Do dietary calcium and age explain the controversy surrounding the relationship between bone mineral density and vitamin D receptor gene polymorphisms?

Acquisition of peak bone mass

Peak bone mass (PBM) is a key determinant of bone mass and fragility fractures later in life. The increase in bone mass during childhood and adolescence is mainly related to an increase in bone size rather to changes in volumetric bone density. Race, gender, and genetic factors are the main determinants of PBM achievement. Nevertheless, environmental factors such as physical activity, calcium and protein intakes, weight and age at menarche, are also playing an important role in bone mass accrual during growth. Therefore, optimization of calcium and protein intakes and weight-bearing physical activity during growth is an important strategy for optimal acquisition of PBM and bone strength and for contributing to prevent fractures later in life.

Osteoporosis in Premenopausal Women: A Clinical Narrative Review by the ECTS and the IOF

CONTEXT

Consensus regarding diagnosis and management of osteoporosis in premenopausal women (PW) is still lacking due to few studies carried out in this population.

DESIGN

The European Calcified Tissue Society and the International Osteoporosis Foundation convened a working group to produce an updated review of literature published after 2017 on this topic.

RESULTS

Fragility fractures in PW are rare and mostly due to secondary osteoporosis (ie, in presence of an underlying disease such as hormonal, inflammatory, or digestive disorders). In absence of another disorder, low bone mineral density (BMD) together with fragility fractures qualifies as idiopathic osteoporosis. In contrast, low BMD alone does not necessarily represent osteoporosis in absence of bone microarchitectural abnormalities. BMD increases in PW with osteoporosis when the underlying disease is treated. For example, in celiac disease, an increase of 9% in radius trabecular volumetric density was achieved after 1 year of gluten-free diet, while anti-tumor necrosis factor alpha improved BMD in PW with inflammatory bowel diseases. In amenorrhea, including anorexia nervosa, appropriately delivered estrogen replacement therapy can also improve BMD. Alternatively, antiresorptive or anabolic therapy has been shown to improve BMD in a variety of conditions, the range of improvement (3%-16%) depending on skeletal site and the nature of the secondary cause. No studies were powered to demonstrate fracture reduction. The effects of bisphosphonates in childbearing women have been scantly studied and caution is needed.

CONCLUSION

The majority of PW with osteoporosis have an underlying disease. Specific therapy of these diseases, as well as antiresorptive and anabolic drugs, improve BMD, but without evidence of fracture reduction.

Causes of low peak bone mass in women

Peak bone mass is the maximum bone mass that accrues during growth and development. Consolidation of peak bone mass normally occurs during early adulthood. Low peak bone mass results from failure to achieve peak bone mass genetic potential, primarily due to bone loss caused by a variety of conditions or processes occurring at younger ages than usual. Recognized causes of low peak bone mass include genetic causes, endocrine disorders, nutritional disorders, chronic diseases of childhood or adolescence, medications, and idiopathic factors.

Association between vitamin D receptor BsmI polymorphism and bone mineral density in pediatric patients: A meta-analysis and systematic review of observational studies

BACKGROUND

Vitamin D and the vitamin D receptor (VDR) are important in the metabolic processes that affect bone mineral density (BMD). However, the effect of VDR BsmI polymorphism on BMD in pediatric patients is still unclear.

METHODS

Eligible studies were identified from the following electronic databases: PubMed, Embase, the Cochrane Library, and the Chinese CNKI and Wanfang databases before October 1, 2016. Data were extracted from the eligible studies, and associations between VDR BsmI polymorphism and BMD in pediatric patients were estimated with weighted mean differences (WMDs) and 95% confidence intervals (CIs). Subgroup analysis of ethnicity and sensitivity analyses were used to identify sources of heterogeneity.

RESULTS

A significant difference was observed between VDR BsmI polymorphism and pediatric BMD levels of the lumbar spine (LS) in the corecessive model (bb vs BB + Bb: WMD = -0.23, 95% CI [-0.35, -0.11], P < 0.01). No significant relationship was found in the dominant, recessive, or codominant models for LS BMD (BB vs Bb: WMD = -0.56, 95% CI [-1.58, 0.46], P = 0.29; BB vs bb: WMD = -0.54, 95% CI [-1.49, 0.41], P = 0.27; and BB vs Bb + bb: WMD = -0.45, 95% CI [-1.71, 0.26], P = 0.22). In addition, we found no remarkable association between the BsmI polymorphism and BMD levels of the femoral neck (FN) in children (BB vs Bb: WMD = -1.08, 95% CI [-3.13, 0.96], P = 0.30; BB vs bb: WMD = 0.98, 95% CI [-0.89, 2.85], P = 0.31; BB vs Bb + bb: WMD = -0.061, 95% CI [-0.30, 0.17], P = 0.61; and bb vs BB + Bb: WMD = 0.82, 95% CI [-0.59, 2.32], P = 0.25).

CONCLUSION

Our meta-analysis found that the VDR BsmI genetic polymorphism was correlated with LS BMD level in pediatric patients: compared with those with the B allele, children with the bb genotype were less likely to have lower BMD levels. No significant difference was identified in the pediatric FN BMD levels.

Nutritional rickets: vitamin D, calcium, and the genetic make-up

BACKGROUND

The prevalence of vitamin D (vitD) deficiency presenting as rickets is increasing worldwide. Insufficient sun exposure, vitD administration, and/or calcium intake are the main causes. However, vitD system-related genes may also have a role.

METHODS

Prospective study: 109 rachitic children completed a 6-mo study period or until rachitic manifestations disappeared. Thirty children were selected as controls. Clinical and biochemical data were evaluated at baseline in patients and controls and biochemistry re-evaluated at radiological healing. Therapy was stratified in three different protocols. Fifty-four single-nucleotide polymorphisms (SNPs) of five vitD system genes (VDR, CP2R1, CYP27B1, CYP24A1, and GC) were genotyped and their association with clinical and biochemcial data was analyzed.

RESULTS

Therapy response was similar in terms of radiological healing although it was not so in terms of biochemical normalization. Only VDR gene (promoter, start-codon, and intronic genotypes) was rickets-associated in terms of serum 25-OH-D, calcium, radiological severity and time needed to heal. Eight patients with sufficient calcium intake and 25-OH-D levels carried a VDR genotype lacking minor allele homozygous genotypes at SNPs spread along the gene.

CONCLUSION

Although patients presented epidemiologic factors strongly contributing to rickets, genetic modulation affecting predisposition, severity, and clinical course is exerted, at least in part, by VDR gene polymorphic variation.

Genetics of pediatric bone strength

Osteoporosis is one of the most common chronic forms of disability in postmenopausal women and represents a major health burden around the world. Bone fragility is affected by bone mineral density (BMD), and, one of the most important factors in preventing osteoporosis is optimizing peak bone mass, which is achieved during growth in childhood and adolescence. BMD is a complex trait resulting from environmental and genetic factors. Genome-wide association studies have discovered robust genetic signals influencing BMD in adults, and similar studies have also been conducted to investigate the genetics of BMD in the pediatric setting. These latter studies have revealed that many adult osteoporosis-related loci also regulate BMD during growth. These investigations have the potential to profoundly impact public health and will allow for the eventual development of effective interventions for the prevention of osteoporosis.

