Lack of influence of the androgen receptor gene CAG-repeat polymorphism on sex steroid status and bone metabolism in elderly men

Bone health in ageing men

Osteoporosis does not only affect postmenopausal women, but also ageing men. The burden of disease is projected to increase with higher life expectancy both in females and males. Importantly, osteoporotic men remain more often undiagnosed and untreated compared to women. Sex steroid deficiency is associated with bone loss and increased fracture risk, and circulating sex steroid levels have been shown to be associated both with bone mineral density and fracture risk in elderly men. However, in contrast to postmenopausal osteoporosis, the contribution of relatively small decrease of circulating sex steroid concentrations in the ageing male to the development of osteoporosis and related fractures, is probably only minor. In this review we provide several clinical and preclinical arguments in favor of a 'bone threshold' for occurrence of hypogonadal osteoporosis, corresponding to a grade of sex steroid deficiency that in general will not occur in many elderly men. Testosterone replacement therapy has been shown to increase bone mineral density in men, however data in osteoporotic ageing males are scarce, and evidence on fracture risk reduction is lacking. We conclude that testosterone replacement therapy should not be used as a sole bone-specific treatment in osteoporotic elderly men.

Ageing male (part I): Pathophysiology and diagnosis of functional hypogonadism

This narrative review summarizes key points of the pathogenesis and diagnosis of the ageing-related decline of testosterone (T) in men. The condition is commonly termed late-onset hypogonadism (LOH), but because it is more often caused by other factors than chronological ageing (obesity and other comorbidities), a more appropriate term is functional hypogonadism (FH). Unlike the classical organic hypogonadism, no anatomical or genetic aberrations are found in FH, and the suppression of T is milder. Moreover, FH can be reversible if the underlying cause (e.g. obesity, chronic disease) is removed/treated. Low serum total T in connection with more specific hypogonadism-associated symptoms (primarily sexual) form the basis of the diagnosis of FH. When T concentrations are borderline, the accuracy of diagnosis can be improved by assessment of free or calculated free T, especially when suppressed SHBG levels (usually related to obesity) are likely. Current data indicate that FH (low T and sexual symptoms) is not a common condition, and it is detectable in about 2% of community-dwelling men aged 40-80 years.

Androgen receptor CAG repeat length as a moderator of the relationship between free testosterone levels and cognition

Age-related decrease in testosterone levels is a potential risk factor for cognitive decline in older men. However, observational studies and clinical trials have reported inconsistent results on the effects of testosterone on individual cognitive domains. Null findings may be attributed to factors that studies have yet to consider. In particular, individual variations in polyglutamine (CAG) length in the androgen receptor (AR) gene could alter androgenic activity in brain regions associated with cognitive processes including memory and executive functions. However, the role of AR CAG repeat length as a moderator of the relationship between testosterone levels and cognition has not been investigated. Therefore, we aimed to examine the relationship between baseline calculated free testosterone (cFT) levels, change in cFT levels over 18 months and CAG repeat length on cognitive performance in memory, executive function, language, attention and processing speed domains. These relationships were examined in 304 cognitively normal older male participants of the Australian Imaging, Biomarkers and Lifestyle (AIBL) Study of Ageing. In the attention and processing speed domain, a short CAG repeat length appears to exacerbate the effects of low baseline cFT levels that are also lower than expected at follow-up. These results highlight that individual variations in AR CAG repeat length should be considered in future studies and clinical trials that examine the complex relationship between testosterone and cognition.

Aging and the Male Reproductive System

This narrative review presents an overview of current knowledge on fertility and reproductive hormone changes in aging men, the factors driving and modulating these changes, their clinical consequences, and the benefits and risks of testosterone (T) therapy. Aging is accompanied by moderate decline of gamete quality and fertility. Population mean levels show a mild total T decline, an SHBG increase, a steeper free T decline, and a moderate LH increase with important contribution of comorbidities (e.g., obesity) to these changes. Sexual symptoms and lower hematocrit are associated with low T and are partly responsive to T therapy. The relationship of serum T with body composition and metabolic health is bidirectional; limited beneficial effects of T therapy on body composition have only marginal effects on metabolic health and physical function. Skeletal changes are associated primarily with estradiol and SHBG. Cognitive decline is not consistently linked to low T and is not improved by T therapy. Although limited evidence links moderate androgen decline with depressive symptoms, T therapy has small beneficial effects on mood, depressive symptoms, and vitality in elderly patients with low T. Suboptimal T (and/or DHT) has been associated with increased risk of stroke, but not of ischemic heart disease, whereas an association with mortality probably reflects that low T is a marker of poor health. Globally, neither severity of clinical consequences attributable to low T nor the nature and magnitude of beneficial treatment effects justify the concept of some broadly applied "T replacement therapy" in older men with low T. Moreover, long-term safety of T therapy is not established.

Androgen Receptor CAG Repeat Length as a Risk Factor of Late-Onset Hypogonadism in a Korean Male Population

Background

Testosterone action is mediated through the androgen receptor (AR), whose sensitivity is influenced by the AR CAG repeat polymorphism. However, the relation between late-onset hypogonadism (LOH) and AR CAG repeat length is unclear and studies of Asian populations are limited.

Aim

To investigate the relation between AR CAG repeat length and LOH in Korean men.

Methods

263 Korean men (mean age = 63.43 ± 10.9 years) were enrolled from 2014 to 2015. LOH diagnosis was based on a serum testosterone level lower than 3.5 ng/mL and positive androgen deficiency according to the Aging Males’ Symptom Scale (AMS). Total testosterone levels and answers to the LOH-related questionnaire were analyzed.

Outcomes

The relation between AR CAG repeat length and LOH was determined.

Results

Mean CAG repeat length was 22.1 ± 4.6 and mean serum testosterone levels were 2.6 ± 0.7 and 6.0 ± 2.0 ng/mL in men with and without LOH, respectively. Men with LOH showed significantly longer AR CAG repeat lengths than men without LOH (26.1 vs 21.6, P < .001). Longer CAG repeat lengths were correlated with higher AMS total scores (r = 0.454, P = .001) and AMS psychotic, somatic, and sexual sub-scores (r = 0.276, 0.246, and 0.571, P = .006, .007, .001, respectively) and significantly lower 5-item International Index of Erectile Function scores (r = −0.261, P = .001). Multivariate analysis showed that patient age and CAG repeat length were independently associated with LOH (odds ratio = 1.05 and 1.29, P = .041 and <.001, respectively).

Clinical Implications

A longer CAG repeat length is associated with LOH symptoms and LOH.

Strengths and Limitations

Associations between CAG repeats and LOH were verified in Korean patients. Moreover, a longer CAG repeat length was shown to be an independent risk factor for LOH. Limitations included the small number of LOH patients studied and that other sex hormone-associated factors were not measured.

Conclusions

AR CAG repeat length was associated with LOH prevalence and clinical symptoms in this Korean male population. Thus, it is important to measure CAG repeat length for patients with LOH symptoms with normal testosterone levels.

Kim JW, Bae YD, Ahn ST, et al. Androgen Receptor CAG Repeat Length as a Risk Factor of Late-Onset Hypogonadism in a Korean Male Population. Sex Med 2018;6:203–209.

Androgen receptor CAG repeat polymorphism is not associated with insulin resistance and diabetes among South Asian males

Objective

To study relationship between androgen receptor (AR) CAG repeat polymorphism, insulin resistance (IR), β-cell function and other clinical/biochemical parameters in ethnic South Asian adults. A case (males with diabetes), control (males without diabetes) study, was conducted and 110 males were invited. Anthropometry, blood pressure and biochemical parameters (fasting Insulin, blood sugar, HbA1c and lipid profile) were measured. IR and β-cell function was calculated. A multiple-linear-regression analysis was performed, using number of AR CAG repeats as the continuous dependent variable.

Results

Sample size was 100 (response rate—90.9%, cases—53). Mean age was 49.6 ± 10.7 years. CAG repeat length did not show any significant correlation with IR or β-cell function. In all males there was a significant correlation between number of AR CAG repeats and systolic blood pressure (r = 0.25; p = 0.016), diastolic blood pressure (r = 0.21; p = 0.045), total cholesterol (r = − 0.22; p = 0.037) and low-density lipoprotein cholesterol (r = − 0.22; p = 0.037). Only total cholesterol (β = − 4.41; p < 0.001) and estrogen (β = 2.25; p = 0.03) were significantly associated with number of AR CAG repeats in regression analysis. In conclusion, AR CAG repeat length did not show any significant correlation with IR or β-cell function. Positive association of AR CAG with systolic and diastolic blood pressure and negative association of AR CAG with total and low-density lipoprotein cholesterol deserves further attention.

