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

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.

Influence of estrogen receptor α polymorphisms on bone density in response to habitual exercise in Japanese postmenopausal women

Estrogen receptor α (ER α) is one of candidate genes for osteoporosis. This study examined the influence of ER α gene, PvuII, and XbaI genotypes on bone density of calcaneus in response to habitual exercise. ER α polymorphisms were detected using PvuII and XbaI restriction enzymes in 316 Japanese postmenopausal women. The bone density was significantly lower in the women carrying PP, pp, or xx genotype without habitual exercise than in the age-matched women without those genotypes. The women carrying Pp genotype without habitual exercise had normal bone density compared to those without Pp genotype. The women carrying PPxx or ppxx polymorphism without habitual exercise had low bone density compared to those with habitual exercise. Thus, the reduction of bone density was attenuated in the women carrying PPxx or ppxx with habitual exercise. In addition, habitual exercise was highly effective for the bone density in the women carrying xx homozygote. These findings indicate that analyses of XbaI and PvuII polymorphisms of ER α may be useful to predict the effect of exercise on bone density, and habitual exercise attenuates the reduction of bone density in women with some genotypes.

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.

Association of estrogen receptor α gene PvuII and XbaI polymorphisms with non-small cell lung cancer

Single nucleotide polymorphisms (SNPs) of the estrogen receptor (ER)-α have been found to be associated with various diseases at significantly different frequencies. However, whether any relationship exists between ER-α polymorphisms and lung cancer remains to be determined. In this study, 84 non-smoking, female, non-small cell lung cancer patients with various stages of disease and 234 cancer-free reference controls were enrolled to examine the association of ER-α polymorphisms in lung cancer. Two restriction SNP sites, PvuII and XbaI, in the first intron of the ER-α gene were genotyped by polymerase chain reaction-restriction fragment length polymorphism. The frequencies of the PvuII-XbaI haplotypes and genotypes in a Taiwanese population were revealed for the first time. Although the genotypic frequencies of two polymorphic sites of ER- α were in linkage disequilibrium for the lung cancer group (χ(2)=50.013, d.f.=4) and reference controls (χ(2)=60.797, d.f.=4); and 7 and 8 combined genotypes were present, respectively, the distribution and the major genotypes are different in the two groups (p<0.0001). The p-values for PvuII and XbaI genotypes were significantly different between the lung cancer and reference controls. The PP genotype presence was found to be significantly lower in the lung cancer group (P=0.005), whereas presence of the xx genotype was significantly higher (P=0.042). These findings suggested that the PP genotype had a lower risk of lung cancer; whereas the xx genotype had a higher risk. In comparison with other studies conducted in various populations, it is of note that the pX haplotype frequency of this study was higher than that of other studies, whereas the px haplotype was lower. Moreover, the Xx genotypic frequency of XbaI polymorphisms in the ER-α gene of the reference control group was found to be extremely high, whereas the xx genotypic frequency was extremely low. In conclusion, PvuII-XbaI polymorphisms of the ER-α gene were found to be associated with the risk, but not cancer severity, of non-small cell lung cancer in a Taiwanese population.

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.

Possible association of combined vitamin D receptor and estrogen receptor genotypes and low bone mineral density in Jordanian postmenopausal women

The genetics of osteoporosis has been extensively studied over the last 20 years. Many of the studies have been aimed at identifying possible risk factors and possible association with low bone mineral density (BMD). Vitamin D receptor (VDR) and estrogen receptor (ER) gene polymorphisms were the first to be studied. Some studies have shown a possible association for individual VDR and ER or combined VDR and ER genotypes in some populations, and others showed lack of such an association. This study is aiming at identification of a possible association with low BMD in Jordanian postmenopausal women. We used restriction fragment length polymorphisms (RFLPs) to study four polymorphisms in the VDR gene and two polymorphisms in the ER gene. Our sample was composed of 100 normal controls and 120 samples from patients with symptomatic vertebral fractures. The results showed a possible association of the ppxx genotype with low BMD in controls and patients and an association of the AaBbTT genotype with high BMD in control subjects. The AABBTT, AABBTTFF, and AABBTTFFPPXX genotypes showed a possible association with low BMD in patients. Further studies are needed to confirm the last finding since it could be an important predictor of low BMD in the Jordanian population.

Association between VDR and ESR1 gene polymorphisms with bone and obesity phenotypes in Chinese male nuclear families

AIM

The goal of this study was to determine whether polymorphisms in the vitamin D receptor (VDR) and estrogen receptor alpha (ESR1) genes are associated with variations of peak bone mineral density (BMD) and obesity phenotypes in young Chinese men.

METHODS

A total of 1215 subjects from 400 Chinese nuclear families were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and allele-specific multiple PCR (ASM-PCR) analysis at the ApaI, FokI, and CDX2 sites in the VDR gene and the PvuII and XbaI sites in the ESR1 gene. BMD at the lumbar spine and hip, total fat mass, and total lean mass were measured using dual energy X-ray absorptiometry. The associations between VDR and ESR1 gene polymorphisms with peak BMD, body mass index (BMI), total fat mass, total lean mass, and percentage fat mass (PFM) were determined using quantitative transmission disequilibrium tests (QTDTs).

