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.

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

Male infertility is a multi-factorial and multi-genetic disorder, and the prevalence of male infertility in the world is estimated at 5–35%. The search for the causes of male infertility allowed for identifying a number of genetic factors including a single X-linked gene of the androgen receptor (AR), and some of its alleles are assumed to negatively affect male fertility. Our aim was (1) to study the variability of the length of CAG repeats of the AR gene and possible associations in the AR CAG genetic variants with semen quality and reproductive hormone levels in a population-based cohort of men and (2) to estimate distributions of AR CAG repeat alleles and associations with semen parameters in different ethnic subgroups. The cohort of 1324 young male volunteers of different ethnicities (median age 23.0 years) was recruited from the general population of five cities of the Russian Federation, regardless of their fertility status. Semen quality (sperm concentration, motility and morphology), reproductive hormone levels (testosterone, estradiol, LH, FSH and inhibin B) and trinucleotide (CAG) n repeat polymorphism in exon 1 of the AR gene were evaluated. The semen samples were analyzed according to the WHO laboratory manual (WHO, 2010), serum hormones were measured by enzyme immunoassay, and the AR CAG repeat length was analyzed by direct sequencing of leukocyte DNA. The median AR CAG repeat length in men of our multi-ethnic population was 23 (range 6–39). In the entire study population, a significant difference (p ≤ 0.05) was found in the frequency distribution and the mean values for the CAG repeat length between the groups with normal (23.2 ± 3.3) and impaired semen quality (23.9 ± 3.2). Additionally, we demonstrated that the total sperm count, sperm concentration, progressive motility and normal morphology were lower in the category of long CAG repeats (CAG ≥ 25) compared with those in the category of short CAG repeats (CAG ≤ 19); however, hormonal parameters did not differ between the long and short CAG categories, with the exception of estradiol. Significant differences were observed in the AR CAG repeat length between the most common ethnic cohorts of Slavs (Caucasians), Buryats (Asians), and Yakuts (Asians). The Buryats and Yakuts had a higher number of CAG repeats than the Slavs (medians: Slavs—23; Buryats—24; Yakuts—25). The range of alleles differed among ethnicities, with the Slavs having the largest range (7–36 repeats, 24 alleles total), the Yakuts having the smallest range (18–32 repeats, 14 alleles total) and the Buryats having the middle range (11–39 repeats, 20 alleles total). The longer CAG repeats were associated with an impaired semen quality within the Slavic (CAG ≥ 25) and Buryat (CAG ≥ 28) groups, but this effect was not found in Yakuts. Hormonal parameters did not differ between the three CAG repeat categories in men of all ethnic groups. This is the largest Russian study of the distribution of AR CAG repeats and the search for association between length of AR CAG repeat tract and impaired spermatogenesis in men from the general population. Our results confirmed the association of longer CAG repeats with a risk of impaired semen quality, but this association can be modified by ethnic origin. Identification of the number of AR CAG repeats can be an effective tool to assess the risk of male subfertility and the control of androgen hormone therapy of reproductive diseases.