Genetic determinants of bone mineral content at the spine and radius: a twin study

Epidemiology of osteoporosis

This review has shown that osteoporosis is a major public health problem because of its association with fracture. It is now possible to predict future risk of fracture by measuring BMD with noninvasive techniques. The relation between BMD and fracture is comparable to that between blood pressure and stroke such that fracture risk can be assessed from a definition of osteoporosis using bone mass and past history of fracture. Because some of the risk factors for peak bone mass, involutional bone loss, and fracture are now characterized, coupled with innovative agents capable of retarding bone loss, it is becoming possible to generate preventive strategies, for the entire population as well as for those at highest risk.

Sex steroids and bone

Sex steroids are essential for skeletal development and the maintenance of bone health throughout adult life, and estrogen deficiency at menopause is a major pathogenetic factor in the development of osteoporosis in postmenopausal women. The mechanisms by which the skeletal effects of sex steroids are mediated remain incompletely understood, but in recent years there have been considerable advances in our knowledge of how estrogens and, to a lesser extent androgens, influence bone modeling and remodeling in health and disease. New insights into estrogen receptor structure and function, recent discoveries about the development and activity of osteoclasts, and lessons learned from human and animal genetic mutations have all contributed to increased understanding of the skeletal effects of estrogen, both in males and females. Studies of untreated and treated osteoporosis in postmenopausal women have also contributed to this knowledge and have provided unequivocal evidence for the potential of high-dose estrogen therapy to have anabolic skeletal effects. The development of selective estrogen receptor modulators has provided a new approach to the prevention of osteoporosis and other major diseases of menopause and has implications for the therapeutic use of other steroid hormones, including androgens. Further elucidation of the mechanisms by which sex steroids affect bone thus has the potential to improve the clinical management not only of osteoporosis, both in men and women, but also of a number of other diseases related to sex hormone status.

Determination of bone mineral density of the hip and spine in human pedigrees by genetic and life-style factors

In 40 human pedigrees with 563 subjects, we evaluated the contribution of genetic and life-style factors (exercise, smoking, and alcohol consumption) and the interactions between non-genetic factors in determining bone mineral density (BMD) of the hip and spine. In our analysis, we adjusted for age, weight, height, menopausal status in females, life-style factors, and the significant interactions among these factors. For the spine and hip BMD, heritabilities (h(2)) (+/- SE) were, respectively, 0.68 (0.21) and 0.86 (0.28) in males and 0.64 (0.13) and 0.67 (0.14) in females. Exercise had significant beneficial effects for male spine BMD and female hip BMD. Alcohol consumption experienced in our sample had significant beneficial effects on hip BMD in both sexes. Although the main effect of smoking was not significant, there were significant interaction effects between smoking and other important factors (e.g., exercise, weight, alcohol consumption). For example, for female spine BMD, exercise had significant beneficial effects in smokers; however, its effect in non-smokers was non-significant. This result indicates that exercise may reduce deleterious effects of smoking (if any) on BMD, but may have minor effects in increasing BMD in non-smokers. The various interaction effects among risk factors explicitly revealed here for the first time indicate that the detailed effects and direction of individual risk factors may depend on the presence and magnitude of other factors. Weight invariably affected BMD of the hip and spine in both sexes. Age effects were significant for hip BMD, but not for male spine BMD.

Genetic determination of Colles' fracture and differential bone mass in women with and without Colles' fracture

Osteoporotic fractures (OFs) are a major public health problem. Direct evidence of the importance and, particularly, the magnitude of genetic determination of OF per se is essentially nonexistent. Colles' fractures (CFs) are a common type of OF. In a metropolitan white female population in the midwestern United States, we found significant genetic determination of CF. The prevalence (K) of CF is, respectively, 11.8% (+/- SE 0.7%) in 2471 proband women aged 65.55 years (0.21), 4.4% (0.3%) in 3803 sisters of the probands, and 14.6% (0.7%) in their mothers. The recurrence risk (K0), the probability that a woman will suffer CF if her mother has suffered CF is 0.155 (0.017). The recurrence risk (Ks), the probability that a sister of a proband woman will suffer CF given that her proband sister has suffered CF is 0.084 (0.012). The relative risk lambda (the ratio of the recurrence risk to K), which measures the degree of genetic determination of complex diseases such as CF, is 1.312 (0.145; lambda 0) for a woman with an affected mother and 1.885 (0.276; lambda s) for a woman with an affected sister. A lambda-value significantly greater than 1.0 indicates genetic determination of CF. The terms lambda 0 and lambda s are related to the genetic variances of CF. These parameters translate into a significant and moderately high heritability (0.254 [0.118]) for CF. These parameters were estimated by a maximum likelihood method that we developed, which provides a general tool for characterizing genetic determination of complex diseases. In addition, we found that women without CF had significantly higher bone mass (adjusted for important covariates such as age, weight, etc.) than women with CF.

Sib pair linkage and association studies between bone mineral density and the interleukin-6 gene locus

A major determinant of the risk for osteoporosis in later life is bone mineral density (BMD) attained during early adulthood. Bone mineral density is a complex trait that, presumably, is influenced by multiple genes. Interleukin-6 (IL-6) is an attractive candidate gene for osteoporosis susceptibility, because it has effects on bone cells and has been implicated in the pathogenesis of osteoporosis. Furthermore, previous investigators have identified an association between a 3' UTR polymorphism of the IL-6 gene and BMD. In this study, we searched for linkage and association between this IL-6 gene polymorphism and peak BMD in a large population (812 individuals) of healthy premenopausal sibpairs. Although previous investigators identified only 6 IL-6 alleles, we identified 17 alleles by modifying electrophoretic conditions and evaluating a very large population. We found no evidence for either linkage or association between the IL-6 gene locus and BMD of the spine or hip in either Caucasians or African Americans.

A familial risk profile for osteoporosis

PURPOSE

To describe genetic epidemiologic aspects of osteoporosis.

METHODS

69 patients with osteoporosis were interviewed regarding personal and family histories of osteoporosis and related fractures. Family history information was obtained on 421 first degree and 748 second degree relatives.

RESULTS

45% of cases reported a family history of osteoporosis. Familial cases were characterized neither by an earlier age of diagnosis nor by a greater degree of phenotypic severity. Empiric risks for osteoporosis were highest for mothers, 33%, and were 19% for sisters.

CONCLUSION

These results provide an initial genetic epidemiologic profile for osteoporosis and information useful for genetic counseling.

The association between heel ultrasound and hormone replacement therapy is modulated by a two-locus vitamin D and estrogen receptor genotype

Evidence supports the role of estrogen deprivation in the process of bone remodeling and increased risk of fracture in postmenopausal women but little is known about the genetic basis of individual differences in response to therapy. In a cross-sectional study, 425 ambulatory postmenopausal French-Canadian women from Quebec (age range, 42-85 years old) were genotyped for a common Bsm I polymorphism at the vitamin D receptor (VDR) gene as well as a Pvu II polymorphism in the estrogen receptor (ESR1) gene. Heel ultrasound was determined by right calcaneal quantitative ultrasound (QUS) and results were expressed as an age-and-weight-adjusted stiffness index (heel SI z score). Our aim was to investigate the interaction between hormone-replacement therapy (HRT) and receptor genotypes in an effect on heel SI. Notably, a two-locus genotype (VDR-bb/ESR-PP) present in 9.5% of women was responsible for over 30% of the total HRT-related heel SI difference in the whole sample. Women bearing this combined VDR/ESR1 genotype who received HRT for more than 5 years had a 21% (1.25 SD) greater heel SI (p = 0.002) than those bearing the same genotype but who received HRT for <5 years. This may translate into a 2- to 3-fold difference in the risk of fracture. Although follow-up studies are needed, our findings suggest that QUS of the heel in postmenopausal women taking HRT is affected by variation in VDR and ESR1 loci, jointly.

Genetic epidemiological approaches to the search for osteoporosis genes

Important progress has been made in the identification of specific environmental factors and estimation of hereditary components in bone density, quantitative ultrasound (QUS), and bone turnover indices. By contrast, the search for specific genes that regulate bone mass has progressed rather slowly, and the results are more difficult to interpret and reproduce. This article reviews the genetics of osteoporosis and problems plaguing genetic research. It is argued that the search for genes involved in the expression of osteoporotic phenotypes should be based on linkage studies in relatively homogeneous populations. Strategies for increasing the power of studies, such as making use of information from extended pedigrees and multivariate analysis, are discussed. With the advent of a comprehensive human genetic linkage map, a complete identification of genes for osteoporosis appears feasible. Understanding the genetic mechanisms and their interactions with environmental factors should allow more focused and cost-effective osteoporosis prevention and treatment strategies.

