Androgen Receptor Gene CAG Repeat Length Varies and Affects Semen Quality in an Ethnic-Specific Fashion in Young Men from Russia

Androgen receptor CAG repeat polymorphism might be a possible cause of familial constitutional delay of growth and puberty

BACKGROUND

Induction of puberty in boys with constitutional delay of growth and puberty (CDGP) through a short course of low-dose testosterone therapy indicates the critical interaction between testosterone and the androgen receptor (AR) during the activation and maturation of the hypothalamic-pituitary-gonadal axis at puberty onset. Previous studies have shown an inverse relationship between the CAG repeat length and the transactivation function or expression level of the AR gene.

OBJECTIVE

We aimed to investigate whether the AR CAG repeat polymorphism has any implications on pubertal delay.

SUBJECTS AND METHODS

Thirty-three male patients with CDGP were enrolled in the study group, while 53 age-matched healthy individuals who had entered puberty on time were included in the control group. The CAG repeat length was determined through direct DNA sequencing analysis.

RESULTS

The median chronological age of boys with CDGP was 14.2 (14.1-14.6) years, compared to 14.2 (13.65-14.8) years for healthy subjects (p = 0.5). In the CDGP group, 22 (66.7%) children had a family history of the condition. There was no significant difference between the groups in terms of AR CAG repeat length (median AR CAG repeat length: 21 (20-24.5) and 20 (20-24), respectively, p = 0.1). However, in boys with CDGP with a similar family history (n = 22), a significantly longer AR CAG repeat length was found compared to the control group (n = 53) (median AR CAG repeat length: 22 (20-25) and 20 (20-24), respectively, p = 0.03). The median AR CAG repeat length in boys without a family history was 21 (20-22) triplets. Although boys with a family history had a slightly longer AR CAG repeat length than those without, the difference was not statistically significant (p = 0.07). Additionally, no significant differences were observed between boys with non-familial CDGP and control subjects (p = 0.8). Furthermore, no significant differences in anthropometric characteristics or hormonal parameters were found when patients with CDGP were categorized by AR CAG repeat length quartiles.

CONCLUSION

This is the first study to investigate the role of AR CAG polymorphism in the etiopathogenesis of CDGP. Our findings suggest that the AR CAG repeat length may be associated with familial CDGP.

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.

Prevalence of AZFс Y chromosome microdeletions and association with spermatogenesis in Russian men from the general population

The Y chromosome contains a set of genes with testis-specific expression that are responsible for the development of testes and spermatogenesis, and it is the most important target in the search for genetic causes of male infertility. Most of these genes are located in the "azoospermia factor" AZF locus (regions AZFa, AZFb, and AZFc) on the long arm of the Y chromosome. Microdeletions of the Y chromosome, leading to the removal of the entire AZF locus as well as one or more regions (complete deletions), are one of the leading causes of spermatogenesis impairment and infertility. However, the role of partial AZFc deletions (gr/gr, b2/b3, b1/b3) in spermatogenesis failure is unclear, and their impact on spermatogenesis varies between populations. The aim of the present study was to assess the frequency of various types of AZFc microdeletions and to search for associations with spermatogenesis parameters in men of Slavic ethnicity from the general Russian population (n = 700, average age 25.8 years). To identify AZF microdeletions, the presence/absence of 15 STS markers was analyzed using multiplex real-time polymerase chain reaction. Age, weight, height, and the volume, concentration, total count, proportion of motile and morphologically normal spermatozoa in the ejaculate were recorded for all participants. In the studied sample, 19.9 % (139/700) of men were found to have AZFc microdeletions, of which 16.7 % (117/700) were carriers of a partial b2/b3 deletion, 3.0 % (21/700) had a partial gr/gr deletion, and 0.14 % (1/700) had a complete b2/b4 deletion. Neither AZFa nor AZFb microdeletions nor other types of AZF deletions were detected. The overall frequency of all types of AZFc deletions, as well as each type of partial microdeletion, b2/ b3 and gr/gr, did not differ in the groups of azoospermia, severe oligozoospermia (≤5.0 mill/ml), oligozoospermia (5.0 < SC <16.0 mill/ml), and normal sperm concentration (≥16.0 mill/ml). Comparison of semen parameters in groups with different types of partial AZFc deletions and the control group (without deletions) also did not reveal significant differences. Thus, partial AZFc microdeletions b2/b3 and gr/gr do not have a significant impact on spermatogenesis in Slavic men. It is suggested that in Slavs, partial AZFc microdeletions b2/b3 and gr/gr are fixed in Y haplogroups N3 and R1a, respectively, and their negative impact on spermatogenesis is balanced by other genetic factors. The higher frequency of partial AZFc deletions (19.7 %) in Slavs compared to European populations (7.3 %) established in our study may be explained by the widespread distribution of these Y haplogroups in the Slavic population of Russia.

Fluctuations in Medium Viscosity May Affect the Stability of the CAG Tract in the ATXN2 Gene

Background: Trinucleotide repeats are the cause of many neurodegenerative diseases that are currently incurable. In this regard, the question of the causes of occurrence and methods of prevention or treatment of diseases caused by the expansion of repeats in the CAG tract of the ATXN2 gene remains relevant. Previously, it was shown that the frequency of occurrence of additional OS (open states) zones increases with increasing length of the CAG tract, and the value inverse to the frequency correlates with the age of disease onset. Methods: In this work, the influence of the viscosity of the medium and the external torque on the stability of the CAG tract in the ATXN2 gene was studied using mathematical modeling methods. Results: It has been established that the probability of the appearance of additional OS zones of significant size increases with an increase in the CAG of the tract (k > 40 CAG repeats) for all viscosity values, however, at k ≤ 40, the change in viscosity does not significantly affect the probability of additional OS zones in the tract. Conclusions: It was found that under normal conditions (absence of pathology), viscosity does not have a reliable effect on the stability of the DNA molecule, but when pathology appears, an increase in viscosity contributes to an increase in DNA stability, and, accordingly, a decrease has a negative effect on the stabilization of the DNA molecule. In the zone of close to incomplete penetrance of the disease, viscosity does not have a reliable effect on the stability of the CAG tract.

