Genetic aspects of osteoporosis

Dietary Calcium Intake and Osteoporosis Risk in Arab Adults

Osteoporosis is a major public health concern in Saudi Arabia's aging population. There is particularly limited information on how diet affects bone loss in this ethnic group. The purpose of this study was to examine the association between dietary calcium (Ca) intake and osteoporosis risk in Saudi adults. A total of 1950 patients (416 males and 1534 females) with known risk factors for osteoporosis participated in this cross-sectional study. A short questionnaire (CaQ) was used to assess dietary Ca intakes in patients attending tertiary hospitals in Riyadh City. The prevalence of osteoporosis was 21.3% and was more common in females (93.5%). Patients with osteoporosis were older (p < 0.001) and had lower BMI (p < 0.001). Results showed that the overall mean Ca intake was only 445.1 mg/day (recommended dietary intake of 1300 mg/day). Tea intake (OR = 0.8 95%CI: 0.7-1.0; p = 0.02) and consumption of fish and eggs (OR = 0.9 95%CI: 0.8-1.0; p = 0.01) were significantly associated with a lower risk of osteoporosis. Furthermore, consumption of biscuits, cake and bread slices were significantly associated with higher incidence of osteoporosis (OR = 1.3 95%CI: 1.0-1.5; p = 0.02). In conclusion, extremely low dietary Ca intake was observed among Saudi adults already at risk of osteoporosis. A balanced diet including high amount of Ca, vitamin D and omega-3 fatty acids accompanied by limiting consumption of foods high in saturated fats and glycemic index may be helpful in reducing osteoporosis risk in the Saudi adult population.

Controlling Nutritional Status score and postmenopausal osteoporosis

OBJECTIVE

This study investigated the association between CONUT score and postmenopausal osteoporosis.

METHODS

Postmenopausal women who were seen at an outpatient clinic in a tertiary hospital for routine gynecologic examination between January 2017 and June 2022 were included in the study. Based on their T-scores, a total of 423 women were divided into two groups. Group 1 included 216 women with osteoporosis (T-score < -2.5 SD), and group 2 included 207 women with normal bone mineral density (T-score > -1 SD). The formula for the CONUT score corresponds to collection of scores from albumin, total cholesterol, and total lymphocyte count. Higher scores indicate poorer nutritional control.

RESULTS

Mean age and mean age at menopause were similar in both groups. The duration of menopause, however, was higher in the women with osteoporosis (11.55 ± 6.82 vs 9.202 ± 6.14 y, P < 0.001). The 25-hydroxy vitamin D level was low in both groups. Body mass index of women with normal bone mineral density was higher than that of women with osteoporosis (31.54 ± 4.19 vs 28.52 ± 4.43 kg/m 2 , P < 0.001). The CONUT scores of the two groups were calculated and found to be higher in women with osteoporosis (3.180 ± 1.804 vs 0.391 ± 0.687, P < 0.001). According to the receiver operating characteristic curve analysis of the CONUT score for predicting osteoporosis, the area under the curve was calculated as 0.932, with a sensitivity of 86.6% and a specificity of 91.1% ( P < 0.001).

CONCLUSIONS

Diet plays an important role in the development of osteoporosis. In this study, it was shown that there is a relationship between CONUT score and osteoporosis.

Genetics and Epigenetics of Bone Remodeling and Metabolic Bone Diseases

Bone metabolism consists of a balance between bone formation and bone resorption, which is mediated by osteoblast and osteoclast activity, respectively. In order to ensure bone plasticity, the bone remodeling process needs to function properly. Mesenchymal stem cells differentiate into the osteoblast lineage by activating different signaling pathways, including transforming growth factor β (TGF-β)/bone morphogenic protein (BMP) and the Wingless/Int-1 (Wnt)/β-catenin pathways. Recent data indicate that bone remodeling processes are also epigenetically regulated by DNA methylation, histone post-translational modifications, and non-coding RNA expressions, such as micro-RNAs, long non-coding RNAs, and circular RNAs. Mutations and dysfunctions in pathways regulating the osteoblast differentiation might influence the bone remodeling process, ultimately leading to a large variety of metabolic bone diseases. In this review, we aim to summarize and describe the genetics and epigenetics of the bone remodeling process. Moreover, the current findings behind the genetics of metabolic bone diseases are also reported.