The genetics of osteoporosis: 'complexities and difficulties'

Osteoporosis is characterized by a decrease in bone mass as well as a deterioration of the bone architecture resulting in an increased risk of fracture. Although the disease is multifactorial, twin studies have shown that genetic factors account for up to 80% of the variance in bone mineral density, the best known predictor of the risk of osteoporosis. Some loci, such as the vitamin D and estrogen receptor genes, as well as the collagen type Ialpha1 locus, are promising genetic determinants of bone mass, and possibly other bone phenotypes, but this is controversial and the molecular basis of osteoporosis remains largely undefined. Considering that the effect of each candidate gene is expected to be modest, discrepancies between allelic association studies may have arisen because different populations carry different genetic backgrounds and exposure to environmental factors. Also, we realize the importance of gene-gene as well as gene-environment interactions as significant determinants of bone density and risk of osteoporosis. The use of new tools such as small nucleotide polymorphism maps now allows the possibility to perform allelic association studies in the context of whole-genome search. However, specific study design strategies in large epidemiological studies as well as the best statistical approach will need to be established. We may expect the development of population-specific at-risk profiles for osteoporosis that would include genetic and environmental factors, as well as their interactions. This should eventually lead to better prevention strategies and more adapted therapies against osteoporosis.

Apolipoprotein E gene polymorphism and bone loss: estrogen status modifies the influence of apolipoprotein E on bone loss

The identification of genes that contribute to bone mineral density (BMD) and bone loss has widespread implications for the understanding and prevention of osteoporosis. The objective of this study was to examine the relationship between the presence and absence of the apolipoprotein E*4 (APOE*4) allele and both BMD and annualized percentage rate of change in BMD at the lumbar spine and hip in a population of 392 healthy, pre-, peri-, and postmenopausal white women participating in the Women's Healthy Lifestyle Project. APOE genotype was analyzed by restriction enzyme analysis from genomic DNA. BMD at the lumbar spine and hip was measured at baseline and after a mean of 2.5 years using dual-energy X-ray absorptiometry (DXA). In premenopausal women, there were no significant differences in BMD or in the annualized percentage rate of change in BMD at the spine or hip when comparing women with and without the APOE*4 allele. In contrast, spine bone loss was significantly greater in peri- and postmenopausal women having an APOE*4 allele than in women without this allele (-1.75 + 1.5% per year vs. -0.98 +/- 1.4% per year, respectively, p = 0.018). Among peri- and postmenopausal women currently using hormone replacement therapy (HRT), there were no differences in the annualized percentage rate of change in spine BMD; whereas, among non-HRT users, there was a 2-fold higher rate of spine bone loss in women with an APOE*4 allele compared with women without this allele (-2.31 +/- 1.5% per year vs. -1.27 +/- 1.3% per year, respectively, p = 0.033; APOE*4 x HRT interaction, p = 0.076). In conclusion, this study shows the importance of APOE*4 allele in spine bone loss in peri- and postmenopausal women and, more importantly, it provides evidence for a genetic and lifestyle interaction in modulating spine bone loss.

Sibling pair linkage and association studies between bone mineral density and the insulin-like growth factor I gene locus

A major determinant of the risk for osteoporosis in later life is bone mineral density (BMD) attained during early adulthood. BMD is a complex trait that presumably is influenced by multiple genes. Insulin-like growth factor I (IGF-I) is an attractive candidate gene for osteoporosis susceptibility, because IGF-I has marked effects on bone cells and has been implicated in the pathogenesis of osteoporosis. The IGF-I gene contains a microsatellite repeat polymorphism approximately 1 kb upstream from the IGF-I gene transcription start site, and previous investigators have found a higher prevalence of the 192/192 genotype of this polymorphism among men with idiopathic osteoporosis compared to controls. In this study we used this IGF-I polymorphism to test for an association between this polymorphism and BMD in our large population of premenopausal women (1 sister randomly chosen from 292 Caucasian and 71 African-American families). We also used this polymorphism to detect linkage to BMD elsewhere in the IGF-I gene or in a nearby gene using sibling pair linkage analysis in healthy premenopausal sister pairs (542 sibling pairs: 418 Caucasian and 124 African-American). Neither test provided any evidence of linkage or association between the IGF-I gene locus and spine or femoral neck BMD in Caucasians or African-Americans.

Lack of association between estrogen receptor genotypes and bone mineral density, fracture history, or muscle strength in elderly women

The PvuII polymorphism of the estrogen receptor (ESR) gene and its relation to bone mineral density (BMD), fracture history, and muscle strength was studied in 313 postmenopausal (76 +/- 5 years) women of Caucasian origin, of whom 142 had suffered from a fragility fracture after the age of 50 years (14 with fracture of the hip, 38 of the spine, 45 of the wrist, and 85 of other bones). The ESR genotype distribution was similar in women with and without a history of fragility fracture (PP 21%, Pp 43%, pp 36% compared with PP 18%, Pp 47%, pp 35%). We did not find a correlation between the ESR genotypes and BMD at the lumbar spine, the femoral neck, or the proximal forearm. No association was found with grip or quadriceps strength. We further evaluated the relationship between the vitamin D receptor (VDR) and ESR haplotypes and BMD in a random subgroup of 270 elderly women. No differences were found in women with the BBpp versus the bbPP haplotype in the femoral neck (mean difference +/- SD, in Bbpp compared with bbPP groups: -0.05 +/- 0.15 g/cm2), the spine (0.01 +/- 0.13 g/cm2), or the forearm (0.04 +/- 0.08 g/cm2). The significant association of quadriceps strength with VDR genotypes (25% lower in BB compared with bb genotype, p < 0.05) was not influenced by ESR haplotypes. We conclude that in elderly Caucasian women the PvuII ESR polymorphism is not associated with osteoporosis, fracture history, nor muscle strength and does not influence the association of bone density and muscle strength with polymorphism of the VDR.

Vitamin-D receptor genotype does not predict bone mineral density, bone turnover, and growth in prepubertal children

We examined whether the polymorphism for BsmI restriction enzyme in the vitamin-D receptor (VDR) gene influenced radial (distal third) and lumbar (L2-L4) bone mineral density (BMD), phospho-calcium metabolism (calcium, phosphate, intact parathyroid hormone, 25-hydroxyvitamin D, and 1,25-dihydroxyvitamin D), biochemical markers of bone formation (osteocalcin and carboxy-terminal propeptide of type-I procollagen) and bone resorption (carboxy-terminal telopeptide of type-I collagen and urinary cross-linked N-telopeptides of type I collagen), insulin-like growth factor I and insulin-like growth factor-binding protein 3, and growth in 209 healthy prepubertal children (112 males and 97 females) aged 7.1-10.0 years. Genotype frequencies were BB 19%, Bb 46%, and bb 35% in the pooled group of children. Clinical findings, dietary calcium intake, calcium density, and physical activity rate were not different (p NS) among the VDR genotypes. Radial BMD, lumbar BMDarea and lumbar BMD adjusted for the apparent bone volume (BMDvolume), and all the biochemical parameters did not differ (p NS) in relation to the VDR genotype. In conclusion, our data show that polymorphism for BsmI restriction enzyme in the VDR gene is not associated with radial and lumbar BMD, parameters of phospho-calcium metabolism and bone turnover, growth hormone-dependent growth factors, and growth in prepubertal children.