Cross-sectional association between testosterone, sex hormone-binding globulin and metabolic syndrome: The Healthy Twin Study

OBJECTIVES

This study evaluated an association between testosterone, sex hormone-binding globulin (SHBG) and metabolic syndrome (MetS).We also evaluated the genetic and environmental influences on the association.

DESIGN

Cross-sectional.

SETTING

Community-based study.

PARTICIPANTS

A total of 1098 Korean adult men including 139 monozygotic twin pairs.

MAIN OUTCOME MEASURE

MetS was defined using the National Cholesterol Education Program-Third Adult Treatment Panel (NCEP ATP III) and International Diabetes Federation (IDF) criteria. The associations between MetS and sex hormones were evaluated using linear mixed model and generalized estimating equation model.

RESULTS

After considering covariates such as smoking, alcohol consumption and physical exercises as well as SHBG or testosterone, the risk of MetS defined by NCEP ATP III criteria decreased by 31%, 29%, and 48%, respectively, with 1-standard deviation increase in total testosterone (TT), free testosterone (cFT) and SHBG. Similar findings were revealed with IDF criteria. Metabolic component specific analysis showed that sex hormones were inversely associated with several components of MetS: TT with abdominal obesity, low high-density lipoprotein cholesterol (HDL-C) and high blood pressure; cFT with abdominal obesity and high blood pressure; SHBG with all components except high blood pressure. Cotwin control analysis found an inverse correlation between within-pair differences in testosterone and SHBG levels and within-pair differences in waist circumference only.

CONCLUSION

Both testosterone and SHBG were inversely associated with MetS although the inverse associations with the sex hormones were not consistently found across individual metabolic components. Findings from cotwin analysis suggest a significant contribution of unshared unique environmental effect to the association between testosterone and SHBG and abdominal obesity.

Testosterone and androgen receptor gene polymorphism are associated with confidence and competitiveness in men

A contribution to a special issue on Hormones and Human Competition. Studies in non-human animals and humans have demonstrated the important role of testosterone in competitive interactions. Here, we investigated whether endogenous testosterone levels predict the decision to compete, in a design excluding spite as a motive underlying competitiveness. In a laboratory experiment with real monetary incentives, 181 men solved arithmetic problems, first under a noncompetitive piece rate, followed by a competition incentive scheme. We also assessed several parameters relevant to competition, such as risk taking, performance, and confidence in one's own performance. Salivary testosterone levels were measured before and 20min after the competition task using mass spectrometry. Participants were also genotyped for the CAG repeat polymorphism of the androgen receptor gene, known to influence the efficacy of testosterone signaling in a reciprocal relationship to the number of CAG repeats. We observed a significant positive association between basal testosterone levels and the decision to compete, and that higher testosterone levels were related to greater confidence in one's own performance. Whereas the number of CAG repeats was not associated with the choice to compete, a lower number of CAG repeats was related to greater confidence in those who chose to compete, but this effect was attributable to the polymorphism's effect on actual performance. An increase in testosterone levels was observed following the experiment, and this increase varied with self-reported high-school math grades. We expand upon the latest research by documenting effects of the androgen system in confidence in one's own ability, and conclude that testosterone promotes competitiveness without spite.

Estrogens and Androgens in Skeletal Physiology and Pathophysiology

Estrogens and androgens influence the growth and maintenance of the mammalian skeleton and are responsible for its sexual dimorphism. Estrogen deficiency at menopause or loss of both estrogens and androgens in elderly men contribute to the development of osteoporosis, one of the most common and impactful metabolic diseases of old age. In the last 20 years, basic and clinical research advances, genetic insights from humans and rodents, and newer imaging technologies have changed considerably the landscape of our understanding of bone biology as well as the relationship between sex steroids and the physiology and pathophysiology of bone metabolism. Together with the appreciation of the side effects of estrogen-related therapies on breast cancer and cardiovascular diseases, these advances have also drastically altered the treatment of osteoporosis. In this article, we provide a comprehensive review of the molecular and cellular mechanisms of action of estrogens and androgens on bone, their influences on skeletal homeostasis during growth and adulthood, the pathogenetic mechanisms of the adverse effects of their deficiency on the female and male skeleton, as well as the role of natural and synthetic estrogenic or androgenic compounds in the pharmacotherapy of osteoporosis. We highlight latest advances on the crosstalk between hormonal and mechanical signals, the relevance of the antioxidant properties of estrogens and androgens, the difference of their cellular targets in different bone envelopes, the role of estrogen deficiency in male osteoporosis, and the contribution of estrogen or androgen deficiency to the monomorphic effects of aging on skeletal involution.

The androgen receptor gene CAG repeat in relation to 4-year changes in androgen-sensitive endpoints in community-dwelling older European men

CONTEXT

The androgen receptor (AR) gene exon 1 CAG repeat length has been proposed to be a determinant of between-individual variations in androgen action in target tissues, which might regulate phenotypic differences of human ageing. However, findings on its phenotypic effects are inconclusive.

OBJECTIVE

To assess whether the AR CAG repeat length is associated with longitudinal changes in endpoints that are influenced by testosterone (T) levels in middle-aged and elderly European men.

DESIGN

Multinational European observational prospective cohort study.

PARTICIPANTS

A total of 1887 men (mean ± s.d. age: 63 ± 11 years; median follow up: 4.3 years) from centres of eight European countries comprised the analysis sample after exclusion of those with diagnosed diseases of the hypothalamic-pituitary-testicular (HPT) axis.

MAIN OUTCOME MEASURES

Longitudinal associations between the AR CAG repeat and changes in androgen-sensitive endpoints (ASEs) and medical conditions were assessed using regression analysis adjusting for age and centre. The AR CAG repeat length was treated as both a continuous and a categorical (6-20; 21-23; 24-39 repeats) predictor. Additional analysis investigated whether results were independent of baseline T or oestradiol (E₂) levels.

RESULTS

The AR CAG repeat, when used as a continuous or a categorical predictor, was not associated with longitudinal changes in ASEs or medical conditions after adjustments. These results were independent of T and E₂ levels.

CONCLUSION

Within a 4-year time frame, variations in the AR CAG repeat do not contribute to the rate of phenotypic ageing, over and above, which might be associated with the age-related decline in T levels.

Androgen receptor CAG repeat polymorphism and hypothalamic-pituitary-gonadal function in Filipino young adult males

OBJECTIVES

Testosterone (T), the primary androgenic hormone in males, is stimulated through pulsatile secretion of LH and regulated through negative feedback inhibition at the hypothalamus and pituitary. The hypothalamic-pituitary-gonadal (HPG) axis also controls sperm production through the secretion of follicle-stimulating hormone (FSH). Negative feedback in the HPG axis is achieved in part through the binding of T to the androgen receptor (AR), which contains a highly variable trinucleotide repeat polymorphism (AR-CAGn). The number of repeats in the AR-CAGn inversely correlates with transcriptional activity of the AR. Thus, we predicted longer AR-CAGn to be associated with higher T, LH, and FSH levels.

METHODS

We examined the relationship between AR-CAGn and total plasma T, LH, and FSH, as well as "bioavailable" morning (AM-T) and evening (PM-T) testosterone in 722 young (21.5 ± 0.5 years) Filipino males.

RESULTS

There was no relationship between AR-CAGn and total T, AM-T, or LH (P > .25 for all). We did observe a marginally non-significant (P = .066) correlation between AR-CAGn and PM-T in the predicted direction, and a negative correlation between AR-CAGn and FSH (P = .005).

CONCLUSIONS

Our results both support and differ from previous findings in this area, and study parameters that differ between our study and others, such as participant age, sample time, and the role of other hormones should be considered when interpreting our findings. While our data point to a modest effect of AR-CAGn on HPG regulation at best, the AR-CAGn may still affect somatic traits by regulating androgenic activity at peripheral tissues.

Influence of CAG Repeat Polymorphism on the Targets of Testosterone Action

In the last decade, ample evidence has demonstrated the growing importance of androgen receptor (AR) CAG repeat polymorphism in andrology. This genetic parameter is able to condition the peripheral effects of testosterone and therefore to influence male sexual function and fertility, cardiovascular risk, body composition, bone metabolism, the risk of prostate and testicular cancer, the psychiatric status, and the onset of neurodegenerative disorders. In this review, we extensively discuss the literature data and identify a role for AR CAG repeat polymorphism in conditioning the systemic testosterone effects. In particular, our main purpose was to provide an updated text able to shed light on the many and often contradictory findings reporting an influence of CAG repeat polymorphism on the targets of testosterone action.

