Androgen receptor gene polyglutamine length is associated with testicular histology in infertile patients

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.

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.

The relationship between anogenital distance and the androgen receptor CAG repeat length

Anogenital distance (AGD) is used to define degree of virilization of genital development, with shorter length being associated with feminization and male infertility. The first exon of the androgen receptor (AR) consists of a polymorphic sequence of cytosine-adenine-guanine (CAG) repeats, with longer CAG repeat lengths being associated with decreased receptor function. We sought to determine if there is an association between AGD and AR CAG repeat length. A cross-sectional, prospective cohort of men evaluated at a urology clinic at a single institution was recruited. AGD (the distance from the posterior scrotum to the anal verge) and penile length (PL) were measured. Sanger DNA sequence analysis was used to define CAG repeat length. AGD and CAG repeat lengths in 195 men were determined. On unadjusted analysis, there was no linear relationship between CAG repeat length and PL (P=0.17) or AGD (P=0.31). However, on sub-population analyses, those men with longer CAG repeat lengths (>26) had significantly shorter AGDs compared to men with shorter CAG repeat lengths. For example, the mean AGD was 41.9 vs. 32.4 mm with a CAG repeat length ≤26 vs. >26 (P=0.01). In addition, when stratifying the cohort based on AGD, those with AGD less than the median (i.e. 40 mm) had a longer CAG repeat length compared to men with an AGD >40 mm (P=0.02). In summary, no linear relationship was found between AGD and AR CAG repeat length overall.

The epidemiology and etiology of azoospermia

The misconception that infertility is typically associated with the female is commonly faced in the management of infertile men. It is uncommon for a patient to present for an infertility evaluation with an abnormal semen analysis report before an extensive female partner workup has been performed. Additionally, a man is usually considered fertile based only on seminal parameters without a physical exam. This behavior may lead to a delay in both the exact diagnosis and in possible specific infertility treatment. Moreover, male factor infertility can result from an underlying medical condition that is often treatable but could possibly be life-threatening. The responsibility of male factor in couple's infertility has been exponentially rising in recent years due to a comprehensive evaluation of reproductive male function and improved diagnostic tools. Despite this improvement in diagnosis, azoospermia is always the most challenging topic associated with infertility treatment. Several conditions that interfere with spermatogenesis and reduce sperm production and quality can lead to azoospermia. Azoospermia may also occur because of a reproductive tract obstruction. Optimal management of patients with azoospermia requires a full understanding of the disease etiology. This review will discuss in detail the epidemiology and etiology of azoospermia. A thorough literature survey was performed using the Medline, EMBASE, BIOSIS, and Cochrane databases. We restricted the survey to clinical publications that were relevant to male infertility and azoospermia. Many of the recommendations included are not based on controlled studies.

Non-linear association between androgen receptor CAG repeat length and risk of male subfertility--a meta-analysis

The CAG repeat in the androgen receptor (AR) has been widely studied in association with male infertility, but the results are conflicting. In a recent meta-analysis, infertile men had <1 repeat longer CAG stretch than fertile men when analysed in a linear regression model assuming that AR function diminishes with increasing CAG length. However, in vitro, a non-linear activity pattern was recently demonstrated so that ARs containing short and long stretches, respectively, displayed lower activity than the AR of median length. These results prompted us to explore the possible association between CAG number and male infertility risk in a stratified manner on the basis of data from the mentioned meta-analysis and subjects from our clinical unit. The study population included 3915 men, 1831 fertile and 2084 infertile. Data were divided into three categories: CAG<22, CAG 22-23 (reference) and CAG>23 and analysed in a binary logistic regression model. Men with CAG<22 and CAG>23 had 20% increased odds ratio of infertility compared with carriers of the median lengths [for CAG<22: p=0.03, 95% confidence interval (CI): 1.02-1.39; for CAG>23: p=0.02, 95% CI: 1.03-1.44]. These results show that an alternative model to a linear one for the genotype-phenotype association in relation to AR CAG repeats is likely, as lengths close to the median confine lowest risk of infertility.

Evidence for association of sex hormone-binding globulin and androgen receptor genes with semen quality

The roles of androgen receptor AR(CAG)n gene polymorphisms and sex hormone-binding globulin SHBG(TAAAA)n gene polymorphisms on semen quality were studied. One hundred fourteen men were included in the study: 85 with normal sperm count and 29 oligospermic. The genotype analysis, on DNA extracted from spermatozoa, revealed five SHBG(TAAAA)n alleles with 6-10 repeats and 18 AR(CAG)n alleles with 12-32 repeats. The SHBG allelic distribution showed that in men with normal sperm count and motility, those with short SHBG alleles had higher sperm concentration than men with long SHBG alleles (P = 0.039). As concerns AR(CAG)n polymorphisms, men with short AR alleles had lower sperm motility compared to those with long AR alleles (P < 0.001) in both total study population and normal sperm count men. The synergistic effect analysis of the two polymorphisms revealed an association between sperm motility (P = 0.036), because of the effect of AR(CAG)n polymorphism on sperm motility. In conclusion, long AR alleles were found to be associated with higher sperm motility, while short SHBG alleles were associated with higher sperm concentration, supporting the significance of these genes in spermatogenesis and semen quality.