Vitamin D receptor variability and physical activity are jointly associated with low handgrip strength and osteoporosis in community-dwelling elderly people in Taiwan: the Taichung Community Health Study for Elders (TCHS-E)

We studied 472 elders to assess joint association of vitamin D receptor (VDR) variability and physical activity on low handgrip strength (LHS) and osteoporosis (OST). Our findings showed that higher risks of OST were associated with physically inactive elders with some specific VDR variations, highlighting the importance of promotion program for physical activity.

INTRODUCTION

The aim of this study was to determine the joint association between VDR variability and physical activity on LHS and OST in community-dwelling elders.

METHODS

Bone mineral density of the lumbar spine (LS), the femoral neck (FN), and the total hip were measured by dual-energy X-ray absorptiometry. Four single-nucleotide polymorphisms (SNPs) (rs7975232, rs1544410, rs2239185, and rs3782905) of the VDR gene were examined in 472 participants.

RESULTS

Physical inactivity and each of the four SNPs were jointly associated with a significantly greater risk of LHS in people than that associated with each of the VDR SNPs or low physical activity alone. Physically inactive men with the AG or AA genotype of rs2239185 had a significantly greater risk of overall, LS, and FN OST than those of physically active men with the GG genotype [odds ratio (OR) 3.57, 95 % confidence interval (CI) 1.10-11.65; OR 4.74, 95 % CI 1.43-15.70; and OR 5.06, 95 % CI 1.08-23.71, respectively]. Similarly, physically inactive women with the CG or CC genotype of rs3782905 and the AG or AA genotype of rs1544410 had a significantly greater risk of FN OST than physically active women with the GG genotype (OR 5.33, 95 % CI 1.23-23.06 and OR 5.36, 95 % CI 1.11-25.94, respectively).

CONCLUSIONS

VDR polymorphisms and physical activity are jointly associated with LHS and OST in elders. Health care programs should promote physical activity among elders as a cost-effective way to prevent LHS and OST, especially in those who may be genetically predisposed.

The association between fracture rates and neighborhood characteristics in Washington, DC, children

BACKGROUND

Effects of neighborhood contextual features have been found for many diseases, including bone fractures in adults. Our study objective was to evaluate the association between neighborhood characteristics and pediatric bone fracture rates. We hypothesized that neighborhood indices of deprivation would be associated with higher fracture rates.

MATERIALS AND METHODS

Pediatric bone fracture cases treated at a tertiary, academic, urban pediatric emergency department between 2003 and 2006 were mapped to census block groups using geographical information systems software. Fracture rates were calculated as fractures per 1000 children in each census block. Exploratory factor analysis of socioeconomic indicators was performed using 2000 census block data. Factor scores were used to predict odds of bone fracture at the individual level while adjusting for mean age, sex composition, and race/ethnicity composition at census block level using our sample data.

RESULTS

We analyzed 3764 fracture visits in 3557 patients representing 349 distinct census blocks groups. Fracture rates among census blocks ranged from 0 to 207 per 1000 children/study period. Logistic regression modeling identified 2 factors (race/education and large families) associated with increased fracture risk. Census variables reflecting African American race, laborer/service industry employment, long-term block group residence, and lower education levels strongly loaded on the race/education factor. The large families factor indicated the children-to-families ratio within the block group. The poverty factor was not independently associated with fracture risk.

CONCLUSIONS

Thus, neighborhood characteristics are associated with risk for fractures in children. These results can help inform translational efforts to develop targeted strategies for bone fracture prevention in children.

The effect of FokI vitamin D receptor polymorphism on bone mineral density in Jordanian perimenopausal women

CONTEXT:

Osteoporosis is a polygenic, multifactorial disease that is characterized by demineralization of bone, and thus presented with decreasing bone mineral mass. Vitamin D receptor (VDR) gene polymorphisms in the 3’-end region (as determined by the enzymes BsmI and ApaI) have been inconsistently associated with bone mineral mass. Another important VDR start codon polymorphism (as determined by the enzyme FokI) has been found to be related to adult bone mineral density (BMD) in pre-and post-menopausal American women.

AIMS:

This study aims to investigate the prevalence of the FokI VDR gene polymorphism in Jordanian perimenopausal women and study its relationship with bone mineral density.

MATERIALS AND METHODS:

DNA was isolated from 90 controls (Mean age = 50.41 ± 1.29 y), and 120 patients with symptomatic vertebral fractures (Mean age = 49.14 ± 3.19 y). Restriction Fragment Length Polymorphism (RFLP) analysis of FokI was performed on DNA samples.

STATISTICAL ANALYSIS:

Data was analyzed using SPSS v19 and Microsoft Excel 2007.

RESULTS:

The results showed that in controls, the FF (−0.70 ± 0.51) genotype is associated with high lumbar spine BMD Z-score as compared to Ff (−1.25 ± 0.26) and ff (−1.66 ± 0.47) genotypes (P = 0.0095). In patients, the ff genotype was associated with lower lumbar spine BMD in T-score (−2.31 ± 0.17) and Z-score (−1.56 ± 0.09) genotypes (P = 0.031). No significant association was seen in the femoral neck BMD.

CONCLUSION:

FokI polymorphism may be associated with low BMD in our studied population; however, further studies including other polymorphisms and large sample number are needed.

Vitamin D receptor gene polymorphisms and bone mass indices in post-menarchal Indian adolescent girls

To study the association between vitamin D receptor (VDR) gene polymorphisms and bone mass indices in adolescent girls, a cross-sectional study was conducted in 120 post-menarchal girls aged 15-18 years in Pune city, India. Serum levels of ionised calcium, inorganic phosphorous, parathyroid hormone and 25-hydroxy vitamin-D were measured. Bone mineral content (BMC), bone area (BA) and bone mineral density (BMD) were measured at total body (TB), lumbar spine (LS) and left femoral neck (FN) using dual energy X-ray absorptiometry. Polymorphisms of the VDR gene at the Fok1 and Bsm1 loci were detected using SYBR Green quantitative polymerase chain reaction. The overall distribution of genotypes at the Bsm1 locus in this study was 33.3 % Bb, 29.2 % bb and 37.5 % BB while that for the Fok1 locus was 44.2 % Ff, 7.5 % ff and 48.3 % FF. There were no significant differences in the blood parameters when classified according to Bsm1 or Fok1 genotypes. Subjects with BB genotype have significantly higher mean TBBMC, TBBA, TBBMD and LSBMD than Bb and bb (p < 0.05) and showed a tendency for association with LSBMC and LSBA (p < 0.1). Subjects with Ff genotype showed a tendency for association with left FNBMC and FNBA (p < 0.1). Bsm1 genotype did not show an association with FN bone indices whereas Fok1 genotype did not show association with TB or LS bone indices. In conclusion, the present study demonstrates VDR gene polymorphism, defined by Bsm1 genotype, has an influence on total body and lumbar spine bone mass indices in post-menarchal Indian girls.

