CAG repeat length variation in the Androgen Receptor gene is not associated with spermatogenic failure

CAGn Polymorphic Locus of Androgen Receptor (AR) Gene in Russian Infertile and Fertile Men

The androgen receptor (AR) is critical for mediating the effects of androgens. The polymorphic CAGn locus in exon 1 of the AR gene is associated with several diseases, including spinal and bulbar muscular atrophy (SBMA), prostate cancer, and male infertility. This study evaluated the CAGn locus in 9000 infertile Russian men and 286 fertile men (control group). The CAGn locus was analyzed using the amplified fragment length polymorphism method. In the infertile cohort, the number of CAG repeats ranged from 6 to 46, with a unimodal distribution. The number of CAG repeats in infertile and fertile men was 22.15 ± 0.93 and 22.02 ± 1.36, respectively. In infertile men, variants with 16 to 29 repeats were present in 97% of the alleles. A complete mutation (≥42 CAG repeats) was found in three patients, while three others had 39-41 repeats. The incidence of SBMA was 1:3000 infertile men. Significant differences (p < 0.05) were observed between infertile and fertile men in alleles with 21, 24 and 25 repeats. This study revealed certain differences in the CAGn polymorphic locus of the AR gene in Russian infertile and fertile men and determined the frequency of SBMA in infertile patients.

Genetic Landscape of Nonobstructive Azoospermia and New Perspectives for the Clinic

Nonobstructive azoospermia (NOA) represents the most severe expression of male infertility, involving around 1% of the male population and 10% of infertile men. This condition is characterised by the inability of the testis to produce sperm cells, and it is considered to have an important genetic component. During the last two decades, different genetic anomalies, including microdeletions of the Y chromosome, karyotype defects, and missense mutations in genes involved in the reproductive function, have been described as the primary cause of NOA in many infertile men. However, these alterations only explain around 25% of azoospermic cases, with the remaining patients showing an idiopathic origin. Recent studies clearly suggest that the so-called idiopathic NOA has a complex aetiology with a polygenic inheritance, which may alter the spermatogenic process. Although we are far from a complete understanding of the molecular mechanisms underlying NOA, the use of the new technologies for genetic analysis has enabled a considerable increase in knowledge during the last years. In this review, we will provide a comprehensive and updated overview of the genetic basis of NOA, with a special focus on the possible application of the recent insights in clinical practice.

Impact of CAG repeat length in the androgen receptor gene on male infertility - a meta-analysis

CAG repeats are polymorphic nucleotide repeats present in the androgen receptor gene. Many studies have estimated the association between CAG repeat length and male infertility, but the conclusions are controversial. Previous meta-analyses have come to different conclusions; however, new studies have been published. An updated meta-analysis was conducted. PubMed, CBM, CNKI and Web of Science databases were systematically searched for studies published from 1 January 2000 to 1 October 2015. Case-control studies on the association between CAG repeat length and male infertility using appropriate methodology were included. Forty studies were selected, including 3858 cases and 3161 controls. Results showed statistically significantly longer CAG repeat length among cases compared with controls (SMD = 0.14; 95% CI, 0.02-0.26). Shorter repeat length was associated with a lower risk of male infertility compared with a longer repeat length in the overall analysis (OR = 0.79, 95% CI: 0.66-0.95). Moreover, CAG repeat length was associated with male infertility in Caucasian populations, but not Asian or Egyptian populations. Subgroup analysis revealed no significant difference in German populations, but CAG repeat length was associated with male infertility in China and the USA. There were no significant differences between cases and controls in azoospermia and severe oligozoospermia.

Genetic Association Between Androgen Receptor Gene CAG Repeat Length Polymorphism and Male Infertility: A Meta-Analysis

The association between polymorphism of androgen receptor gene CAG (AR-CAG) and male infertility in several studies was controversial. Based on studies on association between AR-CAG repeat length and male infertility in recent years, an updated meta-analysis is needed. We aimed to evaluate the association between AR-CAG repeat length and male infertility in advantage of the data in all published reports.We searched for reports published before August 2015 using PubMed, CNKI, VIP, and WanFang. Data on sample size, mean, and standard deviation (SD) of AR-CAG repeat length were extracted independently by 3 investigators.Forty-four reports were selected based on criteria. The overall infertile patients and azoospermic patients were found to have longer AR-CAG repeat length (standard mean difference (SMD) = 0.19, 95% confidence interval (CI): 0.10-0.28, P < 0.01; SMD = 0.36, 95% CI: 0.10-0.61, P < 0.01). AR-CAG repeat length was longer in infertile men in Asian, Caucasian, and mixed races (SMD = 0.25, 95% CI: 0.08-0.43, P <0.01; SMD = 0.13, 95% CI: 0.02-0.25, P <0.05; SMD = 0.39, 95% CI: 0.15-0.63, P <0.01). The overall study shows that increased AR-CAG repeat length was associated with male infertility. The subgroup study on races shows that increased AR-CAG repeat length was associated with male infertility in Asian, Caucasian, and mixed races. Increased AR-CAG repeat length was also associated with azoospermia.This meta-analysis supports that increased androgen receptor CAG length is capable of causing male infertility susceptibility.