Genetic determinants of bone mass

A genetic contribution to bone mass determination was first described in the early 70s. Elucidation of gene contribution to this has since been attempted through studies analyzing associations between bone mass acquisition and/or maintenance and polymorphic variations of several genes. The first to be described was the vitamin D receptor gene (VDR), initially claimed to contribute to almost 75% of the genetic variation in bone mineral density (BMD) in twin and general population studies. Not all of the studies published to date conclude that a clear relationship exists between polymorphic VDR alleles and BMD, and the molecular basis for the VDR gene polymorphisms influence on bone mineralization has not yet been clarified. Since then, other genes with a significant role in bone metabolism such as estradiol receptor, collagen type 1alpha1, TGF-beta1, interleukin-6, calcitonin receptor, alpha2-HS-glycoprotein, osteocalcin, calcium-sensing receptor, interleukin-1 receptor antagonist, beta3-adrenergic receptor, apolipoprotein E, PTH, IGF-I and glucocorticoid receptor have been analyzed. Some polymorphic variations in these genes have been associated in some works with significant differences in BMD, with even more significant contributions when associations of different gene polymorphisms were analyzed. Again, the molecular basis for the contribution of these alleles to bone mass determination has not yet been described. A different approach has been attempted by linkage analysis of loci involved in bone density in pedigrees with low BMD using BMD as a quantitative trait. Recent results do not confirm, in these families, any association with any of the previously reported genes, but rather with other as yet unidentified genes. The genetic contribution to mild variations in the general population, as a result of environmental and endogenous individual influences, probably differs completely from that providing a pathologic BMD.

Association between a family history of fractures and bone mineral density in early postmenopausal women

The aim of this analysis was to measure the strength of the association between a family history of fractures and bone mineral density (BMD), and to determine what definition of family fracture history best predicts BMD. Five hundred and eighty postmenopausal women aged 45-59 at recruitment completed a risk factor questionnaire. Women were asked to recall details of fractures sustained by any female relative. BMD measurements taken at five sites were used. The data were analysed using linear regression, adjusting for age. Two hundred and ninety-seven (52.8%) women reported a family history of fractures, and they had a significantly lower BMD at two of the sites measured (p < 0.05). The associations with BMD were most significant when only counting fractures that occurred in the subject's mother or a sister as a result of low trauma, with no restrictions made on age at the time of fracture and site of fracture (p < 0.01 at three sites; 0.01 < p < 0.05 at two sites). Women with a family history according to this definition had a 4.6% reduction in BMD at the femoral neck. When T scores were used to categorize women as either osteopenic/osteoporotic (T < -1) or normal at the femoral neck, the sensitivity of using this definition was 39% and the specificity was 74%. The small group of women that reported a low-trauma hip fracture in a mother or sister (n = 23) had a mean femoral neck BMD which was 8.9% lower than that of the remainder of the sample, although this difference was less statistically significant than when low trauma fractures at any site were counted. Of these 23 women, 70% were osteopenic or osteoporotic, compared with 57% of those reporting a low-trauma fracture at any site and 47% of the sample as a whole. The sensitivity of this definition, however, was low (6%). From these analyses it can be concluded that the definition of family fracture history that best predicts BMD in postmenopausal women is a fracture at any age in a mother or sister resulting from low trauma, although the sensitivity and specificity of using a family history of fractures by itself to screen for low BMD were poor.

Determinants of peak bone mass: clinical and genetic analyses in a young female Canadian cohort

Peak bone mass has been shown to be a significant predictor of risk for osteoporosis. Previous studies have demonstrated that skeletal mass accumulation is under strong genetic control, and efforts have been made to identify candidate loci. Determinants of peak bone mass also include diet, physical activity, hormonal status, and other clinical factors. The overall contribution of these factors, genetic and nongenetic, and their interaction in determining peak bone density status have not been delineated. Six hundred and seventy-seven healthy unrelated Caucasian women ages 18-35 years were assessed. A detailed, standardized interview was conducted to evaluate lifestyle factors, menstrual and reproductive history, medical conditions, medication use, and family history of osteoporosis. Bone mineral density (BMD) was measured at the lumbar spine (L2-L4) and the femoral neck (hip) using dual-energy X-ray absorptiometry. Genotyping of the vitamin D receptor (VDR) locus at three polymorphic sites (BsmI, ApaI, and TaqI) was performed. In bivariate analyses, BMD at the lumbar spine and hip was positively correlated with weight, height, body mass index (BMI), and level of physical activity, both now and during adolescence, but negatively correlated with a family history of osteoporosis. Hip, but not spine BMD, correlated positively with dietary intake of calcium, and negatively with amenorrhea of more than 3 months, with caffeine intake, and with age. Spine, but not hip BMD, correlated positively with age and with number of pregnancies. VDR haplotype demonstrated significant associations with BMD at the hip, level of physical activity currently, and BMI. In multivariate analysis, independent predictors of greater BMD (at the hip or spine) were: age (younger for the hip, older for the spine), greater body weight, greater height (hip only), higher level of physical activity now and during adolescence, no family history of osteoporosis, and VDR genotype (hip only). Weight, age, level of physical activity, and family history are independent predictors of peak BMD. Of these factors, weight accounts for over half the explained variability in BMD. VDR alleles are significant independent predictors of peak femoral neck, but not lumbar spine BMD, even after adjusting for family history of osteoporosis, weight, age, and exercise. However, the overall contribution of this genetic determinant is modest. Taken together, these factors explained approximately 17% and 21% of the variability in peak spine and hip BMD, respectively, in our cohort. Future research should be aimed at further evaluation of genetic determinants of BMD. Most importantly, understanding the critical interactive nature between genes and the environment will facilitate development of targeted strategies directed at modifying lifestyle factors as well as earlier intervention in the most susceptible individuals.

Lack of an intronic Sp1 binding-site polymorphism at the collagen type I alpha1 gene in healthy Korean women

Osteoporosis is a disease that is strongly genetically influenced. However, the genes responsible for the disease are poorly defined. Recent data show that a G-T transition polymorphism of the Sp1 binding site at the collagen type I alpha1 gene (Sp1 polymorphism) is associated significantly with bone mineral density (BMD) and osteoporotic fracture in British women. To establish the association between the Sp1 genotypes and BMD in Korean women, we examined 200 healthy postmenopausal women of Korean ethnicity, ranging in age from 44 to 66 years (mean+/-SD: 54.7+/-5.3 years). PCR amplification using the same primers as those used previously, with enzyme digestion, revealed no restriction site in our samples. We also performed a single-strand conformational polymorphism (SSCP) analysis in 100 of the 200 samples and could not find any polymorphic sites in the PCR amplification region. Based on our study, the Sp1 polymorphism at the type I collagen alpha1 gene was not found in Korean women. Therefore, we suggest that the Sp1 polymorphism at the type I collagen alpha1 gene is absent or rare in Korean women. Based on the present findings, this polymorphism does not seem to be responsible for the entire genetic contribution to BMD.

Genetic determination of variation and covariation of peak bone mass at the hip and spine

The likelihood of low trauma fracture in the elderly is highly predictable by peak bone mass (PBM) at age approximately 25-50 yr. We estimated the magnitude of genetic determination of the variation and covariation of PBM of the spine and hip (adjusted by age, gender, and ethnicity) in 47 independent healthy full-sib pairs and 27 healthy mother-offspring pairs. For the spine and hip, the narrow-sense heritabilities (h(2)) (mean +/- SE) were 0.76 +/- 0.34 and 0.84 +/- 0.36, respectively, when estimated from full sibs, and 0.86 +/- 0.38 and 0.84 +/- 0.39, respectively, when estimated from parent-offspring. Some genetic loci underlying PBM variation at the hip and spine are the same or closely linked, as is reflected by the high genetic correlation of 0.95 +/- 0.05 between them when estimated from full sibs, and 0.57 +/- 0.27 when estimated from parent-offspring, respectively. Generally, common familial environmental effects shared by relatives may bias these estimates. However, these effects may be small, since our results reported herein and those in other earlier studies indicate that common familial environmental effects are probably negligible in causing similarity of bone mass among family members. The correlation of bone mass among randomly sampled couples living in the same household is small and nonsignificant as measured either by densitometry at the radius and ulna or by quantitative ultrasound at the patella. The problem of shared environmental effects notwithstanding, we conclude that much of the PBM variation and covariation at the hip and spine is determined genetically.

The genetics of osteoporosis: vitamin D receptor polymorphisms

Osteoporosis is a metabolic bone disease characterized by low bone mass and deterioration of bone tissue that leads to bone fragility and an increase in fracture risk. It is a disease with a complex etiology that includes genetic and environmental contributors. Environmental factors that influence bone density include dietary factors-such as intakes of calcium, alcohol, and caffeine-and lifestyle factors-such as exercise and smoking. Ethnic differences in the propensity to nontraumatic bone fracture suggest that genetic factors are important. Recently, common allelic variations in he vitamin D receptor gene have been found to be associated with bone mineral density in racially diverse population groups, as well as in prepubertal girls, young adult and postmenopausal women, and men. However, many studies have not been able to find this association. Additional approaches, such as sib-pair analysis, will probably be necessary in the future to identify the important determinants of osteoporosis.