Peak Bone Mass and Quantitative Ultrasound Bone Properties in Young Adulthood: A Study in the PEAK-25 Cohort of Women

Peak bone mass is normally reached in the third decade of life. Previously, in the population-based PEAK-25 cohort (n = 1061, age 25.5 ± 0.2), we demonstrated that bone mineral density in the population-based PEAK-25 cohort is comparatively high; therefore, this study aimed to determine if the calcaneus microarchitecture mirrored this. In the process, we describe normative quantitative ultrasound (QUS) values for 25-yr-old women and the relationship between QUS values and extremes of body weight. QUS variables speed of sound (SOS), broadband ultrasound attenuation (BUA), and stiffness index were measured. Young adult values were based on the manufacturer-supplied QUS reference values. Analyses were performed in the cohort as a whole, and additionally, to understand the relationship between body weight and QUS values in young women, the variables were categorized into octiles for weight or body mass index (BMI) and the lowest and highest octiles were compared. In the cohort, SOS values, reflecting bone density, were higher (108 ± 18%), whereas BUA values, reflecting bone complexity, were lower (90 ± 14%) compared to the young adult reference population. SOS did not correlate with body weight or BMI. In the cohort, overall correlations between BUA weight, and BMI were small and positive (Pearson's r coefficients 0.261 and 0.197, respectively; p < 0.001), although in the low-weight group, r coefficients were higher (r = 0.313 and 0.268; p < 0.05). In contrast, in the high-weight group, correlation with BUA values tended to be small, negative, and nonsignificant. Correlation between QUS and dual-energy X-ray absorptiometry-measured bone mineral density was low to moderate and significant at all skeletal sites (r = 0.37-0.52). Whereas coefficients tended to be higher in the low-weight group, the reverse was apparent for the low-BMI group. In these 25-yr-old women, a comparatively high dual-energy X-ray absorptiometry-measured bone mass is offset by less complex bone structures assessed by QUS. This may have implications for later osteoporosis assessment and future fracture risk.

Effects of Dairy Products Consumption on Health: Benefits and Beliefs--A Commentary from the Belgian Bone Club and the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases

Dairy products provide a package of essential nutrients that is difficult to obtain in low-dairy or dairy-free diets, and for many people it is not possible to achieve recommended daily calcium intakes with a dairy-free diet. Despite the established benefits for bone health, some people avoid dairy in their diet due to beliefs that dairy may be detrimental to health, especially in those with weight management issues, lactose intolerance, osteoarthritis, rheumatoid arthritis, or trying to avoid cardiovascular disease. This review provides information for health professionals to enable them to help their patients make informed decisions about consuming dairy products as part of a balanced diet. There may be a weak association between dairy consumption and a possible small weight reduction, with decreases in fat mass and waist circumference and increases in lean body mass. Lactose intolerant individuals may not need to completely eliminate dairy products from their diet, as both yogurt and hard cheese are well tolerated. Among people with arthritis, there is no evidence for a benefit to avoid dairy consumption. Dairy products do not increase the risk of cardiovascular disease, particularly if low fat. Intake of up to three servings of dairy products per day appears to be safe and may confer a favourable benefit with regard to bone health.

Nutrition and bone health in women after the menopause

Osteoporosis affects one out of three postmenopausal women. Their remaining lifetime risk of fragility fractures exceeds that of breast cancer. The risk of osteoporosis and/or fragility fractures can be reduced through healthy lifestyle changes. These include adequate dietary intakes of calcium, vitamin D and protein, regular weight-bearing exercise, reduction in alcohol intake and smoking cessation. European guidance for the diagnosis and management of osteoporosis in postmenopausal women recommends a daily intake of at least 1000 mg/day for calcium, 800 IU/day for vitamin D and 1 g/kg body weight of protein for all women aged over 50 years. The development of programs that encourage lifestyle changes (in particular balanced nutrient intakes) are therefore essential for the reduction of osteoporosis risk.