Pharmacogenomics of osteoporosis: a pathway approach

Osteoporosis is frequent in postmenopausal women and old men. As with other prevalent disorders, it is the consequence of complex interactions between genetic and acquired factors. Candidate gene and genome-wide association studies have pointed to several genes as determinants of the risk of osteoporosis. Some of them were previously unsuspected and may help to find new therapeutic targets. Several drugs already available are very effective in increasing bone mass and decreasing fracture risk. However, not all patients respond properly and some of them suffer fragility fractures despite therapy. Investigators have tried to identify the genetic features influencing the response to antiosteoporotic therapy. In this article we will review recent data providing insight into new genes involved in osteoporosis and the pharmacogenetic data currently available.

Forearm fractures in children and bone health

PURPOSE OF REVIEW

Summary highlighting the evidence that bone health may affect forearm fracture risk in children.

RECENT FINDINGS

Although the incidence of other fractures and injuries are decreasing, the incidence of forearm fractures is increasing in otherwise healthy children. There is a growing volume of research that forearm fracture risk in children may be related to deficiencies in parameters of bone health. Available evidence of this relationship was summarized and included direct links to bone health (measurement of bone properties), indirect links to bone health (diet, vitamin D status, BMI), and genetic analyses.

SUMMARY

There is consistent and convincing evidence of an association between bone mineral density and forearm fracture risk in children. Studies of calcium intake and supplementation are less extensive in scope but suggest that effects of calcium deficiency on the radius may contribute to childhood forearm fracture risk. Forearm fracture risk in obese children is likely to reflect a combination of suboptimal bone health status and behavioral characteristics. Published data on the role of vitamin D status and genetic factors are limited but merit further consideration. Further investigation is needed to better understand the factors contributing to forearm fracture risk in children and translate this knowledge into effective clinical prevention and practice.

Predictors of bone disease in Egyptian prepubertal children with β-thalassaemia major

INTRODUCTION

Thalassaemic osteopathy is a multifactorial disorder and limited information exists about bone accrual and bone mineral density (BMD) in prepubertal thalassaemic children. The study aimed to investigate some potential genetic and biochemical bone markers as possible early predictors of BMD variations in children with β-thalassaemia major (TM) before puberty.

MATERIAL AND METHODS

Thirt-one prepubertal children with β-TM, and 43 matched controls were subjected to BMD assessment by dual energy X-ray absorptiometry (DEXA). Vitamin D receptor (VDR) gene polymorphisms (Bsm1, Fok1) and the biochemical bone markers serum osteocalcin and propeptide I procollagen (CPIP) and urinary deoxypyridinoline (DPD) excretion were assessed.

RESULTS

Bone mineral density was reduced in 25% of thalassaemics at the spine and 15.4% at the hip region. Significantly higher levels of urinary DPD and lower serum osteocalcin and CPIP levels were found in the studied thalassaemic children compared to controls (p < 0.001). A significant negative correlation was present between BMD in spine and hip and the patients' age (r = -0.6367, p = 0.0002 and r = -0.616, p = 0.00079, respectively). There was a significant reduction in BMD in males compared to females. Reduced BMD was more frequent in male patients with genotypes bb and Ff but not in females. Bone mineral density was not related to the studied biochemical bone markers, mean pre-transfusion haemoglobin or serum ferritin.

CONCLUSIONS

Routine BMD screening with DEXA is proposed to be a sensitive predictor for early bone changes, particularly at the lumbar spine. DR gene polymorphisms of Bsm1 and Fok1 polymorphisms may be determinants of BMD in Egyptian prepubertal male thalassemics.

Effect of age, gender and calciotropic hormones on the relationship between vitamin D receptor gene polymorphisms and bone mineral density

BACKGROUND/OBJECTIVES

Hypovitaminosis D is a major public health problem worldwide and unexpectedly more so in sunny countries. Vitamin D receptor (VDR) gene is associated with inter-individual variance in bone mineral density (BMD). Studies assessing the effect of VDR gene polymorphisms on BMD yielded conflicting results. The aim of this study was to assess the relationship between VDR polymorphisms and BMD in the Lebanese, across age groups and genders and to assess the effect of PTH and lean mass and vitamin D levels on such relationship.

SUBJECTS/METHODS

In total, 203 subjects aged 65-85 years and 336 children aged 10-17 years. Polymorphisms in the VDR gene were assessed with the restriction enzymes BsmI, TaqI and ApaI. Bone mineral content, BMD and lean mass were measured using Dual-Energy X-ray Absorptiometry (DXA). The dominant hand strength was measured in children.

RESULTS

Heterozygote genotype was the most frequent in both age groups. There was no difference in the frequency distribution of genotypes between the young and the elderly. No relationship between VDR genotypes and lean mass was found in either age group. Heterozygote boys had the lowest parathormone (PTH) and heterozygote elderly women had the highest BMD at the spine and forearm.

CONCLUSIONS

In the Lebanese, the relationship between VDR polymorphisms and BMD differs by age. Survival does not seem to differ by VDR genotype. However, further studies are needed to assess the effect of VDR gene polymorphisms on mortality per se and time to mortality, not evaluated in this study.

Pharmacogenetic risk factors for altered bone mineral density and body composition in pediatric acute lymphoblastic leukemia

BACKGROUND

This study investigates pharmacogenetic risk factors for bone mineral (apparent) density (BM(A)D) and body composition in pediatric acute lymphoblastic leukemia

DESIGN AND METHODS

We determined the influence of SNPs in 4 genes (vitamin-D receptor (VDR: BsmI/ApaI/TaqI and Cdx-2/GATA), collagen type I alpha 1 (SpI), estrogen receptor 1 (ESR1: PvuII/XbaI), glucocorticoid receptor (BclI)) on body composition, BM(A)D and fracture risk during dexamethasone-based pediatric acute lymphoblastic leukemia treatment. Body composition and BMD were measured repeatedly during and after treatment using dual energy X-ray absorptiometry.

RESULTS

Non-carriers of VDR 5'-end (Cdx-2/GATA) haplotype 3 revealed a significant larger fat gain than carriers (Delta%fat: non-carriers: +1.76SDS, carriers: +0.77SDS, P<0.001). At diagnosis and during therapy, lumbar spine BMD was significantly higher in non-carriers of VDR 5'-end (Cdx-2/GATA) haplotype 3 than in carriers. The other SNPs did not influence BMD or fracture risk during/after treatment. The year after treatment completion, lean body mass increased in non-carriers of ESR1 (PvuII/XbaI) haplotype 3 and decreased in carriers (Delta lean body mass: non-carriers:+0.28SDS, carriers: -0.55SDS, P<0.01).