Androgen receptor and Kennedy disease/spinal bulbar muscular atrophy

Kennedy Disease/Spinal Bulbar Muscular Atrophy (KD/SBMA) is a progressive neurodegenerative disease caused by genetic polyglutamine expansion of the androgen receptor. We have recently found that overexpression of wildtype androgen receptor in skeletal muscle of transgenic mice results in a KD/SBMA phenotype. This surprising result challenges the orthodox view that KD/SBMA requires expression of polyglutamine expanded androgen receptor within motoneurons. Theories relating to the etiology of this disease drawn from studies of human patients, cellular and mouse models are considered with a special emphasis on potential myogenic contributions to as well as the molecular etiology of KD/SBMA.

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

Previous association studies that described the effect of an enlarged CAG repeat length in the Androgen Receptor (AR) gene on spermatogenesis could not prove or refute a true association because of methodological weaknesses. Here, we clearly show that there is no association between CAG repeat length variation and semen quality.

Male infertility and variation in CAG repeat length in the androgen receptor gene: a meta-analysis

CONTEXT

Many studies have investigated the association between male infertility and trinucleotide repeat polymorphisms in the androgen receptor (AR) gene, but no comprehensive meta-analysis of all published studies has been conducted.

OBJECTIVE

Our goals were to summarize published data on associations between AR CAG and GGC repeat lengths and male infertility and investigate sources of variation between study results.

DATA SOURCES

We searched for reports published before October 2006 using Medline, PubMed, and Web of Science.

STUDY SELECTION

All selected studies included the following: a case group with infertility as measured by semen parameters, a control group of known or presumed fertile men, and measurement of CAG and/or GGC repeat lengths among cases and controls. Thirty-nine reports were selected based on these criteria, and 33 were ultimately included in the meta-analysis.

DATA EXTRACTION

One investigator extracted data on sample size, mean and sd of trinucleotide repeat length, and study characteristics.

DATA SYNTHESIS

Estimates of the standardized mean difference (95% confidence interval) were 0.19 (0.09-0.29) for the 33 studies and 0.31 (0.14-0.47) for a subset of 13 studies that used more stringent case and control selection criteria. Thus, in both groups, cases had statistically significantly longer CAG repeat length than controls. Publication date appeared to be a significant source of variation between studies.

CONCLUSIONS

This meta-analysis provides support for an association between increased androgen receptor CAG length and idiopathic male infertility, suggesting that even subtle disruptions in the androgen axis may compromise male fertility.

Phenotypic heterogeneity of mutations in androgen receptor gene

Androgen receptor (AR) gene has been extensively studied in diverse clinical conditions. In addition to the point mutations, trinucleotide repeat (CAG and GGN) length polymorphisms have been an additional subject of interest and controversy among geneticists. The polymorphic variations in triplet repeats have been associated with a number of disorders, but at the same time contradictory findings have also been reported. Further, studies on the same disorder in different populations have generated different results. Therefore, combined analysis or review of the published studies has been of much value to extract information on the significance of variations in the gene in various clinical conditions. AR genetics has been reviewed extensively but until now review articles have focused on individual clinical categories such as androgen insensitivity, male infertility, prostate cancer, and so on. We have made the first effort to review most the aspects of AR genetics. The impact of androgens in various disorders and polymorphic variations in the AR gene is the main focus of this review. Additionally, the correlations observed in various studies have been discussed in the light of in vitro evidences available for the effect of AR gene variations on the action of androgens.

The CAG repeat within the androgen receptor gene and its relationship to cryptorchidism

PURPOSE

We examined the significance of the CAG repeat polymorphism in the pathogenesis of cryptorchidism.

MATERIALS AND METHODS

Genomic deoxyribonucleic acid (DNA) was extracted from blood samples from 42 cryptorchid boys and from 31 non-cryptorchid control subjects. In the cryptorchid group, 7 had bilateral cryptorchidism and 6 had patent processus vaginalis in the contralateral side. To determine the number of CAG repeats, the DNA was amplified by polymerase chain reaction and sequenced.

RESULTS

The mean CAG repeat length in the AR gene was 22.5 (range 16 to 28) in patients and 21.5 (range 17 to 26) in controls (non-significant). Patients with bilateral cryptorchidism had a mean length of 24.3 (range 21 to 26) and patients with unilateral cryptorchidism and patent processus vaginalis in the contra lateral side had a mean of 25.2 (range 21 to 28), which was statistically different from controls (p = 0.015 and p = 0.005 respectively).

CONCLUSION

CAG repeat length of the AR gene does not seem to play a major role in patients with unilateral cryptorchidism. However, in patients with bilateral undescended testis, a less functional androgen receptor through a longer polyglutamine chain may have a role in its pathogenesis. In the same way, patients with unilateral cryptorchidism a contralateral patent processus vaginalis have longer CAG repeats that might be responsible for a slower testicular descent and incomplete closure of the processus vaginalis.