Pubertal timing, bone acquisition, and risk of fracture throughout life

Pubertal maturation plays a fundamental role in bone acquisition. In retrospective epidemiological surveys in pre- and postmenopausal women, relatively later menarcheal age was associated with low bone mineral mass and increased risk of osteoporotic fracture. This association was usually ascribed to shorter time exposure to estrogen from the onset of pubertal maturation to peak bone mass attainment. Recent prospective studies in healthy children and adolescents do not corroborate the limited estrogen exposure hypothesis. In prepubertal girls who will experience later menarche, a reduced bone mineral density was observed before the onset of pubertal maturation, with no further accumulated deficit until peak bone mass attainment. In young adulthood, later menarche is associated with impaired microstructural bone components and reduced mechanical resistance. This intrinsic bone deficit can explain the fact that later menarche increases fracture risk during childhood and adolescence. In healthy individuals, both pubertal timing and bone development share several similar characteristics including wide physiological variability and strong effect of heritable factors but moderate influence of environmental determinants such as nutrition and physical activity. Several conditions modify pubertal timing and bone acquisition, a certain number of them acting in concert on both traits. Taken together, these facts should prompt the search for common genetic regulators of pubertal timing and bone acquisition. It should also open epigenetic investigation avenues to pinpoint which environmental exposure in fetal and infancy life, such as vitamin D, calcium, and/or protein supplies, influences both pubertal timing and bone acquisition.

Quantitative ultrasound at the phalanges in a cohort of monozygotic twins of different ages

PURPOSE

The aim of our study was to evaluate bone quality by quantitative ultrasound (QUS) at the phalanges in 129 monozygotic twin couples, outlining the differences between growing subjects and adults.

MATERIALS AND METHODS

A total of 129 healthy monozygotic twin couples (42 of children under 18 years of age and 87 of adults) were studied by phalangeal QUS, measuring amplitude-dependent speed of sound (AD-SoS) and bone transmission time (BTT). Anthropometric data were also recorded.

RESULTS

In children AD-SoS and BTT were positively correlated with age (r = 0.91, r = 0.91), height (r = 0.88, r = 0.90) and weight (r = 0.81, r = 0.87); in adults AD-SoS was negatively related to age (r = -0.36), AD-SoS and BTT were positively related to height (r = 0.37, r = 0.58). Absolute value differences between twins for AD-SoS and BTT were significantly higher in adult twins (25.9 ± 21.9 for AD-SoS and 0.08 ± 0.08 for BTT) than in children (14.5 ± 12.4 for AD-SoS and 0.05 ± 0.04 for BTT).

CONCLUSION

Differentiation in bone tissue quality in twins increases with age, probably reflecting lifestyle, personal habits, likely acting through epigenetic mechanisms.

Bone health in adolescent females with anorexia nervosa: what is a clinician to do?

The objective of this case report is to present a pharmacologic strategy for treatment of adolescents with anorexia nervosa (AN) and low bone mineral density (BMD). We present a 17.5-year-old girl with a 3-year history of AN and longstanding inability to optimize nutrition and gain weight, and a decrease over time in her already low BMD. A year after treatment with the 17-β estradiol patch (100 mcg twice weekly) with cyclic oral progesterone (2.5 mg medroxyprogesterone acetate daily for days 1-10 of every month), her spine and hip BMD Z-scores improved, and a further decrease was prevented. This novel treatment is a consideration for girls with AN at greatest risk for low BMD. Adolescents with AN are at risk for low BMD, and the most effective treatment is weight and menses restoration, which can be difficult to attain and to sustain. Recent studies have shown promising results with pharmacological therapy for low BMD in AN. This article discusses current concepts related to bone loss in AN, and new pharmacologic considerations for adolescents at greatest risk for low BMD.

Vitamin D receptor gene BsmI, FokI, ApaI, TaqI polymorphisms and bone mineral density in a group of Turkish type 1 diabetic patients

Previous studies have suggested an influence of vitamin D receptor alleles on bone metabolism and on susceptibility to type 1 diabetes mellitus in different ethnic populations. We aimed to investigate the distribution of vitamin D receptor (VDR) alleles in relation to biochemical bone turnover parameters and bone densitometry measurements in a group of Turkish type 1 diabetic patients. One hundred and seventeen patients (M/F 57/60, 27.6 ± 7.3 y duration of diabetes 8.1 ± 6.3 y) and 134 healthy controls (M/F 61/73, 26.2 ± 5.3 y) were included in the study. Bone mineral density (BMD) was evaluated by dual-energy X-ray absorptiometry (DEXA). The vitamin D receptor gene (VDR) polymorphisms FokI, Bsm1, Apa1, and Taq1 were examined using a PCR-based restriction analysis. Serum levels of calcium, phosphor osteocalcin, intact parathyroid hormone, and C telopeptide were measured. Vitamin D receptor Bsm1 Fok1, Apa1, and Taq1 genotype distributions were not different between patient with diabetes and control groups. BMD was 0.77 ± 0.2 g/cm(2) vs. 0.97 ± 0.2 g/cm(2) (P = 0.0001) for the femur, 1.0 ± 0.1 g/cm(2) vs. 1.13 ± 0.1 g/cm(2) (P = 0.001) for type 1 diabetic patients and controls. Bone turnover markers were significantly lower in type 1 diabetic group. BMD measurements and bone metabolic markers were not different between the genotypes in either the patient with diabetes or the controls. The VDR gene polymorphisms, Bsm1, Fok 1, Apa1, and Taq1 showed no influence on bone metabolism in our group of type 1 diabetic patients.