CONCLUSIONS

Only VDR 5'-end (Cdx-2/GATA) haplotype 3 was identified as protective factor against excessive fat gain and as a risk factor for lower lumbar spine BMD during treatment. Carrying ESR1 (PvuII/XbaI) haplotype 3 negatively influenced recovery of lean body mass after pediatric acute lymphoblastic leukemia treatment.

Update on the pharmacogenetics of the vitamin D receptor and osteoporosis

Vitamin D and calcium are essential for normal skeletal growth and for maintaining the mechanical and structural integrity of the skeleton. Reduced intake of calcium and vitamin D may be associated with reduced bone mass and osteoporosis while a chronic and severe vitamin D deficiency may lead to osteomalacia. Given the importance of vitamin D in bone homeostasis, common polymorphisms in the vitamin D receptor gene were the first to be investigated as possible determinants of bone mass and fracture risk. Even though results are still conflicting and the molecular mechanisms by which these polymorphisms influence receptor activity remain in part to be investigated, an additional important issue is represented by their potential pharmacogenomic and pharmacogenetic implications. This review analyzes major pharmacogenetic studies of polymorphisms in the vitamin D receptor gene and osteoporosis.

Rickets in the Middle East: role of environment and genetic predisposition

CONTEXT

The Middle East has a high incidence of rickets, and it is also common in Europe-dwelling children of Middle Eastern origin.

OBJECTIVE

The objective of the study was to explore the mechanisms leading to rickets in children of the Middle East.

DESIGN AND SETTING

We conducted a prospective study in 98 rachitic and 50 controls (aged 6 months to 4 yr) from university and community outpatient hospitals in Egypt and Turkey.

MAIN OUTCOME MEASURES

We collected epidemiological, maternal, nutritional, radiographic, and biochemical parameters; markers of bone turnover; and vitamin D receptor (VDR) gene polymorphisms.

RESULTS

Epidemiological factors had a key role in pursuit of rickets; Egyptian and Turkish patients had lower (P < 0.01) dietary calcium intake than controls and the recommended dietary intakes, and serum 25-hydroxyvitamin D levels were reduced in patients, the difference with controls being significant (P < 0.001) only in Turkey, although rickets was more severe in Egypt as determined by the x-ray score (P < 0.05). In Turkey, the F VDR allele frequency was significantly (P < 0.05) increased in patients. The BB VDR genotype was associated with lower serum 25-hydroxyvitamin D levels in both patients and controls and with severity of rickets.

CONCLUSIONS

In Turkey most patients had vitamin D deficiency, whereas in Egypt they had mostly calcium insufficiency combined with vitamin D deficiency. In this environ, VDR genotypes may predispose to rickets by increased frequency of the F allele. The unique environs and genetic predisposition have to be accounted for in the design of preventive measures, rather than using European or American recommended dietary intake for calcium and vitamin D.

Bone mass and breast milk calcium concentration are associated with vitamin D receptor gene polymorphisms in adolescent mothers

Lactation-associated bone loss has been reported in adolescent mothers. Polymorphisms in the vitamin D receptor (VDR) gene may contribute to differences in the physiologic skeletal response to lactation in these mothers. We evaluated the influence of VDR gene polymorphisms ApaI, BsmI, and TaqI on bone mass, bone and calcium-related hormones, and breast milk calcium of lactating adolescents with habitually low calcium intake. Total body bone mineral content (TBMC), total body bone mineral density (TBMD), lumbar spine BMD (LSBMD), serum hormones [intact parathyroid hormone (iPTH), 25-hydroxyvitamin D, insulin-like growth factor-I (IGF1), prolactin, and estradiol), and breast milk calcium were measured in 40 lactating Brazilian adolescents (15-18 y), and compared by VDR genotype subgroups after adjustment for calcium intake and postmenarcheal and lactational periods. TBMD and LSBMD Z scores were -0.55 +/- 1.01 and -1.15 +/- 1.48, respectively. LSBMD was higher (21%; P < 0.05) in adolescents with the aa genotype (n = 5) compared with those with the AA genotype (n = 7). TBMC and IGF1 were higher (23 and 50%, respectively; P < 0.05) in adolescents with tt (n = 4) than those with TT (n = 29) and Tt (n = 7) genotypes. Breast milk calcium and serum iPTH were higher (24 and 80%, respectively; P < 0.05) in adolescents with bb (n = 8) compared with those with BB (n = 21) genotype. These results indicate that bone mass and breast milk calcium are significantly associated with VDR genotypes in lactating Brazilian adolescents. Those with aa and tt genotypes had a better bone status and those with bb genotype had greater breast milk calcium.

Recent development in pharmacogenomics: from candidate genes to genome-wide association studies

Genetic diversity, most notably through single nucleotide polymorphisms and copy-number variation, together with specific environmental exposures, contributes to both disease susceptibility and drug response variability. It has proved difficult to isolate disease genes that confer susceptibility to complex disorders, and as a consequence, even fewer genetic variants that influence clinical drug responsiveness have been uncovered. As such, the candidate gene approach has largely failed to deliver and, although the family-based linkage approach has certain theoretical advantages in dealing with common/complex disorders, progress has been slower than was hoped. More recently, genome-wide association studies have gained increasing popularity, as they enable scientists to robustly associate specific variants with the predisposition for complex disease, such as age-related macular degeneration, Type 2 diabetes, inflammatory bowel disease, obesity, autism and leukemia. This relatively new methodology has stirred new hope for the mapping of genes that regulate drug response related to these conditions. Collectively, these studies support the notion that modern high-throughput single nucleotide polymorphism genotyping technologies, when applied to large and comprehensively phenotyped patient cohorts, will readily reveal the most clinically relevant disease-modifying and drug response genes. This review addresses both recent advances in the genotyping field and highlights from genome-wide association studies, which have conclusively uncovered variants that underlie disease susceptibility and/or variability in drug response in common disorders.

Association of vitamin D receptor polymorphism with calcaneal broadband ultrasound attenuation in Korean postmenopausal women with low calcium intake

This study investigated the associations among vitamin D receptor (VDR)BsmI polymorphism, calcium intake and bone strength as indicated by the broadband ultrasound attenuation (BUA) measured by calcaneal quantitative ultrasound at the left calcaneus in community-dwelling subjects with a low calcium intake. The VDRBsmI polymorphism was analysed in 335 women older than 65 years residing in rural Asan, Korea. Calcium intake was assessed with a 2 d, 24 h recall method. The distribution of genotypes was similar to that reported in other Asian populations (92 % bb, 7 % Bb and 1 % BB). The calcaneal BUA was significantly higher (P = 0·013) in the bb genotype than in the Bb or BB genotype (Bb and BB genotypes were combined due to the small number of BB subjects) in a multiple regression model after adjusting for age, body weight, height, physical activity and nutritional factors. BUA was not significantly affected by the calcium intake regardless of the genotype, cross-sectionally. The energy-adjusted average calcium intake of this population was 439·6 mg/d (432·5 mg/d for bb and 522·3 mg/d for Bb or BB), and 96 % of the subjects had dietary intakes that were less than the recommended Dietary Reference Intake for Koreans (which for calcium is 800 mg/d for women older than 65 years). In summary, the BUA in older Korean women with a low calcium intake was significantly influenced by the VDR genotype but not by the calcium intake, cross-sectionally.