Genetic and environmental contributions to the association between quantitative ultrasound and bone mineral density measurements: a twin study

This study was designed to assess the relative contributions of genetic and environmental factors to the variation and covariation of quantitative ultrasound (QUS) measurements and their relationships to bone mineral density (BMD). Forty-nine monozygotic (MZ) and 44 dizygotic (DZ) female twins between 20 and 83 years of age (53 +/- 13 years, mean +/- SD) were studied. Digital (phalangeal) QUS (speed of sound [SOS]) and calcaneal QUS (broadband ultrasound attenuation [BUA] and velocity of sound [VOS]) were measured using a DBM Sonic 1200 ultrasound densitometer and a CUBA ultrasound densitometer, respectively. Femoral neck (FN), lumbar spine (LS), and total body (TB) BMD were measured using dual-energy X-ray absorptiometry. Familial resemblance and hence heritability (proportion of variance of a trait attributable to genetic factors) were assessed by analysis of variance, univariate, and multivariate model-fitting genetic analyses. In both QUS and BMD parameters, MZ twins were more alike than DZ pairs. Estimates of heritability for age- and weight-adjusted BUA, VOS, and SOS were 0.74, 0.55, and 0.82, respectively. Corresponding indices of heritability for LS, FN, and TB BMD were 0.79, 0.77, and 0.82, respectively. In cross-sectional analysis, both BUA and SOS, but not VOS, were independently associated with BMD measurements. However, analysis based on intrapair differences suggested that only BUA was related to BMD. Bivariate genetic analysis indicated that the genetic correlations between BUA and BMD ranged between 0.43 and 0.51 (p < 0.001), whereas the environmental correlations ranged between 0.20 and 0.28 (p < 0.01). While the genetic correlations within QUS and BMD measurements were significant, factor analysis indicates that common genes affect BMD at different sites. Also, individual QUS measurements appear to be influenced by some common sets of genes rather than by environmental factors. Significant environmental correlations were only found for BMD measurements and ranged between 0.50 and 0.65 (p < 0.001). These data suggest that QUS and BMD measurements are highly heritable traits. While it appears that there is a common set of genes influencing both QUS and BMD measurements, specific genes yet to be identified appear to have greater effects than that of shared genes in each trait.

Recombinant human growth hormone as potential therapy for osteoporosis

Growth hormone (GH) directly stimulates proliferation and differentiated functions of cultured bone cells. In addition, temporal relationships between decreased function of the GH/IGF-1 axis and age-related bone loss have prompted some investigators to hypothesize that these two phenomena are causally related, and to test this hypothesis by evaluating the effects of GH administration on bone turnover and mineral density in older men and women. Although these studies show clearly that GH initiates bone remodelling activity, changes in bone mass have not been impressive, even when GH was given in combination with anti-resorptive therapy. Thus, it appears very unlikely that GH will offer a clinically useful means to restore skeletal deficits in patients with osteoporosis.

Genetic and environmental factors affecting bone mineral density in large families

This study assessed whether relatives with low bone mineral density (BMD) could be identified in five large families using historical, biochemical, and genetic markers for osteoporosis. Fifty of 65 relatives had their bone density and bone turnover markers measured, together with an assessment of their risk factors for osteoporosis. Only 33% (5/15) of siblings, 50% (6/12) of children and 43% (10/23) of nephews and nieces had entirely normal BMD. There was no difference in life-style risk factors for osteoporosis, history of previous fractures or body mass index between normal subjects and those with osteopenia or osteoporosis. Osteopenic individuals had a significantly higher than normal osteocalcin value. Within families, there was no clear association between BMD and any of the genetic markers (vitamin D receptor gene polymorphisms, COL 1A1 and COL 1A2 polymorphisms of the collagen gene), either alone or in combination. The addition of genetic markers to the other risk factors for low BMD did not improve the prediction of BMD. In conclusion, we suggest that the presence of osteoporosis in a first degree relative should be one of the clinical indications for bone density measurement as the individuals at risk would not be picked up by other methods.

Diagnostic sensitivity of peripheral quantitative computed tomography measurements at ultradistal and proximal radius in postmenopausal women

Peripheral quantitative computed tomography (pQCT) is a bone densitometry technique that is able to provide real volumetric bone density values not only of the total but also of trabecular and cortical bone separately. Normal reference curves were constructed with cross-sectional data obtained in 275 postmenopausal women (50-85 years), measured at 4% of the ulnar length (ultradistal region), and data for total, trabecular, and cortical bone density were obtained. In these postmenopausal subjects, continuously significant (p < 0.0001) age-dependent declines in bone density of 1.14%, 1.1%, and 0.57% for total, trabecular, and cortical bone, respectively, were observed while similar declines of 0.9%, 0.9%, and 0.4% per year since menopause, respectively, were found. The estimated mechanical stability index also showed linear dependencies with decreases of 0.84%/year and 0.6%/year since menopause (p < 0.0001). A more proximal acquisition at 15% of the ulnar length, an almost pure cortical region, resulted in linear declines of 0.41%/year and 0.27%/year (p < 0.0001) for the cortical bone and the mechanical stability index with significant changes of -0.27% and -0.23% per year, respectively, since menopause. Covariance analysis showed similar age dependencies of the different bone indices obtained in both regions of interest except for the stability index. A significant size adaptation of the bone with age was also observed, which was seen in the relationships of the trabecular and cortical bone areas to age and to bone density. Diagnostic sensitivity of all parameters for established osteoporosis was assessed by receiver operating characteristic (ROC) curves, comparing 99 patients with at least one fracture to the reference population. The area under these curves was highest in the ultradistal pure trabecular density of the radius (75%), followed by stability index (72%) and the area of cortical bone (65%) of the proximal site. No distinguishing power was seen for the cortical bone density values obtained in either the ultradistal (51%) or proximal radius (52%).

Determinants of axial and peripheral bone mass in Chinese adolescents

OBJECTIVE

To determine the relation of puberty, physical activity, physical fitness, and calcium intake with bone mineral content (BMC) of the distal radius, and on bone mineral density (BMD) of the L2 to L4 vertebrae in a group of healthy Chinese adolescents.

DESIGN

Cross sectional survey.

SUBJECTS

A group of 179 healthy Chinese adolescents (92 boys and 87 girls) aged 12 to 13 years enrolled in the first year of the Tii Junior High School in Shatin, Hong Kong. Ninety four of the pupils enrolled were in the physical education major class (PE), and the other 85 were in the art major class (ARTS).

MAIN OUTCOME MEASURES

Correlation of BMC of the distal radius and BMD of the L2 to L4 vertebrae with level of physical activity, physical fitness (isometric and isokinetic), muscle strength of the upper and lower limb, and calcium intake.

RESULTS

BMC of the distal radius and BMD of the L2 to L4 vertebrae were significantly positively correlated. Univariate and regression analysis showed that age, pubertal staging, physical fitness, and muscle strength were significantly associated with bone mass in a positive way. Calcium intake and type of sport practised did not exert a significant influence on BMC of the distal radius and BMD of the L2 to L4 vertebrae in boys. The results for the BMD of the L2 to L4 vertebrae were similar in girls and boys; however, in girls, the BMC of the distal radius had a negative correlation with calcium intake. Physical fitness was a significant positive predictor of BMD of the L2 to L4 vertebrae.

CONCLUSIONS

Among Chinese adolescents bone mass was positively influenced by certain measures of physical fitness as well as by age, weight, and pubertal stage.

