of spermatogenesis. This study aims to assess the expression profile of pre-meiotic genes of infertile testicular biopsies that might help to define the molecular phenotype associated with human deficiency of sperm production. An accurate quantification of testicular mRNA levels of genes expressed in spermatogonia was carried out by RT-qPCR in individuals showing SpF owing to germ cell maturation defects, Sertoli cell-only syndrome or conserved spermatogenesis. In addition, the gene expression profile of SpF was compared with that of testicular tumour, which is considered to be a severe developmental disease of germ cell differentiation. Protein expression from selected genes was evaluated by immunohistochemistry. Our results indicate that SpF is accompanied by differences in expression of certain genes associated with spermatogonia in the absence of any apparent morphological and/or numerical change in this specific cell type. In SpF testicular samples, we observed down-regulation of genes involved in cell cycle (CCNE1 and POLD1), transcription and post-transcription regulation (DAZL, RBM15 and DICER1), protein degradation (FBXO32 and TM9SF2) and homologous recombination in meiosis (MRE11A and RAD50) which suggests that the expression of these genes is critical for a proper germ cell development. Interestingly, a decrease in the CCNE1, DAZL, RBM15 and STRA8 cellular transcript levels was also observed, suggesting that the gene expression capacity of spermatogonia is altered in SpF contributing to an unsuccessful sperm production. Altogether, these data point to the spermatogenic derangement being already determined at, or arising in, the initial stages of the germ line.

N-terminal CFTR missense variants severely affect the behavior of the CFTR chloride channel

Over 1,500 cystic fibrosis transmembrane conductance regulator (CFTR) gene sequence variations have been identified in patients with cystic fibrosis (CF) and related disorders involving an impaired function of the CFTR chloride channel. However, detailed structure-function analyses have only been established for a few of them. This study aimed evaluating the impact of eight N-terminus CFTR natural missense changes on channel behavior. By site-directed mutagenesis, we generated four CFTR variants in the N-terminal cytoplasmic tail (p.P5L, p.S50P, p.E60K, and p.R75Q) and four in the first transmembrane segment of membrane-spanning domain 1 (p.G85E/V, p.Y89C, and p.E92K). Immunoblot analysis revealed that p.S50P, p.E60K, p.G85E/V, and p.E92K produced only core-glycosylated proteins. Immunofluorescence and whole cell patch-clamp confirmed intracellular retention, thus reflecting a defect of CFTR folding and/or trafficking. In contrast, both p.R75Q and p.Y89C had a glycosylation pattern and a subcellular distribution comparable to the wild-type CFTR, while the percentage of mature p.P5L was considerably reduced, suggesting a major biogenesis flaw on this channel. Nevertheless, whole-cell chloride currents were recorded for all three variants. Single-channel patch-clamp analyses revealed that the channel activity of p.R75Q appeared similar to that of the wild-type CFTR, while both p.P5L and p.Y89C channels displayed abnormal gating. Overall, our results predict a major impact of the CFTR missense variants analyzed, except p.R75Q, on the CF phenotype and highlight the importance of the CFTR N-terminus on channel physiology.

Molecular evaluation of CFTR sequence variants in male infertility of testicular origin

Although the involvement of the CFTR gene has been well established in congenital agenesia of vas deferens, its role in non-obstructive (NOb) infertility is still a matter of debate. In order to definitively define the involvement of the CFTR gene in spermatogenic impairment and a potential synergistic contribution to known genetic and clinical factors, genetic variants in the entire coding sequence and the immediately flanking regions of the CFTR gene, along with a thorough clinical evaluation, were analysed in 83 NOb infertile patients and 87 clinically well-defined fertile individuals as controls. The results of our study showed no statistical difference between CFTR carrier frequency in the infertile and fertile population. Specifically, the IVS8-6(5T) allele carrier frequency was similar in NOb infertile patients when compared with fertile men, but it is noteworthy that, when fertile men were classified into having optimal and suboptimal fertility, no 5T allele was found among the 35 men with optimal fertility parameters. In conclusion, extensive CFTR analysis in infertile individuals and fertile population as adequate control definitively excludes the involvement of the CFTR gene variants in sperm production and stresses the importance of carefully identifying those individuals with obstructive defects, in whom CFTR screening will be beneficial.