Pubertal timing and body mass index gain from birth to maturity in relation with femoral neck BMD and distal tibia microstructure in healthy female subjects

Childhood body mass index (BMI) gain is linked to hip fracture risk in elderly. In healthy girls, menarcheal age is inversely related to BMI gain during childhood and to femoral neck areal bone mass density (aBMD) and distal tibia structural components at maturity. This study underscores the importance of pubertal timing in age-related fragility fracture risk.

INTRODUCTION

Recent data point to a relationship between BMI change during childhood and hip fracture risk in later life. We hypothesized that BMI development is linked to variation in pubertal timing as assessed by menarcheal age (MENA) which in turn, is related to peak bone mass (PBM) and hip fracture risk in elderly.

METHODS

We studied in a 124 healthy female cohort the relationship between MENA and BMI from birth to maturity, and DXA-measured femoral neck (FN) aBMD at 20.4 year. At this age, we also measured bone strength related microstructure components of distal tibia by HR-pQCT.

RESULTS

At 20.4 ± 0.6 year, FN aBMD (mg/cm(2)), cortical thickness (μm), and trabecular density (mg HA/cm(3)) of distal tibia were inversely related to MENA (P = 0.023, 0.015, and 0.041, respectively) and positively to BMI changes from 1.0 to 12.4 years (P = 0.031, 0.089, 0.016, respectively). Significant inverse (P < 0.022 to <0.001) correlations (R = -0.21 to -0.42) were found between MENA and BMI from 7.9 to 20.4 years, but neither at birth nor at 1.0 year. Linear regression indicated that MENA Z-score was inversely related to BMI changes not only from 1.0 to 12.4 years (R = -0.35, P = 0.001), but also from 1.0 to 8.9 years, (R = -0.24, P = 0.017), i.e., before pubertal maturation.

CONCLUSION

BMI gain during childhood is associated with pubertal timing, which in turn, is correlated with several bone traits measured at PBM including FN aBMD, cortical thickness, and volumetric trabecular density of distal tibia. These data complement the reported relationship between childhood BMI gain and hip fracture risk in later life.

Familial resemblance of bone mineral density in children with inflammatory bowel disease

BACKGROUND AND AIM

Low bone mineral density (BMD) has recently been recognized as a potential health problem in children with inflammatory bowel disease (IBD). Our aim was to investigate the familial resemblance of BMD in pediatric patients with IBD.

PATIENTS AND METHODS

In this population-based study from western Sweden, we assessed 144 children with IBD, 83 with ulcerative colitis, 45 with Crohn disease, 16 with indeterminate colitis, and their parents (136 mothers and 130 fathers) with dual-energy X-ray absorptiometry (DEXA). After adjustment for sex, age, weight, height, and parental IBD, we correlated the BMD of the patients to the BMD of their mothers, fathers, and the midparent value ([mother's BMD + father's BMD]/2) at different skeletal sites and calculated the Pearson correlation coefficient (r) to evaluate the extent of familial resemblance.

RESULTS

The BMD of the children with IBD was clearly related to the BMD of their parents. The strongest correlation was found in the femoral neck with r = 0.55 (P < 0.001, 95% CI 0.41-0.66) between BMD of the children and the midparent value. The group of children with IBD had an odds ratio of 5.96 for decreased BMD (lumbar spine z score < -1 standard deviation) given that decreased BMD was diagnosed in both parents.

CONCLUSIONS

We conclude that BMD in children and adolescents with IBD is significantly related to that of their parents. In a clinical setting, it may be helpful to assess the parents of children with IBD with DEXA to interpret the children's DEXA measurements.