Morphometric skeletal traits, femoral measurements, and bone mineral deposition in mice with agonistic selection for body conformation

Morphometric skeletal traits, femoral histomorphometry, and bone mineral deposition were investigated in two lines of mice (CBi+ and CBi-) divergently selected for body conformation (CBi+: high body weight, long tail; CBi-: low body weight, short tail) and in the unselected control line CBi. Linear morphometric measurements, absolute and relative skeletal weights, absolute and relative femoral weights, and total biomass sustained per unit of total or tail-less skeletal weight were increased in CBi+ mice in comparison with controls. This greater biomass implies a greater mechanical demand that is satisfied by a heavier skeleton. Looking specifically to the femur, CBi+ mice had heavier bones, both absolute and relative, with a greater diameter and a greater cortical thickness, resulting in a greater cortex/diameter ratio than controls. Although morphometric measurement and absolute skeletal weight were lower in CBi- than in CBi mice, the relative skeleton weight and the biomass sustained per unit of skeletal weight were not modified in the downward selection line when compared with controls. Therefore, CBi- mice did not exhibit a greater mechanical demand as CBi+ mice did. These results led us to consider at least three main aspects: bone length growth; cortical thickness/bone diameter ratio; and bone calcification. The long bones appeared to have a genetically determined predisposition to achieve a given length, which, however, could be modified by artificial selection. Cortical thickness would be directly related to the biomass sustained. This variable increased in CBi+ mice, a genotype that supports a greater biomass than controls, and did not change in CBi- mice, which sustained the same biomass as CBi. The pattern of mineral deposition did not accompany the functional demand because it was higher in CBi- than in CBi+; however, as artificial selection separately affected bone material quality and bone architectural design, these genotypes could express architectural modifications that override any change in bone material quality.

Genetics, calcium intake and osteoporosis

Genetic factors explain a high proportion of the age-specific differences in bone density, size and turnover. The potential for interaction between hormonal, diet and lifestyle factors is likely to be important. Common allelic variation in the VDR is an example of normal gene variants altering Ca homoeostasis, with effects on body and bone size as well as bone density. The VDR findings suggesting interactions between genetic and nutritional factors are an important target for future research. These studies are complicated by the potential for effects of gene-gene interactions and of undefined environmental factors. These problems notwithstanding, considerations of environmental and nutritional contributions, such as Ca intake and vitamin D status, will be critical in interpreting these genetic pathways and in 'personalizing' nutritional recommendations.

Collagen Ialpha1 Sp1 polymorphism, bone mass, and bone turnover in healthy French premenopausal women: the OFELY study

Bone mineral density (BMD) is under strong genetic control. Recent work has suggested that a polymorphism affecting an Sp1 binding site in the collagen I (COLI) A1 gene is associated with BMD and vertebral fracture in postmenopausal women. We analyzed this polymorphism in relation to BMD and bone turnover in 220 healthy premenopausal women aged 31-57 years. There were 61% SS homozygotes, 35% Ss heterozygotes, and 4% ss homozygotes, genotype frequencies similar to those previously reported in other Caucasian populations. Women in the three genotype groups were matched for age, body weight, physical activity, smoking habits, and oral contraceptive use, but height was greatest in the SS group and lowest in the ss group (p = 0.03). Between-group comparisons by analysis of variance (ANOVA) showed that COLI A1 genotype was significantly associated with spine BMD (p = 0.05), total body BMD (p = 0.046), and total body bone mineral content (BMC) (p = 0.02), but the differences between extreme genotypes were small (4, 5, and 10%, for spine BMD, total body BMD, and total body BMC, respectively). After adjustment for height, the differences between genotypes decreased and were no longer significant by ANOVA (p = 0.08, 0.17, and 0.33 for spine BMD, total body BMD, and total body BMC). Furthermore, no significant difference between genotypes was observed for femoral neck, trochanter, Ward's triangle, or forearm BMD. COLI A1 genotype was associated with serum C-terminal extension propeptide of type I collagen (p = 0.04), with lowest levels in ss individuals, but not with any other marker of bone formation (osteocalcin, alkaline phosphatase, and type I collagen N-terminal extension propeptide) or bone resorption (urinary excretion of type I collagen C and N telopeptide breakdown products). The COLI A1 Sp1 polymorphism is associated with height, peak total body BMD and BMC, and spine BMD. The genotype-specific differences account for only a small proportion of variance in BMD at these sites and are not significant after adjustment for height, suggesting that part of the effect on bone mass may be due to differences in body size. Our data support the view that COLI A1 may be a candidate gene for regulation of bone mass, but our results must be treated with caution, in view of the small number of ss individuals, and will require confirmation in larger studies.

Lack of correlation of free deoxypyridinoline excretion with Taq1 restriction length polymorphisms in the vitamin D receptor gene in males

An association between allelic variants in the vitamin D receptor gene and bone mineral density has been previously described. A bimodal variation in the rate of bone resorption (as measured by urinary deoxypyridinoline excretion rate) has also been reported. We have recruited male volunteers, to minimise variation associated with ovarian function, to investigate a possible connection between these observations. Allelic variants in the vitamin D receptor gene were identified as Taq1 restriction fragment length polymorphisms. The ratio of variants TT:Tt:tt occurred with a frequency of 34%:47%:17%. Excretion rates of urinary free deoxypyridinoline, measured by immunoassay, were compared in age-matched males from each genetic group. There were no significant differences based on the paired Student's t-test. Excretion rates declined with age (P = 0.04) and the best fit model fits the same regression line to each group. Genetic variation in the vitamin D receptor is not linked with differences in bone resorption rates.

HLA-A*24-B*07-DRB1*01 haplotype implicated with genetic disposition of peak bone mass in healthy young Japanese women

HLA exhibits the most extensive polymorphism of any of the known human genes and is known as a genetic marker which allows genetic background of many diseases and physical phenomena. In this study, we, therefore, tried to investigate the regulation of HLA polymorphism and peak bone mass (PBM) in order to elucidate the genetic backgrounds of bone metabolism in young women. Subjects were 67 healthy young Japanese women (average age: 23.6 +/- 2.6 years, Body Mass Index (BMI): 19.9 +/- 2.0 who were randomly chosen. Allelic polymorphisms in HLA class I (HLA-A and -B) and HLA-class II (DRB1) were investigated by PCR-SSOP and PCR-SSP. Vitamin D Receptor (VDR) and Estrogen Receptor (ER) gene polymorphisms were also analyzed. Lifestyle factors, such as exercise and nutrition, were examined by questionnaire. Bone mineral density was examined using with Lunar DPX-L. Subjects who possessed HLA-B*07 had a significantly lower PBM than those without B*07 (p < 0.05). All subjects were divided into 3 groups according to HLA haplotypes linked with HLA-B*07, as follows: A*24(+/-)B*07(-)DRB1*01(+/-), A*24(+)B*07(+)DRB1*01(-), and A*24(+)B*07(+)DRB*01(+). There were no significant differences between these three groups in factors that affect bone metabolism, such as age, age at menarche, BMI, calcium intake, exercise habits, VDR or ER allele frequency. The HLA-A*24-B*07-DRB1*01 haplotype had a significantly lower Z score in the lumbar spine compared with subjects without this haplotype (p < 0.05). When the Z score was divided by values higher or lower than +1 or -1, all 3 subjects whose Z score was lower than -1.0 were found to have the HLA-A*24-B*07-DRB1*01 haptotype. A significant association between HLA-A*24-B*07-DRB1*01 and Z score < -1 was found (Yate's correction chi(2) = 10.82, p = 0.001, RR = 204). In conclusion, the HLA-A*24-B*07-DRB*01 haplotype can be considered a new genetic marker implicated with low PBM in healthy young Japanese women.