Relationships among androgen receptor CAG repeat polymorphism, sex hormones and penile length in Han adult men from China: a cross-sectional study

This study aimed to investigate the correlations among androgen receptor (AR) CAG repeat polymorphism, sex hormones and penile length in healthy Chinese young adult men. Two hundred and fifty-three healthy men (aged 22.8 ± 3.1 years) were enrolled. The individuals were grouped as CAG short (CAG_S) if they harbored repeat length of ≤20 or as CAG long (CAG_L) if their CAG repeat length was >20. Body height/weight, penile length and other parameters were examined and recorded by the specified physicians; CAG repeat polymorphism was determined by the polymerase chain reaction (PCR) method; and the serum levels of the sex hormones were detected by radioimmunoassay. Student's t-test or linear regression analysis was used to assess the associations among AR CAG repeat polymorphism, sex hormones and penile length. This investigation showed that the serum total testosterone (T) level was positively associated with the AR CAG repeat length (P = 0.01); whereas, no significant correlation of T or AR CAG repeat polymorphism with the penile length was found (P = 0.593). Interestingly, an inverse association was observed between serum prolactin (PRL) levels and penile length by linear regression analyses (β= −0.024, P = 0.039, 95% confidence interval (CI): −0.047, 0). Collectively, this study provides the first evidence that serum PRL, but not T or AR CAG repeat polymorphism, is correlated with penile length in the Han adult population from northwestern China.

Sex steroid actions in male bone

Sex steroids are chief regulators of gender differences in the skeleton, and male gender is one of the strongest protective factors against osteoporotic fractures. This advantage in bone strength relies mainly on greater cortical bone expansion during pubertal peak bone mass acquisition and superior skeletal maintenance during aging. During both these phases, estrogens acting via estrogen receptor-α in osteoblast lineage cells are crucial for male cortical and trabecular bone, as evident from conditional genetic mouse models, epidemiological studies, rare genetic conditions, genome-wide meta-analyses, and recent interventional trials. Genetic mouse models have also demonstrated a direct role for androgens independent of aromatization on trabecular bone via the androgen receptor in osteoblasts and osteocytes, although the target cell for their key effects on periosteal bone formation remains elusive. Low serum estradiol predicts incident fractures, but the highest risk occurs in men with additionally low T and high SHBG. Still, the possible clinical utility of serum sex steroids for fracture prediction is unknown. It is likely that sex steroid actions on male bone metabolism rely also on extraskeletal mechanisms and cross talk with other signaling pathways. We propose that estrogens influence fracture risk in aging men via direct effects on bone, whereas androgens exert an additional antifracture effect mainly via extraskeletal parameters such as muscle mass and propensity to fall. Given the demographic trends of increased longevity and consequent rise of osteoporosis, an increased understanding of how sex steroids influence male bone health remains a high research priority.

Effects of testosterone replacement therapy on bone metabolism in male post-surgical hypogonadotropic hypogonadism: focus on the role of androgen receptor CAG polymorphism

INTRODUCTION AND AIM

The relationship between androgen receptor (AR) CAG polymorphism and bone metabolism is highly controversial. We, therefore, aimed to evaluate the independent role of AR CAG repeat polymorphism on bone metabolism improvement induced by testosterone replacement therapy (TRT) in male post-surgical hypogonadotropic hypogonadism, a condition frequently associated with hypopituitarism and in which the effects of TRT have to be distinguished from those resulting from concomitant administration of pituitary function replacing hormones.

METHODS

12 men affected by post-surgical hypogonadotropic hypogonadism [mean duration of hypogonadism 8.3 ± 2.05 (SD) months] were retrospectively assessed before and after TRT (from 74 to 84 weeks after the beginning of therapy). The following measures were studied: parameters of bone metabolism [serum markers and bone mineral density (BMD)], pituitary dependent hormones and genetic analysis (AR CAG repeat number).

RESULTS

Total testosterone, estradiol, free T4 (FT4) and insulin-like growth factor-1 (IGF-1) increased between the two phases, while follicle stimulating hormone (FSH) decreased. While serum markers did not vary significantly between the two phases, BMD improved slightly but significantly in all the studied sites. The number of CAG triplets correlated negatively and significantly with all the variations (Δ-) of BMDs. Conversely, Δ-testosterone correlated positively and significantly with all studied Δ-BMDs, while Δ-FSH, Δ-estradiol, Δ-FT4, and Δ-IGF-1 did not correlate significantly with any of the Δ-BMDs. Multiple linear regression analysis, after correction for Δ-testosterone, showed that CAG repeat length was negatively and significantly associated with ∆-BMD of all measured sites.

CONCLUSIONS

Our data suggest that, in post-surgical male hypogonadotropic hypogonadism, shorter AR CAG tract is independently associated with greater TRT-induced improvement of BMD.

Genome-wide association studies on serum sex steroid levels

Even though the levels of circulating sex steroid hormones are to a large extent heritable, their genetic determinants are largely unknown. With the advent of genome-wide association studies (GWAS), much progress has been made and several genetic loci have been identified to be associated with serum levels of dehydroepiandrosterone sulfate, testosterone and sex hormone-binding globulin. The variants identified so far only explain a small amount of the overall heritability, but may help to elucidate the role of sex steroid hormones in common disorders such as hypogonadism, type 2 diabetes and hormone-sensitive cancers. This review provides an overview of the current state of knowledge of the genetic determinants of sex steroid hormones, with a focus on recent GWAS and brief directions for elucidating the remaining heritability.

The relation between sex hormone levels, the androgen receptor CAGn-polymorphism and depression and mortality in older men in a community study

BACKGROUND

Sex hormones levels and the androgen receptor CAGn polymorphism have been shown to be involved in depressed mood in aging men. But the few prior studies found inconsistent results on the role of both factors.

METHODS

186 male participants aged ≥65 years from the community based Memory and Morbidity in Augsburg Elderly (MEMO) Study underwent a physical examination, and a medical interview including two scales (Center for Epidemiologic Studies Depression Scale (CES-D); Activities of Daily Living Scale (ADL). Testosterone, SHBG and LH levels were measured and the androgen receptor CAGn polymorphism was genotyped. χ(2), Mann-Whitney U-test, Pearson's correlations and multivariable linear and logistic regression were used in the analysis.

RESULTS

Higher depressive scores were significantly associated with higher SHBG-levels (beta coefficient 0.25, p<0.001). SHBG alone explained 8% of variance of the CES-D depression score. Mortality at 10 years follow-up was predicted by higher SHBG levels, higher ADL-scores, older age, current smoking and the depression score at baseline. This model explained 35% of the variance of mortality. The number of CAG repeats was neither related to depression scores nor to mortality.

CONCLUSIONS

We found positive associations between SHBG levels and old age male depression as well as mortality. Whether SHBG has a testosterone independent effect in this context should be investigated further.

Testosterone levels and androgen receptor gene polymorphism predict specific symptoms of depression in young men

BACKGROUND

Testosterone (T) has been hypothesized to modulate the expression of depressive symptoms in men; however, support for this proposition is mixed.

OBJECTIVE

To investigate bioavailable T, measured from saliva, and androgen receptor gene (AR) polymorphism (the number of glutamine [CAG] repeats in exon 1 of AR) and their relation to discrete symptoms of depression in 150 men aged 17 to 27 years who varied in mood status from depressed to nondepressed.

METHODS

Participants completed the Center for Epidemiologic Studies Depression Scale and the Patient Health Questionnaire-9. Principal components analysis of the scales identified 5 factors: Negative Affect, Social/Evaluative, Cognitive, Sleep, and Appetite.

RESULTS

Across the sample as a whole, higher ratings on sleep symptoms of depression were predicted by lower T concentrations and shorter CAG lengths. The association between T, CAG length, and sleep symptoms was confirmed among the subgroup of men who reported moderate to severe depression. In this subgroup, CAG repeats and T concentrations also emerged as significant predictors of negative affect scores, with the number of CAG repeats making the primary contribution.

CONCLUSIONS

These findings suggest that androgens may influence specific symptoms of depression in men.