RESULTS

Using QTDTs, no significant within-family associations were obtained between genotypes or haplotypes of the VDR and ESR1 genes and peak BMD. For the obesity phenotypes, the within-family associations were significant between CDX2 genotypes and BMI (P=0.046), fat mass (P=0.004), and PFM (P=0.020). Further, PvuII was significantly associated with the variation of fat mass and PFM (P=0.002 and P=0.039, respectively). A subsequent 1000 permutations were in agreement with these within-family association results.

CONCLUSION

Our findings showed that VDR and ESR1 polymorphisms were associated with total fat mass in young Chinese men, but we failed to find a significant association between VDR and ESR1 genotypes and peak BMD. These findings suggested that the VDR and ESR1 genes are quantitative trait loci (QTL) underlying fat mass variation in young Chinese men.

Molecular genetic studies of gene identification for osteoporosis

This review comprehensively summarizes the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of September 2007. It is intended to constitute a sequential update of our previously published reviews covering the available data up to the end of 2004. Evidence from candidate gene-association studies, genome-wide linkage and association studies, as well as functional genomic studies (including gene-expression microarray and proteomics) on osteogenesis and osteoporosis, are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. The major results of all studies are tabulated for comparison and ease of reference. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Relationship of volumetric bone mineral density and structural parameters with ERalpha gene polymorphisms

Bone mineral density (BMD) contributes to bone strength, and methods for clinical assessment of bone quality characteristics beyond what can be gathered by BMD are awaited. Peripheral quantitative computed tomography (pQCT) allows for separate assessments of cortical and trabecular bone, providing information on bone geometry. Previous studies examining the relationship between estrogen receptor alpha (ERalpha) gene polymorphisms and BMD have been performed in large populations. However, only limited information is available on the possible segregation of ERalpha gene polymorphisms with bone structural properties. The aim of our study was to evaluate the association of XbaI and PvuII ERalpha gene polymorphisms with QCT parameters. We studied 900 subjects (541 women, 449 men) participating to the InCHIANTI study. By tibial pQCT we evaluated trabecular volumetric BMD, cortical volumetric BMD, cortical bone area, and cortical thickness (CtTh). Subjects were genotyped for ERalpha gene PvuII and XbaI polymorphisms. Analysis of variance was used for statistical analysis. Male subjects with PP and XX genotypes had higher geometric parameters, and female subjects with XX and PP genotypes showed higher densitometric parameters than other genotypes; however, the differences did not reach statistical significance. After adjustment for potential confounders, we found a significant (P = 0.002) CtTh difference across PvuII polymorphism in male subjects, with higher CtTh values in PP genotypes with respect to Pp and pp genotypes. These results show a relationship between the presence of the P allele and higher values of CtTh in male subjects, indicating for ERalpha a role in the control of tibial bone geometry.

The A1330V polymorphism of the low-density lipoprotein receptor-related protein 5 gene (LRP5) associates with low peak bone mass in young healthy men

INTRODUCTION

Polymorphisms in the gene coding for low-density lipoprotein receptor-related protein 5 (LRP5) contribute to variation in bone mass in the general population. Whether this is due to influence on bone mass acquisition or on bone loss thereafter has not been established.

METHODS

We studied the association of LRP5 polymorphisms with peak bone mass in young men. The study included 235 Finnish men, aged 18.3 to 20.6 years. Lifestyle factors and fracture history were recorded. Bone mineral content (BMC), density (BMD) and scan area were measured for the lumbar spine and proximal femur by dual energy X-ray absorptiometry (DXA). Blood and urine were collected for determination of bone turnover markers, serum 25-OHD and PTH. Genomic DNA was extracted from peripheral blood for genetic analysis of LRP5. Ten single nucleotide polymorphisms in LRP5 were analyzed and correlated with bone parameters.

RESULTS

Only the A1330V polymorphism of LRP5 significantly associated with bone parameters. In comparison with subjects with the AlaAla genotype (n=215), those with AlaVal genotype (n=20) had lower femoral neck BMC (P=0.029) and BMD (P=0.012), trochanter BMC (P=0.0067) and BMD (P=0.015), and total hip BMC (P=0.0044) and BMD (P=0.0089). Fracture history was similar for the genotypes.

CONCLUSION

The polymorphic valine variant at position 1330 of LRP5 was significantly associated with reduced BMC and BMD values in healthy young Finnish men. The results provide evidence for the crucial role of LRP5 in peak bone mass acquisition.

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.

Quantitative ultrasound variables of the heel in Finnish men aged 18-20 yr: predictors, relationship to bone mineral content, and changes during military service

INTRODUCTION

Determinants of BUA and SOS and their changes during military service-associated physical training were studied in 196 army recruits and 50 control men, aged 18-20 years.

METHODS

Heel ultrasound measurement, DXA, muscle strength test, Cooper's running test and genetic analyses were performed. Lifestyle factors were recorded. Sex steroids and bone turnover markers were determined. Heel ultrasound was repeated after six months.