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

Whether vitamin D receptor (VDR) gene polymorphisms are associated with osteoporosis is highly controversial. The relationship between VDR gene polymorphisms and bone mineral density (BMD) might, however, be modified by age-related and/or environmental factors. We studied the potential association between BMD and VDR genotypes in females from prepuberty to premenopause and prospectively investigated the interaction of VDR genotypes with dietary calcium and BMD changes during childhood. Bsm I VDR gene polymorphisms and BMD at the lumbar spine (LS) and femur (neck [FN] and midshaft [FS]) were assessed in 369 healthy Caucasian females, aged 7-56 years (143 prepubertal girls, 54 peri- and postpubertal adolescents, and 172 premenopausal adults). Femoral trochanter (FT) and distal radius BMD (metaphysis and diaphysis) were also measured in 101 of the prepubertal girls who participated in a 1-year, double-blind, randomized study of calcium supplementation (850 mg/day) versus placebo on bone mineral mass accrual. Among all females, 150 (40.7%) had bb, 167 (45.3%) Bb, and 52 (14%) BB VDR genotypes. In prepubertal and adolescent girls altogether, LS BMD (Z scores) was associated with VDR genotypes and was significantly lower in BB than in Bb or bb subjects. Trends for a similar difference were also detected at the FN level as well as on the mean BMD (Z scores) of the three sites measured (LS, FN, and FS). By contrast, no BMD differences were detectable among VDR genotypes in the adults. In 101 prospectively studied prepubertal girls, calcium supplementation significantly increased BMD at most skeletal sites, except LS. After segregation for VDR genotypes (40 bb, 47 Bb, and 14 BB), a significant calcium effect was present in Bb but not bb girls, whereas in BB girls there was a positive but nonsignificant trend for a calcium effect. Moreover, dietary calcium intake was significantly correlated with BMD changes at various independent bone sites in Bb girls but not in bb girls. In contrast, BMD gain in bb girls appeared to be higher than among the other genotypes when the dietary calcium intake was low, i.e., in the absence of calcium supplements. BMD was significantly associated with VDR gene polymorphisms only before puberty, BB girls having significantly lower BMD (Z scores) than the other genotypes. By increasing dietary calcium intake, BMD accrual was increased in Bb and possibly BB prepubertal girls, whereas bb subjects had the highest spontaneous BMD accrual and remained unaffected by calcium supplements. Taking into account complex interactions between VDR gene polymorphisms and environmental factors, including calcium intake, may thus help to understand the discordant relationships between BMD and VDR gene polymorphisms.

Vitamin D polymorphisms and calcium homeostasis: a new concept of normal gene variants and physiologic variation

The initial findings on the vitamin D receptor have opened the field of the genetics of osteoporosis to targeted genetic studies and may open the way to genome scan approaches. Interaction between genetics, the environment, and lifestyle factors will also be an important target for future research. Understanding the physiology of such gene effects will likely open the way to more specific treatments and the selection of more appropriate and effective treatment options.

Quadriceps and grip strength are related to vitamin D receptor genotype in elderly nonobese women

Osteoporotic fragility fractures are related to bone density and injury, which are both related to muscle strength. The influence of genetic factors, such as the vitamin D receptor (VDR) polymorphism on bone mineral density (BMD), is documented but still controversial, and is not known for muscle strength. In the present study, we investigated the association between the VDR BsmI polymorphism and BMD (femoral neck [FN], lumbar spine [LS], and proximal forearm [FA]) and muscle strength (quadriceps and grip strength) in 501 healthy women older than 70 years. No association was found between the VDR genotypes and BMD in elderly women. However, in nonobese women (body mass index <30 kg/cm2), the BMD in the FN was 5% higher in women with the bb BsmI genotype than in women with the BB genotype (p < 0.05). After correction for muscle strength, no association was found. A significant association between the VDR genotypes and quadriceps and grip strength was observed. In nonobese women, a 23% difference in quadriceps strength (p < 0.01) and 7% in grip strength (NS) was observed between the bb and BB genotype of the VDR. After correction for confounding factors and BMD, this association was significant for quadriceps and grip strength. These results indicate a major association of an allelic variant at the VDR locus with muscle strength in elderly nonobese women, which could explain a small association between VDR polymorphism with BMD in the femoral neck in nonobese women. No such associations were found in obese women, suggesting that factors related to obesity obscure such an association.

Estrogen receptor gene polymorphism and bone mineral density at the lumbar spine of pre- and postmenopausal women

In order to analyze the role of the estrogen receptor (ER) gene allelic polymorphisms on bone mineral density (BMD), 173 pre- and postmenopausal women were divided into four groups according to their menstrual status (group A: premenopausal women; group B: late premenopausal women; group C: postmenopausal women who had menopause for 5 years or less; and group D: postmenopausal women who had menopause for more than 5 years), and the relationship between ER gene polymorphism and lumbar spine BMD, the percent annual change in BMD and biochemical markers were studied. The restriction fragment length polymorphism (RFLPs) were represented as Xx (XbaI) and Pp (PvuII), with upper case and lower case letters signifying the absence or presence of restriction sites, respectively. In group A, the Xx genotype had significantly higher BMD (p < 0.01) than the xx genotype, but the difference was lost in groups B, C, and D. Because the percent annual change in BMD of group A was 0.052% and was not statistically different among genotypes, it is suggested that RFLP by Xba I is closely linked with peak bone mass that was attained during the subject's late thirties. In group B, serum N-region osteocalcin (N-OC) levels and the percent annual change in BMD showed a significantly larger increase than that of group A, indicating postmenopausal bone loss had commenced. Because the N-OC level of the Xx genotype was significantly higher than that of the xx genotype (p < 0.05), and the percent annual change in BMD of the Xx genotype showed a tendency to increase (p = 0.072), it is suggested that the high BMD of the Xx genotype is rapidly lost during menopausal transition. There were no significant relationships between RFLP and BMD in groups C and D, and between RFLP and BMD in groups C and D, and between RFLP by PvuII and BMD. The present study suggests that the Xx genotype is involved in accretion of BMD during young adulthood, but the effect was lost during menstrual transition.

Vitamin D receptor gene polymorphism is associated with urinary calcium excretion but not with bone mineral density in postmenopausal women

Polymorphism of vitamin D receptor (VDR) gene has been found to be associated with serum osteocalcin (OC) levels and bone mineral density (BMD) in Caucasian identical twins and unrelated postmenopausal women. Being ethnically different and living in a geographic area with adequate vitamin D status due to abundant sunshine exposure, it is unclear whether VDR gene polymorphism will affect bone mass in Thai population. In the present study, we investigated the association between VDR gene polymorphism and bone metabolism in Thai postmenopausal women. Subjects consisted of 84 postmenopausal women. Bsm I, Taq I and Apa I polymorphisms of VDR gene were determined by PCR-RFLP. B, T and A represent the absence of the corresponding restriction sites while b, t and a indicate the presence of the restriction sites. Data were expressed as mean +/- SE. Sixty-six subjects (78.6%) had bb genotype while 18 (21.4%) had Bb genotype. None of the subjects was found to have BB genotype. Taq I restriction site was in linkage disequilibrium to the Bsm I site. For Apa I polymorphism, 33 (39.3%), 42 (50.0%) and 9 (10.7%) of the subjects had aa, Aa and AA genotypes, respectively. There was no significant difference in serum intact OC levels and BMD at various skeletal sites among subjects with different genotypes. Despite the lack of difference in BMD and intact OC levels, subjects with bb genotype had higher 24-hour urinary calcium excretion than those with Bb genotype (bb, 6.1 +/- 0.3 mmol/day; Bb, 4.4 +/- 0.6 mmol/day; p < 0.05). The effect of Bsm I VDR genotype was still significant (p < 0.05) after dietary calcium intake was controlled using analysis of covariance. Despite the difference in urinary calcium levels, there was no significant difference in fractional excretion of calcium among subjects with different Bsm I-related genotypes, suggesting that the effect of the VDR gene polymorphism on urinary calcium excretion is more likely due to the effect on intestinal calcium absorption rather than renal tubular calcium reabsorption. We conclude that VDR genotype distributions in Thai postmenopausal women are different from those reported in Caucasians. VDR gene polymorphism does not appear to be associated with BMD or bone turnover in Thai postmenopausal women. However, Bsm I VDR polymorphism may have physiologic role in calcium homeostatasis by modulating intestinal calcium absorption.

Linkage of a gene causing high bone mass to human chromosome 11 (11q12-13)

The purpose of this paper is to report the linkage of a genetic locus (designated "HBM") in the human genome to a phenotype of very high spinal bone density, using a single extended pedigree. We measured spinal bone-mineral density, spinal Z(BMD), and collected blood from 22 members of this kindred. DNA was genotyped on an Applied Biosystems model 377 (ABI PRISM Linkage Mapping Sets; Perkin Elmer Applied Biosystems), by use of fluorescence-based marker sets that included 345 markers. Both two-point and multipoint linkage analyses were performed, by use of affected/unaffected and quantitative-trait models. Spinal Z(BMD) for affected individuals (N = 12) of the kindred was 5.54 +/- 1.40; and for unaffected individuals (N = 16) it was 0.41 +/- 0.81. The trait was present in affected individuals 18-86 years of age, suggesting that HBM influences peak bone mass. The only region of linkage was to a series of markers on chromosome 11 (11q12-13). The highest LOD score (5.21) obtained in two-point analysis, when a quantitative-trait model was used, was at D11S987. Multipoint analysis using a quantitative-trait model confirmed the linkage, with a LOD score of 5.74 near marker D11S987. HBM demonstrates the utility of spinal Z(BMD) as a quantitative bone phenotype that can be used for linkage analysis. Osteoporosis pseudoglioma syndrome also has been mapped to this region of chromosome 11. Identification of the causal gene for both traits will be required for determination of whether a single gene with different alleles that determine a wide range of peak bone densities exists in this region.