The relationship of testosterone and AR CAG repeat genotype with knee extensor muscle function of young and older men

The inter-relationship between muscle strength and serum testosterone is not fully understood, and may be confounded or influenced by age. The polymorphism of androgen receptor gene CAG number (AR CAGn) could also influence these variables. The study examined the relationship between total testosterone (TT), free testosterone (FT) and AR CAGn with the muscle strength of young (YM, 18-30 yrs, n=82) and older (OM, 60-70 yrs, n=101) Caucasian men. Knee extensor strength was measured isometrically and isokinetically, and thigh and whole-body lean mass of the OM was determined by DXA. TT and serum hormone binding globulin (SHBG) were assayed by ELISA and used to calculate FT. AR CAGn was determined using polymerase chain reaction and microchip electrophoresis. OM were weaker than YM (-20 to -29%, all P<0.001), and serum androgens were lower (TT, -13%; FT, -13%; both P<0.001). TT was unrelated to any strength measurement in YM or OM. In the OM only, FT had a weak positive association with all three strength measures (r(2)=4.1-9.3%, P<0.036) and both whole body and thigh lean mass (r(2)=6.1-8.6%; P<0.013). Muscle strength was unrelated to AR CAGn for either the YM or OM, or when data were collapsed across both age groups (age normalised strength). Lean mass in the older cohort was also independent of AR CAGn. In conclusion, FT, but not TT or AR CAGn, was positively associated with muscle strength, but only as values declined with age.

The impact of androgen receptor CAG repeat polymorphism on andropausal symptoms in different serum testosterone levels

INTRODUCTION

In addition to a depletion of androgen, attenuated action of androgen receptor (AR) might also contribute to andropausal symptoms.

AIM

To evaluate the interaction of AR cytosine adenine guanine (CAG) repeat polymorphism and serum testosterone levels and their effect on andropausal symptoms in aging Taiwanese men.

METHODS

From August 2007 to April 2008, a free health screening for men older than 40 years was conducted by a medical center in Kaohsiung City, Taiwan. All participants received physical examination, answered questionnaires to collect their demographic information and medical histories, completed the Androgen Deficiency in the Aging Male (ADAM) questionnaire, and provided 20-cm(3) whole blood samples for biochemical and genetic evaluation.

MAIN OUTCOME MEASURES

The ADAM questionnaire was used to evaluate andropausal symptoms. Serum albumin, total testosterone (TT), and sex hormone-binding globulin levels were measured. Free testosterone level was calculated. AR gene CAG repeat polymorphism was determined by direct sequencing.

RESULTS

Seven hundred two men with the mean age of 57.2 ± 6.5 years were included. There was no significant association between TT levels and the distribution of AR CAG repeat polymorphism. When TT levels were above 340 ng/dL, subjects with AR CAG repeat lengths ~25 showed significantly higher risk of developing andropausal symptoms, as compared with those with AR CAG repeat lengths ~22 (P = 0.006), but this was not observed when TT levels were 340 ng/dL or below. Age and number of comorbidities were also independent risk factors for andropausal symptoms.

CONCLUSION

In subjects with normal TT concentration, those with longer AR CAG repeat lengths have a higher risk of developing andropausal symptoms. Age and number of comorbidities can also influence the appearance of andropausal symptoms. In clinical practice, a multifactorial approach to evaluate andropausal symptoms and the interactions between those risk factors is suggested.

Androgen receptor CAG repeat size is associated with stress fracture risk: a pilot study

BACKGROUND

Stress fractures commonly affect military recruits during basic training. Several lines of evidence suggest genetic factors are involved in stress fracture predisposition. As gender steroid hormone levels and activity have been implicated in affecting bone strength, one of the candidate genes likely to be involved is the androgen receptor gene.

QUESTIONS/PURPOSES

We assessed the possible involvement of the androgen receptor gene in stress fracture predisposition in Israeli soldiers.

PATIENTS AND METHODS

Between January 2007 and December 2009, we collected clinical and imaging data from 454 Israeli soldiers referred for bone scans with clinical symptoms compatible with stress fractures: 171 soldiers (154 men, 17 women) (patients) with bone scan-proven stress fractures and 283 soldiers (242 men, 41 women) with normal bone scans (control subjects). All participants were genotyped for the length of the CAG (cytosine-adenine-guanine) repeat in exon 1 of the androgen receptor gene using PCR and subsequent fragment analysis on sequence analyzer.

RESULTS

The androgen receptor gene CAG repeat was ranged between six and 31 (mean ± SD, 20.6 ± 4.3) among patients and between 11 and 32 (mean ± SD, 20.0 ± 3.8) among control subjects. Smaller-sized (< 16) androgen receptor CAG repeats were more prevalent among control subjects (23%) than among patients (13%); the risk for having SFs was almost halved if the size of the repeat was shorter than 16 repeats.

CONCLUSIONS

The androgen receptor gene CAG repeat has a different allele distribution among Israeli soldiers with stress fractures than in control subjects. While our finding must be validated, it could be used for screening individuals at risk for stress fractures.

LEVEL OF EVIDENCE

Level II, prognostic study. See the Guidelines for Authors complete description of levels of evidence.

Sex hormone levels, genetic androgen receptor polymorphism, and anxiety in ≥50-year-old males

INTRODUCTION

While associations between somatic changes and sex hormone levels in aging men have been explored in many studies, the association of testosterone and estradiol with psychic symptoms other than depression and the role of the genetically determined CAG repeat (CAGn) polymorphism of the androgen receptor (AR) have received much less attention.

AIM

The purpose of this article is to investigate the associations between general anxiety, phobic anxiety and panic with sex hormone levels and the genetic androgen receptor polymorphism in aging males.

METHODS

This cross-sectional study of males aged ≥50 years included 120 consecutive patients of the Department of Psychosomatics and Psychotherapy, 76 consecutive patients of the Andrology Clinic, and 100 participants from the general population; all of them completed the Brief Symptom Inventory (BSI), the Aging Males' Symptoms (AMS) Scale, and the Patient Health Questionnaire (PHQ-9). Morning blood samples were analyzed for total and free testosterone, estradiol, sex hormone-binding globulin (SHBG), and the CAGn AR polymorphism. Psychosomatic patients also underwent psychiatric assessment.

MAIN OUTCOME MEASURES

Scores on the Anxiety subscales of the BSI and PHQ, Anxiety disorders according to International Classification of Diseases, 10th revision (ICD-10).

RESULTS

The two clinical samples had significantly longer CAGn of the AR and higher anxiety levels compared to the population sample. Anxiety scores were positively correlated with CAGn in psychosomatic patients and in andrological patients, in the latter also with estradiol levels, while the population sample showed no significant correlations between anxiety scores, CAGn and sex hormones. Anxiety cases according to BSI, PHQ, and ICD-10 had significantly longer CAGn of the AR when compared to the other participants, but there were no significant differences in testosterone or free testosterone levels.

CONCLUSIONS

Our results indicate that genetically determined long CAGn of the AR is an independent risk factor for higher anxiety, panic and phobic anxiety levels.

Length of the human androgen receptor glutamine tract determines androgen sensitivity in vivo

A well established functional polymorphism of the human androgen receptor (hAR) is the length of AR's N-terminal glutamine tract (Q-tract). This tract is encoded by a CAG trinucleotide repeat and varies from 8 to 33 codons in the healthy population. Q-tract length is inversely correlated with AR transcriptional activity in vitro, but whether endogenous androgen action is affected is not consistently supported by results of clinical and epidemiological studies. To test whether Q-tract length influences androgen sensitivity in vivo, we examined effects of controlled androgen exposure in "humanized" mice with hAR knock-in alleles bearing 12, 21 or 48 CAGs. Mature male mice were analyzed before or 2weeks after orchidectomy, with or without a subdermal dihydrotestosterone (DHT) implant to attain stable levels of this non-aromatizable androgen. The validity of this DHT clamp was demonstrated by similar serum levels of DHT and its two primary 3αDiol and 3βDiol metabolites, regardless of AR Q-tract length. Q-tract length was inversely related to DHT-induced suppression of castrate serum LH (p=0.005), as well as seminal vesicle (SV) weight (p=0.005) and prostate lobe weights (p<0.006). This confirms that the hAR Q-tract polymorphism mediates in vivo tissue androgen sensitivity by impacting negative hypothalamic feedback and trophic androgen effects on target organs. In this manner, AR Q-tract length variation may influence numerous aspects of male health, from virilization to fertility, as well as androgen-dependent diseases, such as prostate cancer.

The genetics of bone loss: challenges and prospects

CONTEXT

A strong genetic influence on bone mineral density has been long established, and modern genotyping technologies have generated a flurry of new discoveries about the genetic determinants of bone mineral density (BMD) measured at a single time point. However, much less is known about the genetics of age-related bone loss. Identifying bone loss-related genes may provide new routes for therapeutic intervention and osteoporosis prevention.

EVIDENCE ACQUISITION

A review of published peer-reviewed literature on the genetics of bone loss was performed. Relevant studies were summarized, most of which were drawn from the period 1990-2010.