Steroid hormone receptor gene polymorphisms and osteoporosis: a pharmacogenomic review

Osteoporosis is a common skeletal disorder with a strong genetic component. In recent years, significant progress has been made in understanding the genetic basis of osteoporosis. Given the biological significance of signalling through steroid hormone receptors, bone biology and calcium homeostasis, alleles of steroid hormone receptor genes have been postulated to contribute to the well-documented genetic predisposition to osteoporosis; and in different studies, these alleles have been associated with variation in bone mass and fracture risk. Even though results are still conflicting and the molecular mechanisms by which these polymorphisms influence receptor activity remain, in part, to be investigated, an additional important issue is represented by potential pharmacogenomic (the investigation of variations of DNA or RNA characteristics as related to drug response) or pharmacogenetic (the influence of variations of DNA sequence on drug response) implications. In fact, steroid hormone receptors actually mediate the action of several compounds known to positively or negatively affect bone homeostasis, such as vitamin D, estrogen and glucocorticoids. This review analyses major pharmacogenetic studies of polymorphisms in steroid hormone receptor genes.

A genetic approach to fracture epidemiology in childhood

The purpose of this report is to provide a review of both childhood fracture epidemiology and known heritable causes for fracture predisposition to the Medical Geneticist, who is frequently consulted to assess children with multiple or unexplained fractures for a physiologic etiology. A detailed knowledge of the clinical and laboratory evaluation for osteogenesis imperfecta (OI) and other single-gene disorders is obviously essential to complete a useful evaluation of such children. The experienced clinician will immediately recognize that single gene disorders represent only a small fraction of these patients. In infants, non-accidental trauma (NAT) unfortunately is the likely explanation for the fracture pattern, but in some infants, and certainly in older children with recurrent fractures, no medical explanations can be found. Recent studies in which bone mineral density (BMD) has been associated with genetic variation at a number of candidate genes are promising but these studies are too premature yet to be used clinically. Nonetheless, we do expect that in the future whole-genome approaches in conjunction with key clinical and epidemiological variables may be combined through an informatics approach to create better predictors of fracture susceptibility for these populations of patients.

FokI and BsmI polymorphisms of the vitamin D receptor gene and bone mineral density in a random Bulgarian population sample

Numerous studies on vitamin D receptor (VDR) gene polymorphisms differ with conflicting data in various populations. We studied the association of FokI and BsmI polymorphisms in the gene encoding the vitamin D receptor with bone mineral density (BMD) in 219 persons of Bulgarian nationality. The calculated relative risk (RR) for low bone mineral density is higher for FokI marker (3.14) compared to BsmI marker (2.44). The etiological factor (EF), which shows association between polymorphisms investigated and illness on populational level, is defined as EF = 0.51 for FokI marker and EF = 0.42 for BsmI marker. Because of this we conclude that FokI and BsmI polymorphisms are closely related to low BMD at the forearm and lumbar spine. Both polymorphisms are useful genetic markers in determining BMD and osteoporosis risk. Further studies of larger cohorts and in ethnically diverse subgroups are necessary.

Vitamin D and estrogen receptor-alpha genotype and indices of bone mass and bone turnover in Danish girls

Peak bone mass is a major determinant of osteoporosis risk in later life. It is under strong genetic control; however, little is known about the identity of the genes involved. In the present study, we investigated the relationship between polymorphisms in the genes encoding the vitamin D receptor (VDR) (FokI, TaqI) and estrogen receptor-alpha (ERalpha) (PvuII, XbaI), and bone mineral density (BMD), bone mineral content (BMC), and markers of bone turnover in 224 Danish girls aged 11-12 years. BMD and BMC were measured by dual-energy X-ray absorptiometry. Serum osteocalcin, 25(OH)D, and parathyroid hormone (PTH) were measured by ELISA assays and urinary pyridinium cross-links by HPLC. Physical activity, dietary calcium, and Tanner stage were assessed by questionnaire. In general, there were no significant differences in anthropometrical variables, physical activity, dietary calcium, serum 25(OH)D, or PTH among genotype groups. BMD or BMC of lumbar spine or whole body (adjusted for body and bone size and pubertal status) were not associated with VDR or ERalpha genotypes or the combination of these genotypes. This lack of association remained even after adjustment for dietary and environmental factors. VDR genotypes had no effect on bone turnover markers. XX and PP ERalpha genotypes were associated (P < 0.05) with reduced levels of urinary pyridinium cross-links, whereas serum osteocalcin was similar among genotypes. These findings suggest that the rate of bone resorption was influenced by ERalpha genotypes, even though these biochemical differences were not evident in bone mass indices.

Pathogenesis of osteoporosis: concepts, conflicts, and prospects

Osteoporosis is a disorder in which loss of bone strength leads to fragility fractures. This review examines the fundamental pathogenetic mechanisms underlying this disorder, which include: (a) failure to achieve a skeleton of optimal strength during growth and development; (b) excessive bone resorption resulting in loss of bone mass and disruption of architecture; and (c) failure to replace lost bone due to defects in bone formation. Estrogen deficiency is known to play a critical role in the development of osteoporosis, while calcium and vitamin D deficiencies and secondary hyperparathyroidism also contribute. There are multiple mechanisms underlying the regulation of bone remodeling, and these involve not only the osteoblastic and osteoclastic cell lineages but also other marrow cells, in addition to the interaction of systemic hormones, local cytokines, growth factors, and transcription factors. Polymorphisms of a large number of genes have been associated with differences in bone mass and fragility. It is now possible to diagnose osteoporosis, assess fracture risk, and reduce that risk with antiresorptive or other available therapies. However, new and more effective approaches are likely to emerge from a better understanding of the regulators of bone cell function.

Gene variants for osteoporosis and their pleiotropic effects in aging

The prevalence of osteoporosis is raising worldwide as improving conditions of living and treatment of other common diseases continuously increases life expectancy. Thus, osteoporosis affects most women above 80 years of age and, at the age of 50, the lifetime risk of suffering an osteoporosis-related fracture approaches 50% in women and 20% in men. Numerous genetic, hormonal, nutritional and life-style factors contribute to the acquisition and maintenance of bone mass. Among them, genetic variations explain as much as 70% of the variance for bone mineral density (BMD) in the population. Dozens of quantitative trait loci (QTLs) for BMD have been identified by genome screening and linkage approaches in humans and mice, and more than 100 candidate gene polymorphisms tested for association with BMD and/or fracture. Sequence variants in the vitamin D receptor (VDR), collagen 1 alpha 1 chain (Col1A1), estrogen receptor alpha (ESR1), interleukin-6 (IL-6) and LDL receptor-related protein 5 (LRP5) genes were all found to be significantly associated with differences in BMD and/or fracture risk in multiple replication studies. Moreover, some genes, such as VDR and IL-6, were shown to interact with non-genetic factors, i.e. calcium intake and estrogens, to modulate BMD. Since these gene variants have also been associated with other complex disorders, including cancer and coronary heart disease, they may represent common genetic susceptibility factors exerting pleiotropic effects during the aging process.