American College of Sports Medicine position stand. The Female Athlete Triad

The Female Athlete Triad is a syndrome occurring in physically active girls and women. Its interrelated components are disordered eating, amenorrhea, and osteoporosis. Pressure placed on young women to achieve or maintain unrealistically low body weight underlies development of the Triad. Adolescents and women training in sports in which low body weight is emphasized for athletic activity or appearance are at greatest risk. Girls and women with one component of the Triad should be screened for the others. Alone or in combination, Female Athlete Triad disorders can decrease physical performance and cause morbidity and mortality. More research is needed on its causes, prevalence, treatment, and consequences. All individuals working with physically active girls and women should be educated about the Female Athlete Triad and develop plans to prevent, recognize, treat, and reduce its risks.

The epidemiology and pathogenesis of osteoporosis

Osteoporosis is an increasing health care concern as populations age throughout the developed and developing world. The social and economic costs of osteoporosis are due to its clinical outcome of fracture which increases exponentially with age. This review will highlight some of the key epidemiological aspects of osteoporosis incorporating areas of more recent interest. These include the definition; the magnitude of the problem encompassing differing incidence and prevalence patterns of both low bone mass and fracture in different cultural groups; the social consequences of fracture, including economic costs, morbidity and mortality; the evaluation of fracture risk, including the role of bone density, bone quality and the risk of falling; as well as an overview of some of the factors involved in determining low bone mass. Bone mineral density (BMD) is the most easily measured and accurate predictor of fracture risk. For any individual, BMD is the combination of their peak bone density and subsequent bone loss, both of which are influenced by genetic, hormonal and environmental factors. An understanding of key issues relating to this important disease may lead to earlier detection of the individual at high risk for fracture and rational approach to prevention and management.

Nonassociation of estrogen receptor genotypes with bone mineral density and estrogen responsiveness to hormone replacement therapy in Korean postmenopausal women

Hormone replacement therapy (HRT) prevents bone loss in postmenopausal women, but some women are resistant to therapy. A recently reported case of severe estrogen resistance caused by a germline mutation at the estrogen receptor (ER) gene locus suggests the possibility that other variants of the ER gene could be responsible for resistance to HRT and could also be an answer to the heritable components of bone density. Three restriction fragment length polymorphisms (RFLPs) at the ER gene locus, represented as BstUI (or B variant), PvuII, and XbaI, and their relationship to bone mineral density (BMD) and estrogen responsiveness to HRT were examined in 248 healthy postmenopausal women, aged 41-68 yr (mean +/- SD, 52.0 +/- 4.6 yr) in Korea. The BstUI restriction site was not found in Korean women. The distribution of the PvuII and XbaI RFLPs was as follows: PP, 35 (14.1%); Pp, 136 (54.8%); pp, 77 (31.1%) and XX, 18 (7.3%); Xx, 72 (29.0%); and xx, 158 (63.7%), respectively (capital letters signify the absence of and lower case letters signify the presence of the restriction site of each RFLP). There was no significant relation between ER genotypes and z score values of lumbar spine BMD. Also, no significant genotypic differences were found in the change in lumbar spine BMD and those in biochemical markers before and after 1 yr of HRT. These data indicate no significant effects of ER genotypes on BMD and estrogen responsiveness after HRT.

Lack of relationship between vitamin D receptor genotype and forearm bone gain in healthy children, adolescents, and young adults

Recent studies have suggested that genetic effects on bone mineral density (BMD) are related to allelic variation in the vitamin D receptor (VDR) gene. We examined 1) allelic influences of the VDR gene on BMD of the forearm, spine, hip, and whole body; and 2) allelic influences of the VDR gene on forearm BMD gain. Two hundred and seventy-three healthy boys and girls, aged 8.2-16.5 yr, at baseline were eligible. Forearm BMD was assessed with single photon absorptiometry at baseline. BMD gain was calculated as the annual percent change in BMD measured by single photon absorptiometry from the baseline and after 3.8 +/- 0.1 (+/-SD) yr. Calcium intake and physical activity were assessed by a detailed questionnaire at baseline and after 1 yr. VDR alleles were determined by BsaMI endonuclease restriction fragment analysis after PCR amplification. No significant differences in forearm BMD gain or in BMD assessed at the forearm, spine, hip, and whole body were observed among the three VDR genotypes. These findings did not change after adjusting for environmental factors such as calcium intake and physical activity or age, weight, height, and changes in weight and height during the observation period. In conclusion, our data do not support the idea that VDR genotypes are related to BMD gain or to BMD at the forearm, hip, spine, and whole body in healthy boys and girls, aged 8-21 yr. VDR genotyping is probably of little use for the detection of individuals who would benefit from increased calcium and physical activity to increase their peak bone densities.

Relations between calcium intake, calcitriol, polymorphisms of the vitamin D receptor gene, and calcium absorption in premenopausal women

The relations between calcium absorption, dietary calcium intake, 1,25-dihydroxyvitamin D3 (calcitriol), and vitamin D receptor (VDR) gene polymorphisms were evaluated in 99 healthy women who were approaching menopause (mean age: 47 y, range: 43-53 y). Dietary calcium was assessed by food-frequency questionnaire and calcium absorption was measured by a single-isotope radiocalcium test. VDR alleles were classified according to the presence (b, t, a) or absence (B, T, A) of the BsmI, TaqI, and ApaI restriction enzyme cutting sites. Radiocalcium absorption was positively related to serum calcitriol (r = 0.23, P < 0.05) and inversely related to dietary calcium intake (r = -0.26, P < 0.01). There was, however, no significant relation (r = 0.10) between serum calcitriol concentrations and dietary calcium. Radiocalcium absorption was higher in the bbaaTT haplotype (P < 0.05) and the aa genotype (P < 0.05), polymorphisms said to be associated with a higher bone density. We conclude that serum calcitriol and dietary calcium are independent determinants of calcium absorption in premenopausal women and that VDR gene polymorphisms influence calcium absorption.

The influence of family history of hip fracture on the risk of vertebral deformity in men and women: the European Vertebral Osteoporosis Study

There are few data exploring clustering of osteoporotic fractures within families. The aim of this study was to determine the influence of maternal and paternal history of hip fracture on the risk of vertebral deformity. 12,816 men and women aged 50 to 75 years were recruited from population based sampling frames across Europe. Subjects were invited to attend by letter of invitation for an interviewer administered questionnaire and lateral spinal radiographs. Vertebral deformity was defined morphometrically using the McCloskey-Kanis method. 6.4% of men and 7.1% of women reported that their mother had suffered a hip fracture, while 1.7% of both men and women reported that their father had suffered a hip fracture. A maternal history of hip fracture was associated with a modest increased risk of vertebral deformity in men [odds ratio (OR) 1.3, 95% confidence interval (CI) 1.0-1.8], the risk being greater among those aged 65 years and over (OR = 1.5; 95% CI 1.0-2.4) and in those from low prevalence areas. There was no increased risk in women. Paternal history of hip fracture was not associated with vertebral deformity in either sex. In conclusion, maternal history of hip fracture appears to be a risk factor for vertebral deformity, particularly in men.