EVIDENCE SYNTHESIS

Although bone loss is a challenging phenotype, available evidence supports a substantial genetic contribution. Some of the genes identified from recent genome-wide association studies of cross-sectional BMD are attractive candidate genes for bone loss, most notably genes in the nuclear factor κB and estrogen endocrine pathways. New insights into the biology of skeletal development and regulation of bone turnover have inspired new hypotheses about genetic regulation of bone loss and may provide new directions for identifying genes associated with bone loss.

CONCLUSIONS

Although recent genome-wide association and candidate gene studies have begun to identify genes that influence BMD, efforts to identify susceptibility genes specific for bone loss have proceeded more slowly. Nevertheless, clues are beginning to emerge on where to look, and as population studies accumulate, there is hope that important bone loss susceptibility genes will soon be identified.

Role of polymorphism of the androgen receptor gene andnon-random x chromosome inactivation in the pathogenesisof androgenic alopecia

The article presents data on molecular and genetic studies of mechanisms of development of androgenic alopecia as well as correlation between polymorphism of the androgen receptor gene by the CAG repeat length in exon 1 and androgen-dependent diseases including alopecia.

Aggression, digit ratio and variation in androgen receptor and monoamine oxidase a genes in men

Variation in prenatal exposure to androgens is thought to be responsible for some of the individual differences in aggressive behavior among adults. A putative indicator of prenatal testosterone exposure, 2D:4D (the index to ring finger length) ratios have shown a weak correlation with aggression. Variation in sensitivity of the androgen receptor, resulting from polymorphism in the AR gene, is also thought to influence the relative expression of sexually dimorphic traits within each sex, including aggressive behavior and 2D:4D. Here we examine variation in aggression, 2D:4D, and polymorphism in the AR and MAO-A genes in a sample of 188 men. We find no evidence of AR gene influence on right hand 2D:4D, and a weak trend towards more feminine-typical left hand 2D:4D in men with more sensitive androgen receptors. Men with more sensitive androgen receptors tended to score lower on many of the subscales of the Aggression Questionnaire and Indirect Aggression Questionnaire. We found no influence of MAO-A allele on either digit ratio or aggressive behavior. We conclude that more masculine-typical 2D:4D does not reflect greater sensitivity to testosterone through variation in this locus on the AR gene, and that AR alleles conferring greater sensitivity to testosterone are associated with lower, not higher propensity to aggression.

A large study of androgen receptor germline variants and their relation to sex hormone levels and prostate cancer risk. Results from the National Cancer Institute Breast and Prostate Cancer Cohort Consortium

BACKGROUND

Androgens are key regulators of prostate gland maintenance and prostate cancer growth, and androgen deprivation therapy has been the mainstay of treatment for advanced prostate cancer for many years. A long-standing hypothesis has been that inherited variation in the androgen receptor (AR) gene plays a role in prostate cancer initiation. However, studies to date have been inconclusive and often suffered from small sample sizes.

OBJECTIVE AND METHODS

We investigated the association of AR sequence variants with circulating sex hormone levels and prostate cancer risk in 6058 prostate cancer cases and 6725 controls of Caucasian origin within the Breast and Prostate Cancer Cohort Consortium. We genotyped a highly polymorphic CAG microsatellite in exon 1 and six haplotype tagging single nucleotide polymorphisms and tested each genetic variant for association with prostate cancer risk and with sex steroid levels.

RESULTS

We observed no association between AR genetic variants and prostate cancer risk. However, there was a strong association between longer CAG repeats and higher levels of testosterone (P = 4.73 x 10(-5)) and estradiol (P = 0.0002), although the amount of variance explained was small (0.4 and 0.7%, respectively).

CONCLUSIONS

This study is the largest to date investigating AR sequence variants, sex steroid levels, and prostate cancer risk. Although we observed no association between AR sequence variants and prostate cancer risk, our results support earlier findings of a relation between the number of CAG repeats and circulating levels of testosterone and estradiol.

Bone mass and the CAG and GGN androgen receptor polymorphisms in young men

Background

To determine whether androgen receptor (AR) CAG (polyglutamine) and GGN (polyglycine) polymorphisms influence bone mineral density (BMD), osteocalcin and free serum testosterone concentration in young men.

Methodology/Principal Findings

Whole body, lumbar spine and femoral bone mineral content (BMC) and BMD, Dual X-ray Absorptiometry (DXA), AR repeat polymorphisms (PCR), osteocalcin and free testosterone (ELISA) were determined in 282 healthy men (28.6±7.6 years). Individuals were grouped as CAG short (CAG_S) if harboring repeat lengths of ≤21 or CAG long (CAG_L) if CAG >21, and GGN was considered short (GGN_S) or long (GGN_L) if GGN ≤23 or >23. There was an inverse association between logarithm of CAG and GGN length and Ward's Triangle BMC (r = −0.15 and −0.15, P<0.05, age and height adjusted). No associations between CAG or GGN repeat length and regional BMC or BMD were observed after adjusting for age. Whole body and regional BMC and BMD values were similar in men harboring CAG_S, CAG_L, GGN_S or GGN_L AR repeat polymorphisms. Men harboring the combination CAG_L+GGN_L had 6.3 and 4.4% higher lumbar spine BMC and BMD than men with the haplotype CAG_S+GGN_S (both P<0.05). Femoral neck BMD was 4.8% higher in the CAG_S+GGN_S compared with the CAG_L+GGN_S men (P<0.05). CAG_S, CAG_L, GGN_S, GGN_L men had similar osteocalcin concentration as well as the four CAG-GGN haplotypes studied.

Conclusion

AR polymorphisms have an influence on BMC and BMD in healthy adult humans, which cannot be explained through effects in osteoblastic activity.

Frailty, serum androgens, and the CAG repeat polymorphism: results from the Massachusetts Male Aging Study

CONTEXT

The CAG repeat polymorphism in the androgen receptor, denoted (CAG)n, is thought to (inversely) index androgen sensitivity. We hypothesized that (CAG)n would exhibit a modifying influence on the association between circulating total and calculated free testosterone (TT and FT) and physical frailty in aging men.

OBJECTIVE

The objective of the study was to establish the influence of (CAG)n on the relation between circulating TT, FT, LH, SHBG, and frailty.

DESIGN

This was a prospective cohort study of health and endocrine functioning in randomly selected men, with a baseline (T1: 1987-89) and two follow-up (T2: 1995-1997; T3: 2002-2004) visits.

SETTING

This was an observational study of men residing in greater Boston, MA.

PARTICIPANTS

A total of 624 subjects aged 50-86 yr were retained.

MAIN OUTCOME MEASURES

The frailty phenotype was measured at T3. Components included weight loss, exhaustion, low physical activity, weakness, and slowness. Subjects exhibiting two of these five components were considered to be in an intermediate state, and those exhibiting three or more were considered frail.

RESULTS

(CAG)n was positively associated with TT and FT. Multivariable regression analyses revealed no influence of CAG on longitudinal within-subject changes in hormone levels or cross-sectional (T3) associations between hormone concentrations and the prevalence of intermediate frailty or frailty. Models incorporating subjects' history of hormone decline produced similar negative results.

CONCLUSIONS

This population-based study does not support the hypothesis that interindividual differences in (CAG)n can account for a lack of association between circulating androgens and the frailty phenotype. Longitudinal analyses are needed to confirm these conclusions.

The impact of the CAG repeat polymorphism of the androgen receptor gene on muscle and adipose tissues in 20-29-year-old Danish men: Odense Androgen Study

BACKGROUND

The number of CAG repeats (CAG(n)) within the CAG repeat polymorphism of the androgen receptor gene correlates inversely with the transactivation of the receptor.

OBJECTIVE

To examine the impact of CAG(n) on muscle, fat distribution, and circulating androgen levels. Design, settings and participants Population-based, cross-sectional study of 783 Danish men aged 20-29 years.

METHODS

Genotyping was performed in 767 men. Areas of thigh and lower trunk muscle (muscle(thigh) and muscle(lower trunk)), subcutaneous adipose tissues (SAT(thigh) and SAT(lower trunk)), and deep adipose tissues (i.m. and visceral) were measured in 393 men by magnetic resonance imaging (MRI). Lean body mass (LBM) and fat mass (FM) were measured in all men by whole body dual-energy X-ray absorptiometry (DEXA). The absolute areas acquired by MRI were the main outcomes. The absolute DEXA measurements and relative assessments of both modalities were considered as the secondary outcomes. Results CAG(n) (range: 10-32) correlated inversely with absolute muscle(thigh) (r=-0.108), absolute muscle(lower trunk) (r=-0.132), relative muscle(thigh) (r=-0.128), relative muscle(lower trunk) (r=-0.126), relative LBM(lower extremity) (r=-0.108), and relative LBM(total) (r=-0.082), and positively with relative SAT(thigh) (r=0.137), relative SAT(lower trunk) (r=0.188), relative FM(lower extremity) (r=0.107), and relative FM(total) (r=0.082). These relationships remained significant, controlling for physical activity, smoking, chronic disease, and age. CAG(n) did not correlate with any circulating androgen.