Male Reproductive Disorders and Fertility Trends: Influences of Environment and Genetic Susceptibility

It is predicted that Japan and European Union will soon experience appreciable decreases in their populations due to persistently low total fertility rates (TFR) below replacement level (2.1 child per woman). In the United States, where TFR has also declined, there are ethnic differences. Caucasians have rates below replacement, while TFRs among African-Americans and Hispanics are higher. We review possible links between TFR and trends in a range of male reproductive problems, including testicular cancer, disorders of sex development, cryptorchidism, hypospadias, low testosterone levels, poor semen quality, childlessness, changed sex ratio, and increasing demand for assisted reproductive techniques. We present evidence that several adult male reproductive problems arise in utero and are signs of testicular dysgenesis syndrome (TDS). Although TDS might result from genetic mutations, recent evidence suggests that it most often is related to environmental exposures of the fetal testis. However, environmental factors can also affect the adult endocrine system. Based on our review of genetic and environmental factors, we conclude that environmental exposures arising from modern lifestyle, rather than genetics, are the most important factors in the observed trends. These environmental factors might act either directly or via epigenetic mechanisms. In the latter case, the effects of exposures might have an impact for several generations post-exposure. In conclusion, there is an urgent need to prioritize research in reproductive physiology and pathophysiology, particularly in highly industrialized countries facing decreasing populations. We highlight a number of topics that need attention by researchers in human physiology, pathophysiology, environmental health sciences, and demography.

Have androgen receptor gene CAG and GGC repeat polymorphisms an effect on sperm motility in infertile men?

Androgens and a normal androgen receptor (AR) are required for normal spermatogenesis. We investigated polyglutamine (CAG) and a polyglycine (GGC) tract in Italian men with defective spermatogenesis. We studied a group of 40 infertile men with spermatogenesis failure without Y-chromosome microdeletions compared with 60 normozoospermic ones. The distributions of both polymorphisms, within the normal range of Caucasian populations, were similar among infertile men and controls. Nonetheless, we observed that the frequency comparison of each CAG allele showed a statistical difference in the allele CAG 22; GGC 17 was the more predominant allele in infertile men than in controls. Moreover, to investigate the hypothesis that semen characteristics are perturbed by androgen receptor allele variants, we tried to detect a link between triplets and sperm motility in all subjects (cases plus controls). Subjects were subdivided into three groups, based on calculated allele frequencies. A significantly decreased motility, related to a longer CAG and GGC tracts, and marked differences between the groups exist for both polymorphisms. Our data highlight a probable relationship between the allele CAG 22/GGC 17 and a defective spermatogenesis in infertile men, suggesting that these polymorphisms might have an important effect on AR function.

Non-linear association between androgen receptor CAG and GGN repeat lengths and reproductive parameters in fertile European and Inuit men

Recently the dogma that there is an inverse linear association between androgen receptor (AR) CAG and GGN polymorphisms and receptor activity has been challenged. We analysed the pattern of association between 21 male reproductive phenotypes and AR CAG/GGN repeat lengths in 557 proven-fertile men. A linear association was only found between sperm DNA fragmentation index (DFI) and CAG length, and between inhibin B and GGN length. Men with longer CAG then the reference (22-24), had higher oestradiol levels, whereas men with shorter CAG stretches had a higher DFI and a higher proportion of Fas-positive germ cells. Subjects with either short or long CAG had increased seminal levels of prostate-specific antigen and neutral α-glucosidase activity. Compared to men with the median GGN length of 23, those with shorter GGN repeats had higher levels of inhibin B, higher proportions of normal and progressive sperm, and a higher fraction of Fas-positive sperm, while men with longer GGN had higher oestradiol levels. These data indicate that at least for some markers of male reproductive function the association with CAG or GGN repeat length is curvilinear.