Vitamin D receptor Fok1 polymorphisms affect calcium absorption, kinetics, and bone mineralization rates during puberty

Few studies of the VDR polymorphisms have looked at calcium metabolism or long-term effects. We measured bone mineralization and calcium metabolic parameters longitudinally in a group of 99 adolescents. We found a significant relationship between calcium absorption and skeletal calcium accretion and the Fok1, but not other VDR or related, genetic polymorphisms. It seems that the Fok1 polymorphism directly affects bone mineralization during pubertal growth through an effect on calcium absorption.

INTRODUCTION

There are few data regarding the relationship between genetic markers for low bone mass and changes in calcium metabolism in childhood or adolescence. We sought to identify the effects of polymorphisms of the vitamin D receptor (VDR) on calcium and bone mineral metabolism in a longitudinal study of pubertal adolescents.

MATERIALS AND METHODS

Adolescents (n = 99) received comprehensive stable isotope studies of calcium absorption, bone calcium kinetics, and bone mineralization. Studies were repeated 12 months later. Polymorphisms of putative genetic markers were determined and related to bone mineralization and calcium metabolic finding. Results were analyzed by ANOVA in which changes over time were determined using the initial value as a covariate.

RESULTS

Polymorphisms of the Fok1 gene of the VDR were significantly related to calcium absorption (p = 0.008) and whole body BMC (p = 0.03) and BMD (p = 0.006). The Fok1 effect on whole body BMD was significant for those with Ca intake >800 mg/day (p < 0.001), whereas for those with Ca intake < or = 800 mg/day, the Fok1 genotype did not have a significant effect on whole body BMD (p = 0.40). The Fok1 genotype was significantly related to the changes during the year in whole body calcium accretion, with the ff genotype having a 63 +/- 20 mg/day deficit compared with the FF genotype (p = 0.008).

CONCLUSIONS

The Fok1 polymorphism of the VDR receptor seems to directly affect bone mineral accretion during pubertal growth through an effect on calcium absorption. The relationship between different genetic polymorphisms and bone mineral metabolism may vary by life stage as well as diet.

Bone mass acquisition in healthy children

Although 80% of the variance in bone mass is determined genetically, there are many other factors which influence the accumulation of bone in early life and affect future risks of osteoporosis. This review considers the genetic, fetal, and environmental influences on bone mass acquisition in healthy children, and highlights important areas where paediatricians may have a role by counselling children and their families to adopt a healthy lifestyle which promotes bone health.

Treatment with intermittent calcitriol and calcium reduces bone loss after renal transplantation

BACKGROUND

Bone loss occurs during the first 6 months after renal transplantation (RT), and corticosteroid therapy plays an important role. Although calcium plus vitamin D administration prevents corticosteroid-induced osteoporosis, its use in RT recipients is limited by the risk of hypercalcemia.

METHODS

This double-blind, randomized, and controlled prospective intervention trial examined the effect of intermittent calcitriol (0.5 microg/48 h) during the first 3 months after RT, plus oral calcium supplementation (0.5 g/day) during 1 year with calcium supplementation alone. The primary outcome measure was the change in bone mineral density (BMD) at 3 and 12 months after RT; we also explored whether the effect of calcitriol on BMD was different among vitamin D receptor (VDR) genotypes (BsmI). Forty-five recipients were randomized to calcitriol therapy (CT) and 41 were randomized to placebo (PL).

RESULTS

Both groups had a similar degree of pre-existing hyperparathyroidism (197 +/- 229 vs. 191 +/- 183 pg/mL), but a more pronounced decrease of parathyroid hormone (PTH) levels after RT was observed in CT patients (at 3 months: 61.4 +/- 42.2 vs. 85.7 +/- 53.1 pg/mL, P= 0.02; at 12 months: 67.3 +/- 33.7 vs. 82.6 +/- 37 pg/mL; P= 0.08). CT patients preserved their BMD at the total hip significantly better than those on PL (3 months: 0.04 +/- 3.3 vs. -1.93 +/- 3.2%, P= 0.01; 12 months: 0.32 +/- 4.8 vs. -2.17 +/- 4.4%, P= 0.03); significant differences were noted at the intertrochanter, trochanter, and Ward's triangle. Differences did not reach significance at the femoral neck. Two CT patients (4.4%) and 4 PL patients (9.8%) developed a hypercalcemic episode during the first 3 months after RT. The effect of CT on BMD at 3 months was more prominent in recipients with the at-risk allele of the VDR gene (P= 0.03).

CONCLUSION

Therapy with low-dose calcium supplements during 1 year, plus intermittent calcitriol for 3 months after RT, is safe, decreases PTH levels more rapidly, and prevents bone loss at the proximal femur; a more pronounced effect is seen in recipients with at least one at-risk allele of the VDR genotype.

The influence of VDR genotype and exercise on ultrasound parameters in young adult Japanese women

We investigated the relation between the vitamin D receptor (VDR) genotype and bone mass including the effect of exercise history as a measure of physical activity. BUA (broadband ultrasound attenuation), SOS (speed of sound) and Stiffness index of the calcaneus were measured using an ultrasound bone densitometer in 105 Japanese young adult women (age: mean+/-SD 20.4+/-4.1 years, ranged 18-37) by the calcaneal ultra sound measurement to assess bone mass. Physical activity was measured using a questionnaire about exercise and was calculated as exercise hours per week during prepuberty (elementary school), puberty (junior and senior high school) and a current period (from >18 years old). VDR genotype was determined by the BsmI restriction site of the VDR gene. Significant differences were observed in age-adjusted and menarche age-adjusted SOS and Stiffness between BsmI VDR genotypes. We also examined the interaction between VDR genotype and the amount of exercise. The association between ultrasound parameters and exercise hours per week was evaluated with simple regression analysis according to VDR genotype. There was a significant difference in the slope between VDR genotypes in regression analysis of exercise hours per week during senior high school for SOS (P<0.05). Furthermore, we conducted multiple regression analysis to examine the contribution of each factor to ultrasound parameters. VDR genotype was a significant independent variable for SOS (P<0.05). Exercise hours each week during senior high school was a significant independent variable for all ultrasound parameters (all: P<0.001). In conclusion, there was a partial significant relation between VDR genotype and ultrasound parameters, but the exercise hours each week during senior high school was the strongest independent factor for bone mass in young adult Japanese women.