CONCLUSIONS

The CAG repeat polymorphism affects body composition in young men: absolute muscle(thigh) and absolute muscle(lower trunk) increase as CAG(n) decreases. Expressed relatively, muscle areas and LBM increase, while SAT and FM decrease as CAG(n) decreases. The polymorphism does not affect deep adipose tissues or circulating androgen levels in young men.

Androgen receptor CAG repeat length and risk of biliary tract cancer and stones

Biliary tract cancers, encompassing cancers of the gallbladder, extrahepatic bile ducts, and ampulla of Vater, are rare but highly fatal. Gallstones represent the major risk factor for biliary tract cancer, and share with gallbladder cancer a female predominance and an association with reproductive factors and obesity. Although estrogens have been implicated in earlier studies of gallbladder cancer, there are no data on the role of androgens. Because intracellular androgen activity is mediated through the androgen receptor (AR), we examined associations between AR CAG repeat length [(CAG)(n)] and the risk of biliary tract cancers and stones in a population-based study of 331 incident cancer cases, 837 gallstone cases, and 750 controls from Shanghai, China, where the incidence rates for biliary tract cancer are rising sharply. Men with (CAG)(n) >24 had a significant 2-fold risk of gallbladder cancer [odds ratio (OR), 2.00; 95% confidence interval (CI), 1.07-3.73], relative to those with (CAG)(n) < or = 22. In contrast, women with (CAG)(n) >24 had reduced gallbladder cancer risk (OR, 0.69; 95% CI, 0.43-1.09) relative to those with (CAG)(n) < or = 22; P interaction sex = 0.01, which was most pronounced for women ages 68 to 74 (OR, 0.48; 95% CI, 0.25-0.93; P interaction age = 0.02). No associations were found for bile duct cancer or gallstones. Reasons for the heterogeneity of genetic effects by gender and age are unclear but may reflect an interplay between AR and the levels of androgen as well as estrogen in men and older women. Further studies are needed to confirm these findings and clarify the mechanisms involved.

Salivary testosterone and a trinucleotide (CAG) length polymorphism in the androgen receptor gene predict amygdala reactivity in men

In studies employing functional magnetic resonance imaging (fMRI), reactivity of the amygdala to threat-related sensory cues (viz., facial displays of negative emotion) has been found to correlate positively with interindividual variability in testosterone levels of women and young men and to increase on acute administration of exogenous testosterone. Many of the biological actions of testosterone are mediated by intracellular androgen receptors (ARs), which exert transcriptional control of androgen-dependent genes and are expressed in various regions of the brain, including the amygdala. Transactivation potential of the AR decreases (yielding relative androgen insensitivity) with expansion a polyglutamine stretch in the N-terminal domain of the AR protein, as encoded by a trinucleotide (CAG) repeat polymorphism in exon 1 of the X-chromosome AR gene. Here we examined whether amygdala reactivity to threat-related facial expressions (fear, anger) differs as a function of AR CAG length variation and endogenous (salivary) testosterone in a mid-life sample of 41 healthy men (mean age=45.6 years, range: 34-54 years; CAG repeats, range: 19-29). Testosterone correlated inversely with participant age (r=-0.39, p=0.012) and positively with number of CAG repeats (r=0.45, p=0.003). In partial correlations adjusted for testosterone level, reactivity in the ventral amygdala was lowest among men with largest number of CAG repeats. This inverse association was seen in both the right (r(p)=-0.34, p<0.05) and left (r(p)=-0.32, p<0.05) hemisphere. Activation of dorsal amygdala, correlated positively with individual differences in salivary testosterone, also in right (r=0.40, p<0.02) and left (r=0.32, p<0.05) hemisphere, but was not affected by number of CAG repeats. Hence, androgenic influences on threat-related reactivity in the ventral amygdala may be moderated partially by CAG length variation in the AR gene. Because individual differences in salivary testosterone also predicted dorsal amygdala reactivity and did so independently of CAG repeats, it is suggested that androgenic influences within this anatomically distinct region may be mediated, in part, by non-genomic or AR-independent mechanisms.

Genetic variations in sex steroid-related genes as predictors of serum estrogen levels in men

CONTEXT

The risk of many conditions, including prostate cancer, breast cancer, and osteoporosis, is associated with serum levels of sex steroids.

OBJECTIVE

The aim of the study was to identify genetic variations in sex steroid-related genes that are associated with serum levels of estradiol (E2) and/or testosterone in men.

DESIGN

Genotyping of 604 single nucleotide polymorphisms in 50 sex steroid-related candidate genes was performed in the Gothenburg Osteoporosis and Obesity Determinants (GOOD) study (n = 1041 men; age, 18.9 +/- 0.6 yr). Replications of significant associations were performed in the Osteoporotic Fractures in Men (MrOS) Sweden study (n = 2568 men; age, 75.5 +/- 3.2 yr) and in the MrOS US study (n = 1922 men; age, 73.5 +/- 5.8 yr). Serum E2, testosterone, and estrone (E1) levels were analyzed using gas chromatography/mass spectrometry.

RESULTS

The screening in the GOOD cohort identified the single nucleotide polymorphism rs2470152 in intron 1 of the CYP19 gene, which codes for aromatase, responsible for the final step of the biosynthesis of E2 and E1, to be most significantly associated with serum E2 levels (P = 2 x 10(-6)). This association was confirmed both in the MrOS Sweden study (P = 9 x 10(-7)) and in the MrOS US study (P = 1 x 10(-4)). When analyzed in all subjects (n = 5531), rs2470152 was clearly associated with both E2 (P = 2 x 10(-14)) and E1 (P = 8 x 10(-19)) levels. In addition, this polymorphism was modestly associated with lumbar spine BMD (P < 0.01) and prevalent self-reported fractures (P < 0.05).

CONCLUSIONS

rs2470152 of the CYP19 gene is clearly associated with serum E2 and E1 levels in men.

Androgen receptor gene polymorphism and sex hormones in elderly men: the Tromsø study

The aim of this study was to examine whether CAG/GGN repeats are significant modulators of serum concentrations of total and free testosterone (T) as well as of luteinizing hormone (LH) in elderly men. Sixty-nine 60- to 80-year-old men with subnormal T levels (< or = 11.0 nmol L(-1)) and 104 men with normal T levels taking part in a nested case-control study were used for these analyses. Sex hormones were measured and free T was calculated. The CAG and GGN polymorphisms in the androgen receptor gene were determined by polymerase chain reaction and subsequent direct sequencing. There were no differences in the CAG and GGN repeat lengths between the groups. In cross-sectional analyses of the whole cohort, total and free T were positively associated with CAG length (all P < 0.05) before, but not after, waist circumference or body mass index was added to the model. CAG repeat lengths were weakly, but not independently, associated with total and free T. These findings indicate that when clinically evaluating T and LH levels in elderly men, the CAG and GGN repeat lengths do not need to be taken into consideration.

Increased estrogen rather than decreased androgen action is associated with longer androgen receptor CAG repeats

CONTEXT

The individual variability in the waning androgenic-anabolic functions of aging men may be influenced by the CAG repeat polymorphism in exon 1 of the androgen receptor (AR), affecting androgen sensitivity. However, findings on its phenotypic effects are inconclusive.

OBJECTIVE

The aim was to investigate the relationships between health status, various reproductive hormones, and the AR CAG repeat length.

DESIGN

We conducted a multinational prospective cohort observational study with cross-sectional baseline data.

SETTING

This was a population survey of community-dwelling men.

PARTICIPANTS

Men (40-79 yr old; n = 3369) were randomly recruited from centers in eight European countries; CAG repeat analysis was performed in 2878 men.

MAIN OUTCOME MEASURES

We measured the correlations of the CAG repeat length with selected endocrine, metabolic, and phenotypic parameters related to aging and sex hormone action.

RESULTS

Only minor differences were found in CAG repeat lengths between the eight European countries. They showed significant positive association with total, free, and bioavailable levels of testosterone (T) and estradiol. FSH but not LH correlated inversely with CAG repeat length. Significant associations were found with bone ultrasound parameters at the calcaneus. Negative correlation was found with triglycerides, but not with other blood lipids or with anthropometry, blood pressure, hemoglobin, insulin sensitivity, or sexual and prostatic functions.