Influence of the vitamin D receptor gene alleles on bone mineral density in postmenopausal and osteoporotic women

It is well established that genetic factors contribute to bone turnover and bone density. Evidence exists suggesting that a major part of this genetic influence may be due to polymorphisms in the vitamin D receptor (VDR) gene. However, it is not clear whether the VDR genotype effect persists in elderly women. In the present study, the relationship between the BsmI, ApaI, and TaqI polymorphisms in the VDR gene, and the bone mineral density (BMD) at the lumbar spine, the femoral neck (FN), and the proximal radius was investigated in a large group of elderly women (75.5 +/- 5.0 years) of Caucasian origin and in 84 Type I osteoporotic women (66.6 +/- 8.4 years). We did not find a correlation between the VDR genotypes and BMD in elderly women. However, a significantly higher FN-BMD was observed in obese (body mass index [BMI] > 30 kg/m2) versus nonobese (BMI < 30 kg/m2) women (p < 0.01). This relationship was observed for all BsmI genotypes. Furthermore, the FN-BMD of nonobese women with bb BsmI genotype was 5% higher than that of women with the BB genotype (p = 0.04). We conclude that the VDR gene polymorphisms influence the FN-BMD in nonobese postmenopausal women. In a second part of the study, possible correlations between the VDR gene polymorphisms and osteoporosis Type I were analyzed. Our data could not reveal any association between these parameters.

Vitamin D receptor polymorphisms, bone mineral density, and bone metabolism in postmenopausal Mexican-American women

Common polymorphisms in the vitamin D receptor (VDR) gene have been shown to correlate with bone mineral density (BMD). However, attempts to replicate the original findings in other populations have yielded variable results. These disparities may reflect ethnic or environmental differences in the expression of the VDR effect upon BMD. We examined a relatively ethnically homogeneous group of 103 healthy postmenopausal Caucasian women of Mexican descent living in Northern California. We determined the VDR genotype and measured the BMD at the lumbar spine and femoral neck by dual-energy X-ray absorptiometry, as well as several biochemical indices of mineral metabolism. The prevalence of the BB genotype, associated in previous studies with the lowest BMD, was 8% and highly linked to the tt genotype. Absolute and age-adjusted BMD at both hip and spine showed a trend toward lower BMD in the BB, AA, and tt genotypes, but this trend did not achieve statistical significance. There were no consistent intergroup differences in change in BMD over 2 years of follow-up, nor in mean serum concentrations of 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, osteocalcin, or total urinary pyridinolines. Intact parathyroid hormone concentrations were significantly higher in subjects with the AA genotype, with a trend toward higher values in those with the BB and tt genotypes as well. Our data suggest that there may be a decrease in BMD associated with the B, A, and t alleles, but the intergroup difference in BMD is 0.2-0.5 standard deviations (SD) at the lumbar spine and 0.3 SD at the femoral neck, decreases that are smaller than previously reported. Given the relatively low prevalence of the BB/tt genotype in Mexican-American Caucasians, a larger sample would be required to detect a significant association between VDR alleles and differences in BMD of the magnitude suggested by our data. We conclude that a genotype effect of this magnitude, if present, would be clinically relevant, but the impact on BMD is too small to detect with statistical significance in a study of this size.

Bone mineral density and bone markers in relation to vitamin D receptor gene polymorphisms in Chinese men and women

Whether vitamin D receptor gene (VDRG) polymorphism can be used as a predictor for bone turnover rate or bone mass remains controversial. Its role within various ethnic populations are also unsettled. We examined VDRG polymorphism using restrictive enzymes Bsm-I, Apa-I, and Taq-I in 155 men aged 22-88 and 113 premenopausal women aged 40-53. The bone mineral density (BMD) of the vertebrae (L2-4), proximal femur, and total body bone mineral content (tb-BMC) (women only), as well as urinary N-terminal crosslinked fragment of type I collagen (NTX), serum osteocalcin, bone isozyme of alkaline phosphatase, and caboxyterminal propeptide of type I procollagen levels were measured. Chinese men and women exhibited a low prevalence for B (absence of Bsm-I restriction site) phenotypes than white and Japanese. Within the tested samples there were 0.4% BB homozygotes, 6.7% Bb heterozygotes, and 93% bb homozygotes. The distributions of Apa-I polymorphism (9.0% AA, 42.5% Aa, and 48.5% aa) also differed from those reported for the white populations. Most of the Chinese men and women were TT homozygous (96.6%). A comparison of actual values and values adjusted for age and weight of tb-BMC and BMD at the lumbar spine, Trochanter, Ward's triangle, and femoral neck showed no significant difference among three subgroups in each of the three sets of polymorphism. Furthermore, the actual values and adjusted values (adjusted for age) of the four bone markers, respectively, showed no significant differences. We conclude that given the very low prevalence of the suspected high risk genotypes (B, A, and t), and the lack of difference among the polymorphic subgroups, VDRG polymorphism may not be an important determinant of the bone turnover rate and bone mass of Chinese men and women.

Determinants of premenopausal bone mineral density: the interplay of genetic and lifestyle factors

Bone mineral density (BMD) is a reflection of both genetic and lifestyle factors. The interplay of genetic (vitamin D receptor [VDR] gene polymorphisms) and lifestyle factors on BMD at the lumbar spine and proximal femur was examined in 470 healthy premenopausal women, aged 44-50 years, using a Hologic QDR 2000 densitometer. The objective of this study was to examine the genetic and lifestyle determinants of premenopausal BMD. Each participant was genotyped for BsmI polymorphism at the VDR gene locus. The presence of a restriction site within VDR, specified as bb (189, 40.2%) (n, %) was associated with reduced spinal BMD, whereas absence of this site in BB (97, 20.6%) conferred greater spinal BMD, as did the genotype Bb (184, 39.1%). Associations between smoking, alcohol use, oral contraceptives, education level, multivitamins, number of children, degree of obesity, body weight, physical activity, dietary calcium intake, and VDR genotype to BMDs were examined. VDR genotype, body weight, degree of obesity, physical activity, and dietary calcium intake were all significant determinants of BMD. The association of VDR genotype with BMD at the femoral neck appeared to be modified by calcium intake (BB and Bb: 0.797 +/- 0.11 g/cm2 vs. 0.844 +/- 0.11 g/cm2, interaction term, p = 0.06) for low (< 1036 mg/day) and high (> or = 1036 mg/day; upper quartile) calcium intakes, respectively. A similar trend was demonstrated for physical activity. These findings suggest that prophylactic interventions aimed at achieving and maintaining optimal BMD, such as greater calcium intake or physical activity, may be important in maximizing one's genetic potential for BMD.

Vitamin D receptor gene polymorphisms are not related to bone turnover, rate of bone loss, and bone mass in postmenopausal women: the OFELY Study

Vitamin D receptor (VDR) gene polymorphisms have been reported to account for most of the well established genetic influence on bone mineral density (BMD). However, discordant studies have been published and it is still not clear whether VDR genotypes influence bone mass accretion and/or postmenopausal bone loss. In this study, we analyzed VDR gene polymorphisms, i.e., that of BsmI, ApaI, and TaqI restriction enzymes in 268 untreated postmenopausal women 1-26 years postmenopausal. There were 37 BBAA homozygote (absence of BsmI and ApaI restriction sites on both alleles), 55 bbaa homozygote (presence of restriction sites on both alleles), and 176 heterozygotes. At baseline, women between the three genotypes did not differ significantly in age, years since menopause, body mass index (BMI), nor dietary calcium intake. We found no relationship between VDR genotypes and bone turnover assessed by three serum markers of bone formation and three urinary bone resorption markers, nor with BMD measured at the spine, hip, forearm, and whole body by dual-energy X-ray absorptiometry (DXA). Rates of bone loss assessed by repeated DXA measurements over 2 years were highly significant (p = 0.02-0.0001) at all skeletal sites except for the lumbar spine but did not differ between genotypes at any sites either before or after adjustment for potential confounding factors such as years since menopause, BMI, calcium intake, serum 25 hydroxyvitamin D levels, and baseline BMD. When we restricted the analysis to early postmenopausal women, within 10 years of menopause (n = 128), lumbar spine bone loss became significant, but no significant difference between VDR genotypes in the rate of bone loss measured at any site was found. We conclude that VDR genotypes are not predictive of bone turnover, rate of postmenopausal bone loss, and bone mass in either early or late postmenopausal women. In a subgroup of women with a low calcium intake (below 600 mg/day), we also found no significant differences between genotypes in BMD and the rate of bone loss measured at any site, although the sample size (n = 64) may be too small to detect small differences. In conclusion, these data, along with the absence of relationships between VDR gene polymorphisms and peak bone mass that we recently reported, suggest that the determination of VDR genotypes is probably not a useful clinical test for the risk assessment of osteoporosis.