Polymorphisms in the low-density lipoprotein receptor-related protein 5 (LRP5) gene are associated with variation in vertebral bone mass, vertebral bone size, and stature in whites

Stature, bone size, and bone mass are interrelated traits with high heritability, but the major genes that govern these phenotypes remain unknown. Independent genomewide quantitative-trait locus studies have suggested a locus for bone-mineral density and stature at chromosome 11q12-13, a region harboring the low-density lipoprotein receptor-related protein 5 (LRP5) gene. Mutations in the LRP5 gene were recently implicated in osteoporosis-pseudoglioma and "high-bone-mass" syndromes. To test whether polymorphisms in the LRP5 gene contribute to bone-mass determination in the general population, we studied a cross-sectional cohort of 889 healthy whites of both sexes. Significant associations were found for a missense substitution in exon 9 (c.2047G-->A) with lumbar spine (LS)-bone-mineral content (BMC) (P=.0032), with bone area (P=.0014), and with stature (P=.0062). The associations were observed mainly in adult men, in whom LRP5 polymorphisms accounted for <or=15% of the traits' variances. Results of haplotype analysis of five single-nucleotide polymorphisms in the LRP5 region suggest that additional genetic variation within the locus might also contribute to bone-mass and size determination. To confirm our results, we investigated whether LRP5 haplotypes were associated with 1-year gain in vertebral bone mass and size in 386 prepubertal children. Significant associations were observed for changes in BMC (P=.0348) and bone area (P=.0286) in males but not females, independently supporting our observations of a mostly male-specific effect, as seen in the adults. Together, these results suggest that LRP5 variants significantly contribute to LS-bone-mass and size determination in men by influencing vertebral bone growth during childhood.

Nutrition influences bone development from infancy through toddler years

During the last decade a greater appreciation has developed for determining factors that influence bone accretion in healthy children. Nutritional factors that may contribute to bone accretion in infants and toddlers include maternal nutritional status during pregnancy, type of infant feeding, calcium and phosphorus content of infant formula, introduction of weaning foods, and diet during the toddler and preschool years. Maternal vitamin D deficiency during pregnancy is associated with disturbances in neonatal calcium homeostasis, and maternal calcium deficiency leads to reduced neonatal bone mineral content (BMC). Preterm infants are at increased risk of osteopenia, and, although the use of high mineral formula has reduced the risk of osteopenia in these infants, it has not eliminated it. The reason for the long-term bone deficiency among preterm infants is not clear, although lower physical activity levels have been suggested as a potential cause. Studies find that human milk-fed infants have lower bone accretion than do formula-fed infants; that the greater the mineral content of formula, the greater the bone accretion; and that the inclusion of palm olein oil in infant formula may reduce bone mineral accretion. Bone accretion is not influenced by the timing of the introduction of weaning foods, despite higher serum parathyroid hormone (PTH) concentrations among infants who receive solids earlier. There is evidence of calcium intake-by-gene and calcium intake-by-physical activity interactions among toddlers and young children. The long-term effects of these early nutritional influences on later bone health are unknown.

Current limitations of SNP data from the public domain for studies of complex disorders: a test for ten candidate genes for obesity and osteoporosis

BACKGROUND

Public SNP databases are frequently used to choose SNPs for candidate genes in the association and linkage studies of complex disorders. However, their utility for such studies of diseases with ethnic-dependent background has never been evaluated.

RESULTS

To estimate the accuracy and completeness of SNP public databases, we analyzed the allele frequencies of 41 SNPs in 10 candidate genes for obesity and/or osteoporosis in a large American-Caucasian sample (1,873 individuals from 405 nuclear families) by PCR-invader assay. We compared our results with those from the databases and other published studies. Of the 41 SNPs, 8 were monomorphic in our sample. Twelve were reported for the first time for Caucasians and the other 29 SNPs in our sample essentially confirmed the respective allele frequencies for Caucasians in the databases and previous studies. The comparison of our data with other ethnic groups showed significant differentiation between the three major world ethnic groups at some SNPs (Caucasians and Africans differed at 3 of the 18 shared SNPs, and Caucasians and Asians differed at 13 of the 22 shared SNPs). This genetic differentiation may have an important implication for studying the well-known ethnic differences in the prevalence of obesity and osteoporosis, and complex disorders in general.

CONCLUSION

A comparative analysis of the SNP data of the candidate genes obtained in the present study, as well as those retrieved from the public domain, suggests that the databases may currently have serious limitations for studying complex disorders with an ethnic-dependent background due to the incomplete and uneven representation of the candidate SNPs in the databases for the major ethnic groups. This conclusion attests to the imperative necessity of large-scale and accurate characterization of these SNPs in different ethnic groups.

Interaction effects between estrogen receptor α gene, vitamin D receptor gene, age, and sex on bone mineral density in Chinese

We evaluated the interaction effects between the estrogen receptor alpha gene (ER-alpha), vitamin D receptor gene (VDR), age and sex on bone mineral density (BMD) in a sample of 340 unrelated males and 297 unrelated females from 401 Chinese nuclear families. Polymorphisms of PvuII and XbaI in the ER-alpha gene and ApaI in the VDR gene were detected by RFLP, and ER-alpha genotype was defined by the haplotype reconstructed according to the two loci. In the females, significant ER-VDR gene interaction ( P<0.05) was found on the lumbar spine BMD. Such interaction might account for approximately 1.0% of the BMD variation. At the femoral neck and trochanter, significant ER-age interaction effects were observed, which might explain 0.3% BMD variation for both skeletal sites. In the males, significant VDR-age interaction was found on femoral neck BMD ( P<0.05), and it accounted for 0.6% BMD variation. These interaction effects were largely dependent on gender groups, suggesting there may exist ER-VDR-sex, ER-age-sex, and VDR-age-sex complex interactions in our Chinese sample.

Interaction of science, consumer practices and policy: calcium and bone health as a case study

Data to support a relationship between calcium and bone health are a major part of the body of evidence that underlie calcium-related policy in the United States. Examples of these policies include dietary intake recommendations, health claims for calcium and osteoporosis on food labels and an objective to improve calcium intake of the U.S. population in Healthy People 2010. Median calcium intakes among females fall below recommended levels after childhood even when supplemental calcium intakes are included. This is a concern in light of data that support a positive relationship between calcium and bone health. Most of the studies on the calcium-bone relationship have focused on older women, and several have used fracture as the endpoint; a meta-analysis of their results suggests that increased calcium intake is associated with approximately 30% decrease in fracture risk. Studies in children, adolescents and premenopausal women have focused on the relationship between calcium and bone mineral density rather than fracture; most of these also support a positive relationship between calcium intake and skeletal health although some data gaps remain. Calcium appears to be a threshold nutrient (e.g., intakes above a certain level do not result in further benefit to bone). The effect of increased calcium intake on bone density does not appear to persist unless the higher intakes are sustained. There are certain conditions, such as lactation, during which calcium intake does not appear to influence bone. Other factors that may influence the effect of calcium on bone include bone-specific genotypes and physical activity.