CONCLUSIONS

The AR CAG repeat length correlates significantly with serum T and estradiol of aging men. Weaker transcriptional activity of the AR with longer CAG-encoded polyglutamine repeats appears to be totally or nearly totally compensated for by higher T levels. The residual phenotypic correlations may reflect differences in estrogen levels/actions after aromatization of the higher T levels.

Association between repeat length of exon 1 CAG microsatellite in the androgen receptor and bone density in men is modulated by sex hormone levels

In this study we examined whether the androgen receptor (AR) gene CAG repeat polymorphism and serum androgen levels are associated with bone mineral density (BMD) and changes in BMD during 2-3 years in 229 healthy men 41-76 years old. Microsatellite analysis was performed on an automated sequencer. Indices of bioavailable testosterone (free testosterone [FT] and free androgen index) were calculated. BMD was measured using both dual-energy Xray absorptiometry and quantitative ultrasound. All participants completed a questionnaire regarding major possible osteoporosis risk factors. In linear regression analysis there was a modest positive association, which was independent of age and body mass index (BMI), between AR repeat length and BMD at all sites. Although this association was significant independent of BMI, analyses in the subgroup of obese men (BMI > 30) did not reach significance, while the effect was enhanced when analyzing only nonobese men (BMI < or = 30). There was no association between the AR gene polymorphism and rate of bone loss, FT, and BMD or testosterone and bone loss. Interestingly, the association between AR and BMD was modified by total testosterone. The lowest age- and BMI-adjusted average femoral neck BMD was found among men in the lowest tertile for both AR repeat length and FT, whereas men within the higher categories of these variables displayed the highest BMD. In conclusion, there is a positive association between the AR CAG repeat polymorphism and BMD, which is modified by androgen levels in healthy men.

Contribution of gender-specific genetic factors to osteoporosis risk

Common diseases result from the complex relationship between genetic and environmental factors. The aim of this review is to provide perspective for a conceptual framework aimed at studying the interplay of gender-specific genetic and environmental factors in the etiology of complex disease, using osteoporosis as an example. In recent years, gender differences in the heritability of the osteoporosis-related phenotypes have been reported and sex-specific quantitative-trait loci were discovered by linkage studies in humans and mice. Results of numerous allelic association studies also differed by gender. In most cases, it was not clear whether or not this phenomenon should be attributed to the effect of sex-chromosomes, sex hormones, or other intrinsic or extrinsic differences between the genders, such as the level of bioavailable estrogen and of physical activity. We conclude that there is need to consider gender-specific genetic and environmental factors in the planning of future association studies on the etiology of osteoporosis and other complex diseases prevalent in the general population.

Part of the interindividual variation in serum testosterone levels in healthy men reflects differences in androgen sensitivity and feedback set point: contribution of the androgen receptor polyglutamine tract polymorphism

CONTEXT

There is a large interindividual variation in serum (free) testosterone (FT) levels in men, underlain in part by genetic components.

OBJECTIVE

The objective of the study was to explore the hypothesis that this variability results in part from differences in androgen sensitivity and feedback loop set point and assess the role of the androgen receptor (AR) polyglutamine tract polymorphism encoded by a CAG repeat of variable length in exon 1 of the AR gene.

DESIGN/SETTING/PARTICIPANTS

We performed a cross-sectional analysis in two independent populations of healthy men, consisting of 2322 men aged 35-59 yr (Belstress study) and 358 men aged 25-45 yr (Siblos study), respectively.

MAIN OUTCOME MEASURES

Serum hormonal levels and the AR gene CAG repeat length were determined.

RESULTS

In the Belstress population, serum testosterone and calculated FT showed a positive linear association with LH (P < 0.001). In the 200 men with lowest FT, CAG repeat number was lower than in the 200 men with highest FT (P = 0.004). As studied in a larger subset of the population consisting of 857 men covering the whole FT range, FT increased progressively with CAG repeat length (P = 0.003). These findings of a positive relation of FT with both LH and CAG repeat length were confirmed in the Siblos study population (both P < or = 0.001). Difference in FT between extreme quartiles of CAG repeat was 10 and 14% in the Belstress and Siblos study, respectively. In both study populations, CAG repeat length was also positively associated with serum total testosterone (P < or = 0.004).

CONCLUSIONS

The data support the view that between-subject variability in serum FT in healthy men is underlain in part by differences in androgen sensitivity and feedback set point, with a contributory role of AR polymorphism. These findings have potential implications for the interpretation of epidemiological studies, diagnosis of hypogonadism, and pharmacogenetics of androgen treatment in men.

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.

Genetic and constitutional influences on bone turnover markers: a study of male twin pairs

Biochemical markers of bone turnover originating from type I procollagen synthesis or type I collagen breakdown were examined in men using a classic twin study design based on monozygotic (MZ) and dizygotic (DZ) twins. The aim was to estimate the influence of heredity (genes and shared family childhood elements) and constitutional factors in determining procollagen type I amino-terminal propeptide (PINP), type I collagen carboxy-terminal telopeptide (ICTP), and urinary amino-terminal type I collagen telopeptide (NTx) marker levels in a sample of in 98 MZ and 108 DZ male twin pairs. We are not aware of any prior studies conducted in men that address the influence of genetic factors on bone turnover marker variability. The findings support a dominant role for heredity in the variation of bone resorption marker levels in men, with additive genetic effects explaining two-thirds of the variance in the bone resorption markers NTx and ICTP. Genetic factors may contribute less for PINP, a marker of bone formation. The genetic loci influencing PINP or NTx and body weight/disc axial area, although related in part, appeared to be largely independent, indicating that genetic effects on bone turnover are unlikely to be to a large degree a result of genetic regulation of individual body weight.

Association between androgen receptor gene polymorphism and bone density in older women using hormone replacement therapy

OBJECTIVE

The objective of this study was to investigate the relationship between bone mineral density (BMD) and both CAG repeat polymorphism of the androgen receptor (AR) gene and skewed X chromosome inactivation (SI) in postmenopausal women.

METHODS

BMD was measured by DEXA. Both the number and the X-weighted biallelic mean of the CAG repeats of AR were analysed by PCR, before and after DNA digestion with methylation-sensitive HpaII in 192 healthy Caucasian postmenopausal women.

RESULTS

The number of CAG repeats ranged from 10 to 34, with a median value of 22. CAG)(n< or =22) and CAG)(n> or =23) alleles were designated as short and long alleles, respectively. In women using hormone replacement therapy (HRT) (n=81), lumbar spine BMD was significantly lower, and femoral neck and total body BMD marginally lower in those with long-long alleles when compared with those with other genotypes. SI (> or =80%) was observed in 24% of the women and was not associated with BMD. In women using HRT, femoral neck BMD was significantly lower, and lumbar spine and total body BMD marginally lower in those whose X-weighted CAG repeat biallelic was greater than 22.59 (median value) when compared to other genotypes. These results were not found in women not using HRT.

CONCLUSION

In conclusion, our results suggest that BMD may be associated with AR gene polymorphism in postmenopausal women using HRT but not with SI. Further studies are needed to investigate the mechanisms of the interaction between HRT, BMD and AR found in the present study.

Association between androgen receptor gene CAG trinucleotide repeat length and testicular histology in older men

OBJECTIVE

To determine whether the size of CAG repeat in exon 1 of the androgen receptor (AR) gene is related to impaired spermatogenesis in older men.

DESIGN

Study of two groups of older men: one with preserved spermatogenesis and the other with arrested spermatogenesis.

SETTING

University teaching hospital.

PATIENT(S)

Twenty-eight men aged from 53 to 102 years.

INTERVENTION(S)

The DNA fragment encoding the AR polyglutamine tract was amplified from DNA of testis tissue.

MAIN OUTCOME MEASURE(S)

The size of the CAG repeat was evaluated by using fluorescent-labeled polymerase chain reaction performed on an ABI Prism 377 DNA sequencer followed by automated analysis with Genscan 3.1.2 software.

RESULT(S)

Mean CAG repeat length was 22.76 +/- 3 in the group of 13 aged men with preserved spermatogenesis and 21.86 +/- 2.23 in the group of 15 aged men with arrested spermatogenesis.

CONCLUSION(S)

Impaired spermatogenesis in elderly men does not seem to be correlated with the AR gene CAG repeat length, which therefore does not appear to be a risk factor for impaired spermatogenesis in older men.