RESULTS

Exercise was the most significant determinant of both BUA (p<0.0001) and SOS (p<0.0001). There were 10% and 1.3% differences in BUA (p=0.006) and SOS (p=0.0001), respectively, between men belonging to the lowest and highest quartiles of exercise index. Weight associated with BUA (p=0.005) and height with SOS (p=0.03). BUA and SOS correlated with BMC and BMD (p<0.0001) but explained only up to 21% of their variance. Over six months SOS increased more in recruits than in control men (p=0.0043), the increase being higher, the lower muscle strength at baseline (r =-0.27, p=0.0028).

CONCLUSION

Exercise is the most important determinant of ultrasonographic variables in men, aged 18-20 years. Physical loading during military training increases SOS.

Molecular genetic studies of gene identification for osteoporosis: a 2004 update

This review summarizes comprehensively the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of December 2004. It is intended to constitute a sequential update of our previously published review covering the available data up to the end of 2002. Evidence from candidate gene association studies and genome-wide linkage studies in humans, as well as quantitative trait locus mapping animal models are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. An important extension of this update is incorporation of functional genomic studies (including DNA microarrays and proteomics) on osteogenesis and osteoporosis, in light of the rapid advances and the promising prospects of the field. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Association of repeat polymorphisms in the estrogen receptors alpha, beta, and androgen receptor genes with knee osteoarthritis

Genetic factors have been shown to play an important role in the etiology of osteoarthritis (OA). To elucidate the possible role of genetic variation in the estrogen receptors alpha and beta (ER-alpha, ER-beta) and androgen receptor (AR) genes with knee OA, the -1174(TA)(n), c.1092+3607(CA)(n), and c.172(CAG)(n) repeat polymorphisms of ER-alpha, ER-beta, and AR genes were studied. A case-control cohort of 158 patients with idiopathic knee OA and 193 controls were used. A significant difference was observed in the frequency distribution of -1174(TA)(9-25) and c.1092+3607(CA)(13-27) repeat polymorphisms of the ER-alpha and ER-beta genes between OA patients and controls (p<0.005 and p<0.0001, respectively). A significantly increased odds ratio (OR) for knee OA was observed in individuals having long alleles (LL) genotype for ER-alpha gene and LL and one short and one long allele (SL) genotypes for ER-beta gene compared to individuals with the short alleles (SS) genotype (95% CI 1.03-3.5; p=0.04 and CI 2.4-8.3 and 2.5-7.5; p < 0.001, respectively). When ORs were adjusted for various risk factors, it was observed that women with LL genotypes for ER-beta and AR genes showed significantly increased risk for OA development (p=0.002 and 0.001). An association between c.1092+3607(CA)(13-27) and c.172(CAG)(8-34) repeat polymorphisms of the ER-beta and AR genes and knee OA was found in individuals of Greek descent.

Risk factors for clinical stress fractures in male military recruits: a prospective cohort study

This prospective study was aimed at evaluating risk factors for symptomatic stress fractures among 179 Finnish male military recruits, aged 18 to 20 years. The subjects were studied in the very beginning of the military service of 6 to 12 months in summer. Bone mineral content (BMC) and density (BMD) were measured by dual energy X-ray absorptiometry (DXA) at the lumbar spine and at the hip and heel ultrasound investigation was performed. Blood was sampled for determination of serum total and free testosterone, total and free estradiol, sex hormone-binding globulin (SHBG), procollagen type I N propeptide, total and carboxylated osteocalcin, tartrate-resistant acid phosphatase 5b, 25-hydroxyvitamin D (25-OHD), and intact parathyroid hormone (iPTH), as well as for studying the XbaI and PvuII polymorphisms of the estrogen receptor gene and the CAG repeat polymorphism of the androgen receptor gene. Urine was collected for the determination of N-terminal cross-linking telopeptide of type I collagen. Muscle strength was measured and Cooper's test was performed. Current exercise, smoking, calcium intake, and alcohol consumption were recorded using a questionnaire. During military service, 15 men experienced a stress fracture, diagnosed with X-ray in 14 and with nuclear magnetic resonance in one man. Those who experienced a fracture were taller than those who did not (P = 0.047). The result of Cooper's test was worse in the fracture group than in the non-fracture group (P = 0.026). Femoral neck and total hip BMC and BMD, adjusted for age, weight, height, exercise, smoking, and alcohol and calcium intake were lower (P = 0.021-0.041) for the fracture group. Stress fractures associated with higher iPTH levels (P = 0.022) but not with lower 25-OHD levels. Bone turnover markers as well as sex hormone and SHBG levels were similar for men with and without stress fracture. There was no difference in the genetic analyses between the groups. In conclusion, tall height, poor physical conditioning, low hip BMC and BMD, as well as high serum PTH level are risk factors for stress fractures in male Finnish military recruits. Given the poor vitamin D status of young Finnish men, intervention studies of vitamin D supplementation to lower serum PTH levels and to possibly reduce the incidence of stress fractures are warranted.