Establishment of peak bone mass

Among the main areas of progress in osteoporosis research during the last decade or so are the general recognition that this condition, which is the cause of so much pain in the elderly population, has its antecedents in childhood and the identification of the structural basis accounting for much of the differences in bone strength among humans. Nevertheless, current understanding of the bone mineral accrual process is far from complete. The search for genes that regulate bone mass acquisition is ongoing, and current results are not sufficient to identify subjects at risk. However, there is solid evidence that BMD measurements can be helpful for the selection of subjects that presumably would benefit from preventive interventions. The questions regarding the type of preventive interventions, their magnitude, and duration remain unanswered. Carefully designed controlled trials are needed. Nevertheless, previous experience indicates that weight-bearing activity and possibly calcium supplements are beneficial if they are begun during childhood and preferably before the onset of puberty. Modification of unhealthy lifestyles and increments in exercise or calcium assumption are logical interventions that should be implemented to improve bone mass gains in all children and adolescents who are at risk of failing to achieve an optimal peak bone mass.

Vitamin D receptor gene polymorphism and bone metabolism during low-dose oral contraceptive use in young women

With the aim to determine whether bone metabolism in young women using low-dose oral contraception is influenced by vitamin D receptor (VDR) genotype, we designed the prospective clinical study of 41 healthy women aged 20-27 years. Twenty-one women of the study group were prescribed an oral contraceptive (30 microg ethynyl estradiol and 150 microg levonorgestrel) and 20 women of the control group a nonhormonal contraceptive or none. Biochemical markers of bone metabolism (bone-specific alkaline phosphatase, osteocalcin, deoxypyridinoline) and VDR genotype, using BsmI endonuclease, were determined. After 3 months in the study group, the BB genotype subgroup showed significantly decreased osteocalcin (p = 0.010), in the Bb genotype subgroup bone-specific alkaline phosphatase (p = 0.043) and osteocalcin (p = 0.006) decreased, and in the bb genotype subgroup no changes were observed. In the control group, there were no significant changes in markers of bone metabolism regarding VDR genotype. In conclusion, our study shows that in young women VDR gene polymorphism could influence bone metabolism during low-dose oral contraceptive use.

Low peak bone mineral density in healthy Lebanese subjects

Osteoporosis is a major public health problem in Western countries and is projected to have a similar impact in the Middle East. It has been suggested that peak bone mineral density (BMD), a major determinant of osteoporotic fractures later in life, may be lower in this part of the world compared with the Western world. However, subjects have not been randomly selected or systematically screened to rule out secondary causes of bone loss. The purpose of this study was to determine peak bone mass and lifestyle risk factors for bone loss in a randomly chosen sample of healthy Lebanese subjects from the greater Beirut area. Subjects 25-35 years of age were randomly selected from greater Beirut, which comprises one third of the Lebanese at large, and studied during the Fall of 1999. BMD was measured at the lumbar spine, hip, forearm, and total body. A questionnaire on lifestyle factors was administered to all subjects. Results were compared with the database of subjects from the USA provided by the manufacturer, and to the NHANES database for the total hip. Two hundred thirteen subjects were studied; 45 subjects rotated at all three centers for cross-calibration purposes. Peak BMD in Lebanese subjects was 0.2-0.9 SD below that of peak BMD in American subjects, depending on skeletal site, gender, and densitometer. These differences persisted after attempting to adjust for body size. Osteoporosis and osteopenia were more prevalent than in healthy young Americans. Height, weight, and total body fat were the most significant correlates of BMD/bone mineral content (BMC), accounting for 0.3-0.7 of the variance in bone mass measurement. Lifestyle factors had a very modest but significant contribution to bone mass variance. This is the first population-based study from the Middle East demonstrating that peak BMD is slightly lower in Lebanese subjects compared as with an established database from the USA. Due to the selection of relatively healthier subjects in our study than in the NHANES study, the actual differences between the two populations may be even greater. The impact of our findings on the epidemiology of osteoporotic fractures in Lebanon remains to be determined.

Genetics of osteoporosis: role of steroid hormone receptor gene polymorphisms

Osteoporosis is a common skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue with a consequent increase in bone fragility and susceptibility to fracture. In the past years, twin and family study have shown that this disease recognizes a strong genetic component and that genetic factors play an important role in regulating bone mineral density (BMD). While in few isolate conditions osteoporosis can be inherited in a simple Mendelian pattern, due to single gene mutations, in the majority of cases has to be considered a multifactorial polygenic disease in which genetic determinants are modulated by hormonal, environmental and nutritional factors. Given the important role that steroid hormones play in bone cell development and in the maintenance of normal bone architecture, polymorphisms at receptor of the steroid/thyroid hormone receptor superfamily, such as estrogen receptor alpha (ERalpha) and Vitamin D receptor (VDR) have been thoroughly investigated in the last years and appeared to represent important candidate genes. The individual contribution of these genetic polymorphisms to the pathogenesis of osteoporosis remains to be universally confirmed and an important aim in future work will be to define their functional molecular consequences and how these polymorphisms interact with each other and with the environment to cause the osteoporotic phenotype. A further promising application of genetic studies in osteoporosis comes from their pharmacogenomic implications, with the possibility to give a better guidance for therapeutic agents commonly used to treat this invalidating disorder or to identify target molecules for new therapeutic agents.

Genetics of menopause-associated diseases

Menopause is the permanent cessation of menstruation resulting from the loss of ovarian follicular activity. It is estimated that perhaps 50 million women worldwide will go into menopause annually. Atherosclerotic cardiovascular disease, osteoporotic fractures and Alzheimer's dementia are common chronic disorders after menopause, representing major health problems in most developed countries. Apart from being influenced by environmental factors, these chronic disorders recognize a strong genetic component, and there are now considerable clinic evidences that these disorders are related to low hormonal milieu of postmenopausal women. Here, we review up-to-date available data suggesting that genetic variation may contribute to higher susceptibility to four sporadic chronic syndromes such as osteoporosis (OP), osteoarthritis (OA), Alzheimer's disease (AD) and coronary artery disease (CAD). For these four syndromes candidate genes that today appear as major loci in genetic susceptibility encode for proteins specific of a given system, as the vitamin D receptor (VDR) gene for the skeleton and, therefore, OP or angiotensin converting enzyme (ACE) for the cardiovascular system and, therefore, CAD. The investigation of gene polymorphisms in various pathological conditions typical of postmenopause offer an explanation not only of their genetic inheritance but also of their co-segregation in given individuals. In this view, it may be possible to identify a common set of genes whose variants contribute to a common genetic background for these different disorders. Ideal candidates appear genes of the estrogen response cascade [i.e. estrogen receptor (ERs), enzymes involved in estrogen metabolism or co-activators and co-inhibitors]. All together this information may represent the basis both for future recognition of individuals at risk and for the pharmacogenetic driving of drug responsiveness.