The androgen receptor gene CAG repeat polymorphism does not predict increased risk of heart disease: longitudinal results from the Massachusetts Male Ageing Study

OBJECTIVE

Sex steroids may contribute to the increased prevalence of heart disease (HD) in men compared to age-matched women. Androgens bind their cognate receptor, and androgen action is inversely proportional to the number of CAG repeats in exon 1 of the androgen receptor gene. Longer, less androgenic CAG repeats have been associated with higher high-density lipoprotein (HDL) levels, which might protect against HD. Therefore, we hypothesized that CAG repeat length contributes to HD risk in men.

DESIGN

Longitudinal, population-based cohort study.

POPULATION

One thousand thirty-four participants from the Massachusetts Male Ageing Study, a cohort of 1709 men from the Boston area, aged 40-70, observed at three time points over 15 years.

METHODS

Poisson regression.

MEASUREMENTS

Heart disease was determined by self-report, medical records or from the National Death Index. Lipids and hormones were measured from blood samples drawn at each time point. CAG repeat length was assessed from DNA collected at the second time point.

RESULTS

We found no increased risk of HD associated with CAG repeat length in our analyses. Moreover, CAG repeat length was not related to body mass index, HDL, low-density lipoprotein or waist to hip ratio in this cohort; nor did CAG repeat length predict changes in these variables over 15 years of follow-up.

CONCLUSIONS

In contrast to previous smaller, cross-sectional analyses, in this large cohort of community-dwelling men followed over 15 years, CAG repeat length was not related to the incidence or prevalence of HD or alterations in HDL. If androgens impact HD risk, this effect is unlikely to be mediated via CAG repeat length.

The relation of the XbaI and PvuII polymorphisms of the estrogen receptor gene and the CAG repeat polymorphism of the androgen receptor gene to peak bone mass and bone turnover rate among young healthy men

The genes coding for estrogen receptor-alpha (ER-alpha) and androgen receptors (AR) are potential candidates for the regulation of bone mass and turnover, which may contribute to both the achievement of peak bone mass and bone loss after completion of growth. The present study was aimed at elucidating the role of two restriction fragment lengths (XbaI and PvuII) polymorphisms of the ER gene and the CAG repeat polymorphism of the AR gene as determinants of peak bone mass in men; special attention was paid to the interaction between serum free estradiol (E2) levels and the XbaI and PvuII genotypes. A cross-sectional study, with data on lifestyle factors collected retrospectively, was performed in 234 young men, aged 18.3 to 20.6 years. Of the men, 184 were recruits of the Finnish Army and 50 were men of similar age who had postponed their military service for reasons not related to health. Bone mineral content (BMC), density (BMD) and scan area were measured in the lumbar spine and upper femur by dual-energy X-ray absorptiometry (DXA). The bone turnover rate was assessed by measuring serum type I procollagen aminoterminal propeptide (PINP) and tartrate-resistant acid phosphatase 5b (TRACP5b) as well as urinary excretion of type I collagen aminoterminal telopeptide (NTX). After adjusting for age, height, weight, exercise, smoking, calcium and alcohol intake, BMC, scan area and BMD at all measurement sites were similar for the different XbaI and PvuII genotypes of the ER and independent of the number of the CAG repeats of the AR gene. No association was found between free E2 levels and bone parameters among any genotype group of the XbaI and PvuII polymorphisms. Except for urinary NTX, which showed a tendency to higher values for the xx (P=0.08) and pp (P=0.10) genotypes of the ER, bone turnover markers were not related to the genotypes studied. Our study does not support the view that the XbaI and PvuII polymorphisms of the ER gene and the CAG polymorphism of the AR gene would have a substantial impact on the development of peak bone mass in young Finnish men.

The decline of androgen levels in elderly men and its clinical and therapeutic implications

Aging in men is accompanied by a progressive, but individually variable decline of serum testosterone production, more than 20% of healthy men over 60 yr of age presenting with serum levels below the range for young men. Albeit the clinical picture of aging in men is reminiscent of that of hypogonadism in young men and decreased testosterone production appears to play a role in part of these clinical changes in at least some elderly men, the clinical relevancy of the age-related decline in sex steroid levels in men has not been unequivocally established. In fact, minimal androgen requirements for elderly men remain poorly defined and are likely to vary between individuals. Consequently, borderline androgen deficiency cannot be reliably diagnosed in the elderly, and strict differentiation between "substitutive" and "pharmacological" androgen administration is not possible. To date, only a few hundred elderly men have received androgen therapy in the setting of a randomized, controlled study, and many of these men were not androgen deficient. Most consistent effects of treatment have been on body composition, but to date there is no evidence-based documentation of clinical benefits of androgen administration to elderly men with normal or moderately low serum testosterone in terms of diminished morbidity or of improved survival or quality of life. Until the long-term risk-benefit ratio for androgen administration to elderly is established in adequately powered trials of longer duration, androgen administration to elderly men should be reserved for the minority of elderly men who have both clear clinical symptoms of hypogonadism and frankly low serum testosterone levels.

Androgen receptor polymorphism (CAG repeats) and androgenicity

Objective Polymorphism of the androgen receptor (AR) has been related to various pathophysiological conditions, such as osteoporosis and infertility. The objectives of this study were to evaluate the frequency of distribution in a normal Italian population and to assess CAG repeats (CAGr) in other conditions, such as hypoandrogenism, potentially influenced by AR polymorphism. Patients and measurements CAGr polymorphism was determined in a group of 91 healthy normoandrogenized subjects, 29 hypoandrogenized patients (hypoplasia of prostate and seminal vesicles, reduced beard or body hair, etc.) and 29 infertile patients by direct sequencing. Results The mean (+/- SD) number of CAG repeats [(CAGr)n] was 21.5 (+/- 1.7) in the control group, 21.4 (+/- 2.0) in the infertile patients and 24.0 (+/- 2.9) in the hypoandrogenic males. The difference was statistically significant between this last group and the other two (P < 0.0001), while there was no difference between normal controls and infertile patients. The frequency distribution showed a shift towards higher CAG length in hypoandrogenized patients compared to controls and infertile patients. If we used a cut-off point of 24.9 (2 SD above the mean), the percentage of patients with 25 or more CAGr repeats was 38% among hypoandrogenized patients, 7% among infertile patients and 5% among the control group. In hypoandrogenized subjects (CAGr)n correlated slightly with testis and prostate volume. The number of CAG repeats was not associated with any of the hormonal parameters, including testosterone, evaluated in the three groups. Conclusions Our normal population, representing subjects from Central Italy, is superimposable on other European populations with regard to (CAGr)n distribution. Hypoandrogenic males have a shift in the frequency distribution towards longer (CAGr)n. Infertile patients are not statistically different from the control group. These findings suggest that, given the same amount of circulating testosterone, as in our hypoandrogenized and control group, the final net androgenic phenotypical effect is due to AR polymorphism.

Association between androgen receptor gene CAG repeat polymorphism and plasma testosterone levels in postmenopausal women

OBJECTIVES

The biologic action of androgens in target cells depends on plasma androgen levels and receptor transcriptional activity. We investigated the relationship between androgen receptor (AR) CAG repeat polymorphism, serum androgen levels, and anthropometric, metabolic, and hormonal variables in 39 postmenopausal women, taking into consideration the patterns of X-chromosome inactivation.

METHODS

Genomic DNA was extracted from peripheral leukocytes. Polymerase chain reactions (PCRs) were performed to amplify the polymorphic (CAG)n repeat of the human AR gene, which were analyzed with GeneScan software (Applied Biosystems, Foster City, CA). The X-chromosome inactivation analysis was based on the AR gene methylation patterns.

RESULTS

The mean age of participants was 54.7 years; mean age at menopause was 48 years. The number of CAG repeats ranged from 15 to 30, with a median length of 23. Analysis of X-chromosome inactivation patterns showed 19 cases with a degree of skewing (DS) > or =70% and seven with a DS > or =90%. The X-weighted CAG repeat biallelic mean was significantly lower in individuals with total testosterone (TT) greater than 0.56 ng/mL (group mean) than in the group with TT < or =0.56 (P=.018). No difference was observed between the groups regarding dehydroepiandrosterone sulfate (DHEA-S). Plasma TT was significantly higher in the group with the smaller X-weighted CAG repeat biallelic mean (P=.01). Free androgen index (FAI) was also significantly higher in this group (P=.033). Testosterone levels and FAI were inversely correlated to X-weighted CAG repeat biallelic mean.

CONCLUSION

Our data indicate an association between testosterone plasma levels and AR CAG repeats in postmenopausal women, and suggest that plasma levels of androgens in postmenopausal women may be related to variants of the AR gene.