Vitamin D receptor genotype BB is associated with higher serum osteocalcin in first pregnancy

AIM

Serum osteocalcin was shown in a previous study on first trimester pregnant women to correlate with bone density and to distinguish between fast and slow bone losers. The objective of the present study is to examine whether serum osteocalcin is related to vitamin D receptor (VDR) BsmI polymorphism in pregnant women.

STUDY DESIGN

We determined osteocalcin serum levels and VDR BsmI genotype in 97 healthy first trimester pregnant women consecutively recruited during six months.

RESULTS

BB (21%), Bb (38%) and bb (41%) genotypes showed similar osteocalcin serum levels. However, in primigravidas (n=38) the BB genotype was significantly associated with higher mean osteocalcin level (9.67 ng/mL) than the Bb (8.07 ng/mL) and the bb genotype (8.14 ng/mL), respectively (P<0.05). The VDR genotype was the only independent parameter to correlate with serum osteocalcin (P<0.05).

CONCLUSION

Only primigravidas show in the first trimester a relation between the bone formation parameter serum osteocalcin and the VDR genotype BB which indicates a higher risk of fractures. For further clinical applications serum osteocalcin and VDR genotype should be tested on a cohort of primigravidas including measurements of bone density.

Deleterious effect of late menarche on distal tibia microstructure in healthy 20-year-old and premenopausal middle-aged women

Late menarche is a risk factor for fragility fractures. We hypothesized that pubertal timing-dependent alterations in bone structural components would persist from peak bone mass to menopause, independent of premenopausal bone loss. We studied the influence of menarcheal age (MENA) on femoral neck BMD (FN aBMD) by DXA and microstructure of distal tibia by HR-pQCT in healthy young adult (YAD; 20.4 +/- 0.6 [SD] yr, n = 124) and premenopausal middle-aged (PREMENO; 45.8 +/- 3.4 yr, n = 120) women. Median of MENA was 13.0 +/- 1.2 and 13.1 +/- 1.7 yr in YAD and PREMENO, respectively. In YAD and PREMENO (n = 244), FN aBMD (R = -0.29, p = 0.013), as well as total volumetric BMD (Dtot; R = -0.23, p = 0.006) and cortical thickness (Ct.Th; R = -0.18, p = 0.011) of distal tibia were inversely correlated to MENA. After segregation by the median of MENA in EARLY and LATE subgroups, the significant influences of both MENA (p = 0.004) and chronological age (p < 0.0001) were observed for FN aBMD and trabecular bone volume fraction of the distal tibia with similar differences in T-scores between LATE and EARLY subgroups in YAD (-0.36 and -0.31 T-scores) and PREMENO (-0.35 and -0.42 T-scores) women. Ct.Th was negatively influenced by MENA, whereas trabecular thickness (Tb.Th) was negatively influenced by chronological age. There was a striking inverse relationship between cross-sectional area and Ct.Th (R = -0.57, p < 0.001). In conclusion, the negative influence of late menarcheal age at weight-bearing sites as observed by the end of skeletal growth remains unattenuated a few years before menopause and is independent of premenopausal bone loss. Alterations in both bone mineral mass and microstructural components may explain the increased risk of fragility fractures associated with later menarcheal age.

Selective breeding as a tool to probe skeletal response to high voluntary locomotor activity in mice

We present a novel mouse-model for the study of skeletal structure and evolution, based on selective breeding for high levels of voluntary wheel running. Whereas traditional models (originally inbred strains, more recently knockouts and transgenics) rely on the study of mutant or laboratory-manipulated phenotypes, we have studied changes in skeletal morphometrics resulting from many generations of artificial selection for high activity in the form of wheel running, in which mice engage voluntarily. Mice from the four replicate High Runner (HR) lines run nearly three times as many revolutions during days 5 and 6 of a 6-day exposure to wheels (1.12 m circumference). We have found significant changes in skeletal dimensions of the hind limbs, including decreased directional asymmetry, larger femoral heads, and wider distal femora. The latter two have been hypothesized as evolutionary adaptations for long-distance locomotion in hominids. Exercise-training studies involving experimental groups with and without access to wheels have shown increased diameters of both femora and tibiafibulae, and suggest genetic effects on trainability (genotype-by-environment interactions). Reanalysis of previously published data on bone masses of hind limbs revealed novel patterns of change in bone mass associated with access to wheels for 2 months. Without access to wheels, HR mice have significantly heavier tibiafibulae and foot bones, whereas with chronic access to wheels, a significant increase in foot bone mass that was linearly related to increases in daily wheel running was observed. Mice exhibiting a recently discovered small-muscle phenotype ("mini-muscle," [MM] caused by a Mendelian recessive gene), in which the mass of the triceps surae muscle complex is ∼50% lower than in normal individuals, have significantly longer and thinner bones in the hind limb. We present new data for the ontogenetic development of muscle mass in Control, HR, and MM phenotypes in mice of 1-7 weeks postnatal age. Statistical comparisons reveal highly significant differences both in triceps surae mass and mass-corrected triceps surae mass between normal and MM mice at all but the postnatal age of 1 week. Based on previously observed differences in distributions of myosin isoforms in adult MM mice, we hypothesize that a reduction of myosin heavy-chain type-IIb isoforms with accounts for our observed ontogenetic changes in muscle mass.

