FSHB and FSHR genetic variants and testicular function

[madman]

FSHB and FSHR gene variants exert mild modulatory effect on reproductive hormone levels and testis size but not on semen quality: A study of 2,020 men from the general Danish population
Anne Kirstine Bang, Kristian Almstrup, Loa Nordkap, Lærke Priskorn, Jørgen Holm Petersen, Martin Blomberg Jensen, Marianna Krause, Stine Agergaard Holmboe, Dorte Louise Egeberg Palme, Sofia Boeg Winge, Ulla Nordström Joensen, Inge Ahlmann Olesen, Helene Westring Hvidman, Anders Juul, Ewa Rajpert-De Meyts, Niels Jørgensen




Abstract

Background: Spermatogenesis depends on stimulation by follicle-stimulating hormone (FSH) which binds to FSH receptors (FSHR) on testicular Sertoli cells. Three FSH-related single nucleotide polymorphisms (SNPs); FSHB -211G>T (rs10835638), FSHR -29G>A (rs1394205), and FSHR 2039A>G (rs6166) affect FSH action and have been suggested to affect testicular function, but the evidence is uncertain.

Objective: To describe the associations between the three SNPs and testicular function in a large and well-characterized cohort of men from the general population.

Materials and methods: A cross-sectional study of 2,020 Danish men unselected regarding testicular function.
Outcome variables were semen parameters, reproductive hormones, and testis size. Genotyping was done by competitive allele-specific quantitative PCR. Differences in genotype frequencies were tested by Chi-square test and associations between genotypes and outcomes were assessed by multivariate linear regressions.

Results: The SNPs affected serum FSH; carriers of the variant affecting FSH secretion (FSHB - 211G>T) had lower FSH levels while carriers of variants affecting receptor expression (FSHR - 29G>A) and receptor sensitivity (FSHR 2039A>G) had higher FSH levels. Carriers of FSHB - 211G>T had a lower calculated free-Testosterone/LH ratio. Although both FSHB -211G>T and FSHR 2039A>G was associated with smaller testis size, no clear association was detected in relation to any semen parameters, except a lower total number of morphologically normal spermatozoa in the heterozygous carriers of the FSHB -211G>T Discussion and

Conclusion: The studied polymorphisms have only a minor modulating influence on testis size and function in healthy men. We detected subtle effects of the three SNPs on FSH levels, but also effects of FSHB -211G>T on calculated free-Testosterone/LH ratio, compatible with altered Leydig cell function. Thus, the role of these FSH-related polymorphisms is complex and modest in men with normal testicular function, but the possible importance of FSH polymorphisms in men with impaired testicular function should be evaluated in future studies in more detail.





Introduction

Spermatogenesis can be affected by multiple factors including genetic variations modulating the function of the hypothalamus-pituitary-gonadal (HPG) hormone axis1,2 as well as environmental and lifestyle factors3,4.

Single nucleotide polymorphisms (SNPs) in several genes have been associated with male infertility and decreased semen quality1,2. SNPs that affect the follicle-stimulating hormone (FSH) signaling pathway essential for normal spermatogenesis, have gained attention5–9. Particularly, the FSHB -211G>T SNP, located in the promoter region of the FSH beta-subunit, influences the transcription of the FSHB gene and consequently circulating FSH levels10. Minor T-allele carriers of FSHB -211G>T have lower serum levels of FSH and inhibin B and smaller testicular volume10– 15. Furthermore, two FSH receptor (FSHR) SNPs, FSHR -29G>A and FSHR 2039A>G, have been linked to testicular function by affecting the transcription of FSHR and the sensitivity of FSHR, respectively14–19. In some studies, the minor alleles of these three SNPs were found to be more prevalent among infertile men than among men from the general populations and proven fathers11,13,20, the FSHR SNPs in combination with the FSHB -211G>T SNP have been shown to result in a more severe phenotype14. However, other studies found no effect of especially the FSHR variants on male reproduction suggesting that the HPG axis may compensate for the effects of these genetic variants in some men9,21. Here, we address this question by investigating the three most informative SNPs: FSHB -211G>T, FSHR -29G>A, and FSHR 2039A>G on gonadal function, in a very large group of well-characterized young Danish men from the general population.





In conclusion, our study investigated the combined effects of three FSH-related SNPs. The findings of the present study are overall in agreement with previously published studies. Our results do not support a major impact of the FSH-related SNPs on testicular function in men with largely normal testis function. A minor modulating influence of the genotype distribution on the average parameters of the testis function at the population level is possible, though at the individual level the effects of these genotypes on testis function are apparently subtle and likely influenced by other factors in healthy young men.

 

[madman]

Table 1: Basic description of the whole study population (total) and stratified into Subgroup A (without factors potentially affecting testicular function i.e. varicocele, treated cryptorchidism, previous testicular infections, previous minor scrotal injury or operations) and subgroup B with one or more such factors. Values are medians (5-95th percentiles) or percentage

 

[madman]

Table 2: Genotype and allele distribution (percentages) of FSHB - 211G>T, FSHR -29G>A and FSHR 2039A>G of the whole study population (total) and stratified into Subgroup A (without factors potentially affecting testicular function i.e. varicocele, treated cryptorchidism, previous testicular infections, previous minor scrotal injury or operations) and subgroup B with one or more such factors.

 

[madman]

Table 3: Genotype and allele distribution (percentages) of FSHB -211G>T, FSHR -29G>A and FSHR 2039A>G stratified into < or > median levels of FSH, Inhibin B, and testis size, as well as < or > than the WHO criteria for normal levels of total sperm count, in Subgroup A (without factors potentially affecting testicular function i.e. varicocele, treated cryptorchidism, previous testicular infections, previous minor scrotal injury or operations)

 

[madman]

Table 4: Semen parameters, testis size, and hormone levels stratified according to FSHB-211G>T, FSHR-29G>A, and FSHR 2039A>G in men without any known factors that could potentially affect the testicular function (N=1,491, subgroup A). Numbers are median values (min-max). Levels are shown unadjusted and stratified in eight groups according to the combination of the three SNPs described as major allele carriers vs. homozygote and heterozygote carriers (dominant model). Men with azoospermia are not included, but oligozoospermia <0.5 million/ml is shown as 0 million/ml.

 

[madman]

Table 5: Overview of the effect estimates of the three FSH-related SNPs on markers of testicular function in the subgroup without any known factors that could potentially affect the testicular function (n=1,491). Multiple linear regression analyses were adjusted for covariates and the effect of the two other SNPs. P-values were based on models including the transformation of variables giving the best model fit (described in the statistical section). P-values <0.05 are indicated in bold

 

[madman]

Legends to Figure 1: Boxplots of FSH levels (A), Total sperm count (B), and Average testis size (C) for each genotype combination. The boxes represent the 25th-75th percentiles (interquartile range) with the median, and whiskers show the highest and lowest values that are within 1.5 times the interquartile range. Outliers, defined as observations below or above these values, are not depicted in the figure. There were no men in group 26, indicated in grey.

 

[madman]

Legends to Figure 2: Percentage of men with a normal total sperm count (≥39 million) in each of the 27 genotype combinations (FSHB -211G>T, FSHR -29G>A and FSHR 2039A>G) in the subgroup (A) of men without any known factors that could potentially affect the testicular function.