No association of the CAG repeat length in exon 1 of the androgen receptor gene with idiopathic infertility in Turkish men: implications and literature review

While the correlation between the CAG repeat length of the androgen receptor (AR) gene and idiopathic male infertility is still unclear, ethnic background of the population studied may play an important role in this association. The objective of this study was to determine whether changes in the CAG repeat length are associated with spermatogenic defects in Turkish infertile men. Reproductive hormone concentrations and the CAG repeat length in exon 1 of the AR gene in 47 idiopathic infertile men and 32 fertile controls were analyzed. The mean serum luteinising hormone (LH) and follicle stimulating hormone (FSH) levels were significantly higher in the infertile group than those of the control group (p < 0.0001 for both comparisons), whereas the mean serum testosterone level in the infertile group did not differ significantly from that in the control group (p = 0.16). The mean CAG repeat length of the AR gene in the infertile group did not differ significantly from that in the control group (22.28 +/- 0.37 vs 22.41 +/- 0.54, respectively; p = 0.84). In addition, the frequency of having a CAG repeat number (> or = 24) was also comparable between the infertile patients and fertile controls (31.9% vs 40.6%, respectively; p = 0.21). In conclusion, reproductive hormones with elevated LH and FSH, and normal or low testosterone levels were suggestive of partial impairment of testicular function. However, no statistically significant relationship between the length of the CAG repeat and idiopathic impaired sperm production was observed in the Turkish population studied. These results support the findings of previously published European studies, but are contrary to the findings from Caucasian and North American population studies. Thus, ethnicity and genetic backgrounds seem to be important in this association, and studies from a variety of different ethnic and genetic backgrounds using comparable patient subgroups are valuable to further evaluate this association.

Androgen receptor gene CAG and GGC repeat lengths in cryptorchidism

OBJECTIVE

Cryptorchidism is the most common congenital birth defect in male children, and accumulating evidence suggests that genetic abnormalities may be associated with it. The androgen receptor has two polymorphic sites in exon 1, with different numbers of CAG and GGC repeats, resulting in variable lengths of polyglutamine and polyglycine stretches. Longer CAG repeats result in a reduced androgen receptor transcriptional activity, but the role of the GGC triplets is less clear. In this study we analysed CAG and GGC repeat lengths in men with a history of cryptorchidism, associated or not with impairment of sperm production, in comparison with normal fertile subjects.

METHODS

We analysed CAG and GGC repeat lengths in a group of 105 ex-cryptorchid men in comparison with 115 fertile non-cryptorchid men.

RESULTS

No difference was found between patients and controls in the mean and median values, and in distribution of CAG and GGC, when considered separately. However, the analysis of the joint distribution of CAG and GGC showed that some combinations are significantly more frequent in men with bilateral cryptorchidism (who frequently presented severe testiculopathies), in a manner similar to that found in idiopathic infertile subjects.

CONCLUSIONS

Although further studies are needed to elucidate the possible role of specific CAG/GGC combinations as a causative factor, these data suggest a possible association between androgen receptor gene polymorphisms and cryptorchidism.

Molecular pathology of the androgen receptor in male (in)fertility

Idiopathic male infertility, accounting for 40% of all male infertility cases, is postulated to have a genetic basis. The androgen receptor (AR) plays a crucial post-meiotic role during male germ cell differentiation, which includes terminal differentiation of spermatids and their release from the seminiferous epithelium. Mutations in the AR gene result in a condition known as androgen insensitivity syndrome (AIS) affecting normal male morphogenesis. Depending on the severity of the syndrome, the external phenotype can range from normal female to normal male. In almost all cases affected individuals are infertile. In seven reported cases individuals appeared to suffer primarily or solely from male infertility, suggesting these AR mutations specifically cause male infertility. Three of these mutations are possibly population specific. Longer CAG repeats present in exon 1 of the AR have been studied as a possible risk factor for male infertility. Results are contradictory, with a trend to significance (Asian populations) and non-significance (European populations). Recent advances in protein modelling techniques may result in a much better understanding of the mechanism of action of the known infertility mutations. The determination of the significance of longer CAG repeats is likely to require studies that examine CAG repeat lengths in spermatozoa as well as patients' blood.

The androgen receptor gene mutations database (ARDB): 2004 update

The current version of the androgen receptor (AR) gene mutations database is described. The total number of reported mutations has risen from 374 to 605, and the number of AR-interacting proteins described has increased from 23 to 70, both over the past 3 years. A 3D model of the AR ligand-binding domain (AR LBD) has been added to give a better understanding of gene structure-function relationships. In addition, silent mutations have now been reported in both androgen insensitivity syndrome (AIS) and prostate cancer (CaP) cases. The database also now incorporates information on the exon 1 CAG repeat expansion disease, spinobulbar muscular atrophy (SBMA), as well as CAG repeat length variations associated with risk for female breast, uterine endometrial, colorectal, and prostate cancer, as well as for male infertility. The possible implications of somatic mutations, as opposed to germline mutations, in the development of future locus-specific mutation databases (LSDBs) is discussed. The database is available on the Internet (http://www.mcgill.ca/androgendb/).