Vitamin D receptor gene polymorphisms and epithelial ovarian cancer risk

Epidemiologic and laboratory studies support a role for the vitamin D endocrine system in ovarian carcinogenesis. The association of ovarian cancer risk with polymorphisms in the vitamin D receptor (VDR) gene, including rs10735810 (FokI), rs11568820 (Cdx-2), rs1544410 (BsmI), rs7975232 (ApaI), rs731236 (TaqI), and BsmI-ApaI-TaqI combined genotypes, was examined among 313 women with epithelial ovarian carcinoma and 574 controls. Odds ratios (OR) and 95% confidence intervals (95% CI) were estimated using unconditional logistic regression. The associations of VDR polymorphisms with risk were generally inconsistent across ethnic groups. Among Caucasian women (72 cases, 148 controls), heterozygous and homozygous ApaI A allele carriers were at increased ovarian carcinoma risk compared with homozygous carriers of the ApaI a allele (OR 2.8, 95% CI 1.2-7.0 and OR 3.4, 95% CI 1.3-9.1; P(trend) = 0.02). Caucasian heterozygous carriers of FokI f allele were also at increased risk of ovarian carcinoma compared with homozygous carriers of the common allele (OR 2.5, 95% CI 1.3-4.8; P(trend) = 0.04). Among Japanese women (94 cases, 173 controls), ovarian cancer risk was significantly decreased (OR 0.5, 95% CI 0.3-0.9) among Cdx-2 A allele heterozygotes compared with homozygote G allele carriers (P(trend) = 0.03). Compared with the bbaaTT BsmI-ApaI-TaqI genotype, bbaATT and BBAAtt genotypes were associated with increased ovarian cancer risk in Caucasian women (OR 4.2, 95% CI 1.3-13.1 and OR 5.2, 95% CI 1.6-17.5), but not in Japanese women (OR 1.1, 95% CI 0.6-1.9 and OR 2.3, 95% CI:0.4-12.3). This investigation provides some evidence that polymorphisms in the VDR gene might influence ovarian cancer susceptibility.

The relative importance of genetics and phenotypic plasticity in dictating bone morphology and mechanics in aged mice: evidence from an artificial selection experiment

Both genetic and environmental factors are known to influence the structure of bone, contributing to its mechanical behavior during, and adaptive response to, loading. We introduce a novel approach to simultaneously address the genetically mediated, exercise-related effects on bone morphometrics and strength, using mice that had been selectively bred for high levels of voluntary wheel running (16 generations). Female mice from high running and control lines were either allowed (n=12, 12, respectively) or denied (n=11, 12, respectively) access to wheels for 20 months. Femoral shaft, neck, and head were measured with calipers and via micro-computed tomography. Fracture characteristics of the femoral head were assessed in cantilever bending. After adjusting for variation in body mass by two-way analysis of covariance, distal width of the femur increased as a result of selective breeding, and mediolateral femoral diameter was reduced by wheel access. Cross-sectional area of the femoral mid-shaft showed a significant linetype x activity effect, increasing with wheel access in high-running lines but decreasing in control lines. Body mass was significantly positively correlated with many of the morphometric traits studied. Fracture load of the femoral neck was strongly positively predicted by morphometric traits of the femoral neck (r2>0.30), but no significant effects of selective breeding or wheel access were found. The significant correlations of body mass with femoral morphometric traits underscore the importance of controlling for body size when analyzing the response of bone size and shape to experimental treatments. After controlling for body mass, measures of the femoral neck remain significant predictors of femoral neck strength.