ATB(0)/SLC1A5 gene. Fine localisation and exclusion of association with the intestinal phenotype of cystic fibrosis

The Na+-dependent amino acid transporter named ATB(0) was previously found to be located in 19q13.3 by fluorescence in situ hybridisation. Genetic heterogeneity in the 19q13.2-13.4 region, syntenic to the Cystic Fibrosis Modulator Locus 1 (CFM1) in mouse, seemed to be associated to the intestinal phenotypic variation of cystic fibrosis (CF). We performed fine chromosomal mapping of ATB(0) on radiation hybrid (RH) panels G3 and TNG. Based on the most accurate location results from TNG-RH panel, mapping analysis evidenced that ATB(0) is localised between STS SHGC-13875 (D19S995) and STS SHGC-6138 in 19q13.3, that corresponds with the immediately telomeric/distal segment of the strongest linkage region within the human CFM1 (hCFM1) syntenic region. Regarding to the genomic structure and exon organisation, our results show that the ATB(0) gene is organised into eight exons. The knowledge of the genomic structure allowed us to perform an exhaustive mutational analysis of the gene. Evaluation of the possible implication of ATB(0) in the intestinal phenotype of CF was performed on the basis of the functional characteristics of the encoded protein, its apparent relevance to meconium ileus (MI) and position in relation to the hCFM1 syntenic region. We have analysed this gene in samples from CF patients with and without MI. Several sequence variations in the ATB(0) gene were identified, although none of them seemed to be related to the intestinal phenotype of CF. Even though no particular allele or haplotype in ATB(0) appears to be associated to CF-MI disease, new SNPs identified should be useful in segregation and linkage disequilibrium analyses in families affected by other disorders caused by the impairment of neutral amino acid transport.

Adenosine triphosphate-binding cassette superfamily transporter gene expression in severe male infertility

Cystic fibrosis transmembrane regulator (CFTR), multidrug-resistant (MDR)1, and multidrug resistance-associated (MRP) proteins belong to the ATP-binding cassette (ABC) transporter superfamily. A compensatory regulation of MDR1 and CFTR gene expression has been observed in CFTR knockout rodent intestine and in an epithelial cell line of human colon, whereas a high homology and similar anion binding site are shared by MRP and CFTR proteins. To provide better insight into the relationship among the expression behavior in vivo of the three genes in human testis, analysis of MDR1 and MRP gene expression in testicular biopsies was performed and related to the presence of CFTR gene mutations in congenital absence of the vas deferens (CAVD: n = 20) and non-CAVD (n = 30) infertile patients with azoospermia or severe oligozoospermia. A CFTR mutation analysis performed in both groups of patients supported the involvement of CFTR gene mutations in CAVD phenotype (85%) and in defective spermatogenesis (19%). Quantitative reverse transcription-polymerase chain reaction analysis of testicular tissue showed a CFTR-independent MDR1 and MRP gene expression in human testis, suggesting that the mechanisms underlying CFTR gene regulation in testis are different from those in intestine. These findings should contribute to the understanding of patterns of in vivo expression of CFTR, MDR1, and MRP genes in CFTR-related infertility.