Associations of CAG repeat polymorphism in the androgen receptor gene with steroid hormone levels and anthropometrics among men: the role of the ethnic factor

Androgens are required for stimulation and maintenance of skeletal growth and bone homeostasis. Physiological functions of androgens are mediated through the androgen receptor (AR). The androgen receptor gene AR has a polymorphic trinucleotide CAG repeat and the length of AR CAG repeats determining the sensitivity of bone tissue to androgens is associated with skeleton formation and body proportions. This study aimed to investigate the relationship between AR CAG repeat polymorphism, circulating sex steroid hormones and the anthropometrics in males of different ethnic origins. Male volunteers of three ethnic groups (Slavs, Buryats, Yakuts) from urban Russian populations were recruited in a population-based study (n = 1078). Anthropometric indicators (height, arm span, leg length, the length of 2 and 4 digits of both hands) were measured and the following anthropometric indices were calculated: the ratio of height to leg length, the ratio of arm span to height, the ratio of lengths of second to fourth digit of the hand. Serum testosterone and estradiol were determined by enzyme immunoassay. Genotyping of the AR CAG repeats was performed using fragment analysis and capillary electrophoresis. Ethnic differences in all anthropometric and hormonal indicators have been established, with higher anthropometric indicators in Slavs than Buryats, and in most cases higher than in Yakuts. The testosterone level was higher among Slavs compared to Buryats, but did not differ from Yakuts; the estradiol level was lower among Slavs compared to Buryats, who did not differ from Yakuts. Buryats and Yakuts had a higher number of CAG repeats than Slavs (medians: Slavs, 23; Buryats, 24; Yakuts, 25). Positive correlations were found between the length of AR CAG repeats and estradiol levels in Buryats and testosterone levels in Yakuts, while longer CAG repeats were accompanied by higher estradiol levels in Buryats and testosterone levels in Slavs and Yakuts. Ethnic-specific correlations have been established between the steroid hormone levels and some anthropometric indicators in all ethnic groups. Available data suggest that the ethnic-specific associations of AR CAG repeats with anthropometrics can be mediated by sex steroid hormones as important regulators of skeletal growth and bone homeostasis.

Effects of cigarette smoking on semen quality, reproductive hormone levels, metabolic profile, zinc and sperm DNA fragmentation in men: results from a population-based study

Background

Cigarette smoking seems to have a negative impact on men's reproductive health, but our knowledge of its effects on the reproductive function of Russian men is still very limited. The purpose of this study was to evaluate the effect of cigarette smoking on semen quality, including sperm DNA fragmentation, hormonal, zinc and metabolic status in young men from the general multi-ethnic Russian population (n=1,222, median age 23 years) and to find out the ethno-specific effects of smoking by comparing male groups of different ethnicity.

Methods

Each participant filled out a standardized questionnaire, provided one blood and semen sample. Semen parameters, serum reproductive hormones, lipids, glucose, uric acid and seminal zinc were analyzed. Participants were classified as smokers (n=450) and non-smokers (n=772), and smokers were stratified into moderate (≤10 cigarettes/day) and heavy (>10 cigarettes/day) smokers.

Results

In the entire study population, heavy smokers were characterized by a decrease in semen volume, total sperm count, sperm concentration and motility, and an increase in sperm DNA fragmentation and teratozoospermia compared with non-smokers (p<0.05). There was also a reduction in the serum and seminal zinc level as well as an impairment in metabolic health in smokers compared with non-smokers (p<0.05). No significant differences between smokers and non-smokers were found for serum levels of LH, FSH, inhibin B, testosterone and estradiol. In the second part of our study, the most numerous ethnic groups of Slavs (n=654), Buryats (n=191), and Yakuts (n=125) were selected from the entire study population. Among three ethnic groups, the smoking intensity was higher in Slavs than in Buryats or Yakuts suggesting a greater tobacco addiction in Slavs than in Asians. A decrease in semen parameters and seminal zinc levels, and an increase in sperm DNA fragmentation and teratozoospermia was observed only in smoking Slavs (p<0.05); moderate decrease in testosterone and increase in triglyceride levels were revealed in smoking Yakuts (p<0.05), but no significant changes were detected in smoking Buryats.

Conclusion

We concluded that cigarette smoking has an ethno-specific effect on male reproductive function, probably due to the different activity of the seminal antioxidant system, which is yet to be elucidated.

Native functions of short tandem repeats

Over a third of the human genome is comprised of repetitive sequences, including more than a million short tandem repeats (STRs). While studies of the pathologic consequences of repeat expansions that cause syndromic human diseases are extensive, the potential native functions of STRs are often ignored. Here, we summarize a growing body of research into the normal biological functions for repetitive elements across the genome, with a particular focus on the roles of STRs in regulating gene expression. We propose reconceptualizing the pathogenic consequences of repeat expansions as aberrancies in normal gene regulation. From this altered viewpoint, we predict that future work will reveal broader roles for STRs in neuronal function and as risk alleles for more common human neurological diseases.