Genetic variation at the low-density lipoprotein receptor-related protein 5 (LRP5) locus modulates Wnt signaling and the relationship of physical activity with bone mineral density in men

Polymorphisms in the LRP5 gene have been associated with bone mineral density (BMD) in men and/or women. However, the functional basis for this association remains obscure. We hypothesized that LRP5 alleles could modulate Wnt signaling and the relationship between physical activity and BMD. This genetic association study was performed in the population-based Framingham Study Offspring Cohort, and included a subset of 1797 unrelated individuals who provided blood samples for DNA and who had BMD measurements of the hip and spine. Ten single-nucleotide polymorphisms (SNPs) spanning the LRP5 gene were genotyped and used for association and interaction analyses with BMD by regression methods. LRP5 haplotypes were transiently co-expressed with Wnt3a, MesD and Dkk1 in HEK293 cells and their activity evaluated by the TCF-Lef reporter assay. Six out of ten SNPs in LRP5 were associated with one or more of the femur or spine BMDs in men or women after adjustment for covariates, and these associations differed between genders. In men< or =age 60 years, 3 SNPs were significantly associated with BMD: rs2306862 on Exon 10 with femoral neck BMD (p=0.01) and Ward's BMD (p=0.01); rs4988321/p. V667M with Ward's BMD (p=0.02); and intronic rs901825 with trochanter BMD (p=0.03). In women, 3 SNPs in intron 2 were significantly associated with BMD: rs4988330 for trochanter (p=0.01) and spine BMD (p=0.003); rs312778 with femoral neck BMD (p=0.05); and rs4988331 with spine BMD (p=0.04). For each additional rare allele, BMD changed by 3-5% in males and 2-4% in females. Moreover, there was a significant interaction between physical activity and rs2306862 in exon 10 (p for interaction=0.02) and rs3736228/p. A1330V in exon 18 (p for interaction=0.05) on spine BMD in men. In both cases, the TT genotype was associated with lower BMD in men with higher physical activity scores, conversely with higher BMD in men with lower physical activity scores. In vitro, TCF-Lef activity in presence of Wnt3a was significantly reduced in cells expressing LRP5 haplotypes carrying the T allele of exon 10 and 18 compared to the wild-type allele, whereas co-expression of Dkk1 completely inhibited Wnt3a response through all LRP5 haplotypes. In summary, genetic variation in exons 10 and 18 of the LRP5 gene modulates Wnt signaling and the relationship between physical activity and BMD in men. These observations suggest that Wnt-LRP5 may play a role in the adaptation of bone to mechanical load in humans, and may explain some gender-related differences in bone mass.

Quantitative ultrasound of the hand phalanges in a cohort of monozygotic twins: influence of genetic and environmental factors

OBJECTIVE

Our objective was to evaluate the similarities and differences in bone mass and structure between pairs of monozygotic twins as measured by means of the quantitative ultrasound (QUS) technique.

DESIGN

A cohort of monozygotic twins was measured by QUS of the hand phalanges using the DBM sonic bone profiler (IGEA, Carpi, Italy). The parameters studied were amplitude-dependent speed of sound (AD-SoS), ultrasound bone profile index (UBPI), signal dynamics (SDy) and bone transmission time (BTT). Linear correlation coefficients, multivariate linear analysis and the ANOVA test were used to assess intrapair associations between variables and to determine which factors influence the intrapair differences in QUS variables.

PATIENTS

One hundred and six pairs of monozygotic twins were enrolled in the study, 68 females and 38 males in the age range 5 to 71 years.

RESULTS

Significant intrapair correlations were obtained in the whole population and separately for males and females, regarding height ( r =0.98-0.99, p <0.0001), weight ( r =0.95-0.96, p <0.0001), AD-SoS ( r =0.90-0.92, p <0.0001), BTT ( r =0.94-0.95, p <0.0001) and other QUS parameters ( r >0.74, p <0.0001). Multivariate analysis revealed that intrapair differences between AD-SoS, SDy, UBPI and BTT are significantly influenced by age in the whole population and in the female population. Furthermore, the ANOVA test showed, for the female group, a significant increase in the intrapair differences in SDy and UBPI above 40 years.

CONCLUSIONS

A relative contribution of genetic factors to skeletal status could be observed by phalangeal QUS measurement in monozygotic twins. A significant increase in the intrapair difference in QUS parameters with increasing age and onset of menopause also suggests the importance of environmental factors in the female twin population.