Androgen receptor-CAG repeats in infertile Egyptian men

This study aimed to assess the androgen receptor (AR) codon amino acids glutamine (CAG) repeats in 185 Egyptian men divided into fertile controls (n = 30), oligoasthenoteratozoospermic (OAT) men (n = 35), nonobstructive azoospermic (NOA) men (n = 120; 18 successful testicular sperm extraction (TESE) and 102 unsuccessful TESE cases). They were subjected to history taking, genital examination, semen analysis, testicular biopsies for NOA cases, serum hormones and CAG repeats by PCR. The mean AR-CAG repeats showed significant difference between NOA group compared with fertile controls or OAT groups. Nonsignificant difference was elicited between OAT group and fertile controls. In NOA cases, CAG repeats demonstrated nonsignificant difference between unsuccessful and successful TESE. AR-CAG repeats elicited significant negative correlation with sperm count, significant positive correlation with sperm normal forms percentage and nonsignificant correlations with sperm motility per cent, tested serum hormones or testicular volume. It is concluded that AR-CAG repeats in Egyptian infertile men are in the range of other international or regional studies. AR-CAG repeats have demonstrated nonsignificant difference regarding TESE outcome in NOA cases.

Gene copy number reduction in the azoospermia factor c (AZFc) region and its effect on total motile sperm count

The azoospermia factor c (AZFc) region harbors multi-copy genes that are expressed in the testis. Deletions of the AZFc region lead to reduced copy numbers of these genes. Four (partial) AZFc deletions have been described of which the b2/b4 and gr/gr deletions affect semen quality. In most studies, (partial) AZFc deletions are identified and characterized using plus/minus sequence site tag (STS) polymerase chain reaction (PCR). However, secondary duplications increase the gene copy number without re-introducing the STS boundary marker. Consequently, the actual copy number of AZFc genes cannot be determined via STS PCR. In the current study, we first set out to determine by quantitative real-time PCR the actual copy number of all AZFc genes in men with (partial) AZFc deletions based on STS PCR. We then analyzed whether reduced gene copy numbers of each AZFc gene family were associated with reduced total motile sperm count (TMC), regardless of the type of deletion. We screened 840 men and identified 31 unrelated men with (partial) deletions of AZFc based on STS PCR. Of these 31 men, 6 men (19%) had one or more secondary duplications. For all AZFc genes, we found an association between a reduction in the copy number of each individual AZFc gene and reduced TMC. In gr/gr-deleted men, restoration of reduced gene copy numbers restored their TMC to normal values. Our findings suggest that the gene content of the AZFc region has been preserved throughout evolution through a dosage effect of the AZFc genes on TMC safeguarding male fertility.

Unravelling the genetics of spermatogenic failure

Subfertility, defined as the inability to conceive within 1 year of unprotected intercourse, affects 10–15% of couples. In up to 55% of couples, the male partner is diagnosed with spermatogenic failure, i.e. one or more semen parameters fall below the WHO criteria for normozoospermia. In these cases, assisted reproductive technology is usually used to achieve pregnancy. Both genetic and environmental factors are thought to underlie spermatogenic failure. Despite years of research, only few genetic factors have clearly been shown to cause spermatogenic failure, and the identification of additional genetic causes or risk factors has proven to be extremely difficult. In this review, we will present an overview of established genetic causes of spermatogenic failure, describe pitfalls in searching for novel genetic factors and discuss research opportunities for the future.

The COX-2 promoter polymorphism -765 G>C is associated with early-onset, conventional and stump gastric cancers

COX-2 overexpression is known to be an important mechanism in gastric carcinogenesis. Previously we have found that early-onset gastric cancer has a unique COX-2 low-expressing phenotype that differs significantly from that of the frequent overexpression seen in conventional gastric cancers. To investigate whether the COX-2 -765 G>C promoter polymorphism (known to lead to a reduction of COX-2 promoter activity in the colon) may explain this difference in expression, we carried out single-nucleotide polymorphism (SNP) analysis of 241 gastric cancers, including early-onset gastric cancer, conventional gastric cancers and gastric stump cancers, as well as in 100 control patients, using real-time PCR and sequence analysis, and correlated these findings with COX-2 expression using immunohistochemistry. We found that the C allele was present in 30% of early-onset gastric cancers, 24% of conventional gastric cancer, 23% of stump cancers, in contrast to 41% in the control group. There was a statistically significant difference in the presence of the C allele in patients with gastric cancer compared with the control group (P=0.007), with the C allele being associated with protection against gastric cancer. However, there was no significant difference between the early-onset, conventional and stump gastric cancer groups. Interestingly, there was no correlation between the presence of the C allele and a difference in COX-2 expression. In summary, we show that the COX-2 -765 G allele promoter polymorphism is significantly associated with gastric cancer when compared with the normal control group, but does not appear to be related directly to COX-2 expression pattern in gastric cancer. Although early-onset gastric cancers appear to have a unique COX-2 expression pattern when compared with conventional gastric cancer, the exact mechanism by which this occurs is yet to be elucidated.