Heterogeneity for mutations in the CFTR gene and clinical correlations in patients with congenital absence of the vas deferens

Congenital absence of the vas deferens (CAVD) is a heterogeneous disorder, largely due to mutations in the cystic fibrosis (CFTR) gene. Patients with unilateral absence of the vas deferens (CUAVD) and patients with CAVD in association with renal agenesis appear to have a different aetiology to those with isolated CAVD. We have studied 134 Spanish CAVD patients [110 congenital bilateral absence of the vas deferens (CBAVD) and 24 CUAVD], 16 of whom (six CBAVD, 10 CUAVD) had additional renal anomalies. Forty-two different CFTR mutations were identified, seven of them being novel. Some 45% of the CFTR mutations were specific to CAVD, and were not found in patients with cystic fibrosis or in the general Spanish population. CFTR mutations were detected in 85% of CBAVD patients and in 38% of those with CUAVD. Among those patients with renal anomalies, 31% carried one CFTR mutation. Anomalies in seminal vesicles and ejaculatory ducts were common in patients with CAVD. The prevalence of cryptorchidism and inguinal hernia appeared to be increased in CAVD patients, as well as nasal pathology and frequent respiratory infections. This study confirms the molecular heterogeneity of CFTR mutations in CAVD, and emphasizes the importance of an extensive CFTR analysis in these patients. In contrast with previous studies, this report suggests that CFTR might have a role in urogenital anomalies.

Testicular CFTR splice variants in patients with congenital absence of the vas deferens

The involvement of the five thymidine (5T) variant in intron 8 of the cystic fibrosis membrane regulator (CFTR) gene in congenital bilateral absence of the vas deferens (CBAVD) phenotype has been extensively demonstrated. This variant leads to alternative splicing of the CFTR gene which results in a wild-type transcript and one without exon 9. Little is known about expression of the CFTR gene in the testis. We analysed the level of the aberrantly spliced transcripts in testicular biopsies and correlated it with disease expression. Quantitative RT-PCR analysis in testicular biopsies from control and CBAVD patients showed a correlation between the length of the IVS8-6(T) n tract and the level of alternatively spliced transcripts. Results from histological analysis also suggest an involvement of the alternative transcript in the spermatogenic status of patients, leading to a decreased number of mature sperm forms in the tubule.

High heterogeneity for cystic fibrosis in Spanish families: 75 mutations account for 90% of chromosomes

We have analyzed 640 Spanish cystic fibrosis (CF) families for mutations in the CFTR gene by direct mutation analysis, microsatellite haplotypes, denaturing gradient gel electrophoresis, single-strand conformation analysis and direct sequencing. Seventy-five mutations account for 90.2% of CF chromosomes. Among these we have detected seven novel CFTR mutations, including four missense (G85V, T582R, R851L and F1074L), two nonsense (E692X and Q1281X) and one splice site mutation (711+3A-->T). Three variants, two in intronic regions (406-112A/T and 3850-129T/C) and one in the coding region (741C/T) were also identified. Mutations G85V, T582R, R851L, E692X and Q1281X are severe, with lung and pancreatic involvement; 711+3A-->T could be responsible for a pancreatic sufficiency/insufficiency variable phenotype; and F1074L was associated with a mild phenotype. These data demonstrate the highest molecular heterogeneity reported so far in CF, indicating that a wide mutation screening is necessary to characterize 90% of the Spanish CF alleles.

Androgen binding protein is tissue-specifically expressed and biologically active in transgenic mice

In view of the inconclusive data concerning the role of androgen-binding protein (ABP) in male reproductive physiology, we thought it would be pertinent to make several transgenic mouse lines overexpressing the rat ABP gene to unravel its role in Sertoli cell and epididymal homeostasis. Heterozygote transgenic mouse lines carrying the 5.5 kb ABP rat genomic DNA were produced by pronuclear microinjection. Northern blot analysis showed overexpression of rat ABP (rABP) mRNA in the testis of transgenic mice compared to rat testis control. rABP was appropriately expressed in Sertoli cells as demonstrated by in situ hybridization analysis. Sertoli cell number is increased in the seminiferous tubules of mice overexpressing rABP compared to non-transgenic littermates and scattered Sertoli cells present vacuolated-like cytoplasms, PAS and osmium negative. Compared to the wild type, the transgenic mice exhibited reduced fertility and focal damage in seminiferous epithelium characterized by morphological features compatible with programmed cell death.