Genes and osteoporosis

Genes play an important role in the development of osteoporosis. Twin and family studies have consistently shown that peak bone mass, ultrasound properties of bone, skeletal geometry, bone turnover, and fracture are heritable. Yet, as we report in this paper, few candidate genes have been implicated without ambiguity. Osteoporosis is thought to be a polygenic disorder, determined by multiple genes and environmental risk factors, each with small to modest effect on bone mass and fracture. Here we argue that future success in finding genes is only possible with improved study design and the use of more rigorous analytic approaches that are now becoming available.

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.

Tail suspension induces bone loss in skeletally mature mice in the C57BL/6J strain but not in the C3H/HeJ strain

We assessed the effects of tail-suspension in two skeletal genetic backgrounds, the high C3H/HeJ (C3H) and low C57BL/6J (B6) bone masses inbred mice (male, 4-months old). Cancellous bone mass and structural parameters were evaluated in distal femoral metaphysis by three dimensional microcomputed tomography. Bone cellular activities were evaluated by histomorphometry and measurements of alkaline phosphatase activity (ALP) and osteocalcin in blood and deoxypyridinoline (D-pyr) in urine. In C3H mice, 2- and 3-week unloading experiments were performed. After an early and transient decrease in body weight, a 2-week suspension period resulted in stimulation of both bone formation rate by 45% and active osteoclastic surfaces by 19%. D-pyr did not change, but ALP and osteocalcin levels increased by 18% and 72%, respectively, in 2-week suspended mice, and osteocalcin remained elevated by 30% in the 3-week suspended mice. Such cellular modifications allowed the C3H mice to maintain their initial bone mass and trabecular structural parameters even after a 3-week suspension period. In B6 mice, 1- and 2-week unloading experiments were performed. Tail suspension resulted in decreased body weight during the first days followed by an incomplete recovery during the second week of unloading. The resorption activity was unaffected by any suspension time period, whereas a decrease of 42.5% in bone formation rate and of 21.5% in ALP were seen by the end of the first week of suspension, both values being restored after a 2-week suspension period. At this latter time, trabeculae were thinner, leading to a 24.5% cancellous bone loss. Trabecular number and connectivity, rod-plate index, and degree of anisotropy were not modified. We concluded that C3H mice constituted a unique model in which genetic background overwhelmed the usual effects of reduced biomechanical usage in bone, whereas B6 mice, compared with the standardized rat model, offered an alternative model of bone loss in a mature skeleton.

Genetic and environmental factors affect bone density variances of families of men and women with osteoporosis

Our aim was to assess the relative impacts of genetics and environment in the families of osteoporotic patients and identify the best subgroup of patients to investigate the genes associated with osteoporosis. We recruited 36 men and 47 women with osteoporosis (probands), median age of 52 and 68 yr, and all their siblings (90) and offspring (83). The families were classified as young or old on the basis of the median age of the probands. We measured the bone mineral density at the femoral neck (FN) and lumbar spine (LS) adjusted for age and weight and standardized (Z-score). Physical activity, nutritional calcium, and alcohol and tobacco consumption were investigated. We compared the mean Z-score using linear mixed model and assessed the familial resemblance using intraclass correlation. The mean Z-scores of the families of osteoporotic patients were significantly negative at FN and LS, with no intergeneration or intergender differences. At FN, but not at LS, the mean Z-score was independently lower in the families of male probands (mean +/- SD: -0.57 +/- 0.96, female: -0.18 +/- 0.85, P = 0.012) and in young families (-0.58 +/- 0.94, old families: -0.11 +/- 0.83, P = 0.006). This suggested that the lower Z-score in the families of men with osteoporosis was related to their younger age. There was significant phenotypic resemblance among members in the families. In the families of female probands, the correlation between the probands and her siblings was weak and disappeared after adjustment on environment, and a resemblance appeared within their children (FN: r = 0.61) suggesting that different environment had masked the resemblance in this subgroup. In the families of male probands, a strong resemblance persisted after adjusting for environment, (proband-offspring at FN: r = 0.46 and within offspring at FN: r = 0.66, at LS: r = 0.61). This showed that resemblance was independent of a common measurable environment in these families of men with osteoporosis. In conclusion, mainly young osteoporotic patients, most of whom were male in our study, are affected by the genetic component.

Niemann-Pick disease type B: an unusual clinical presentation with multiple vertebral fractures

We report here a unique case of a 55-year-old woman presenting with a clinical picture of Parkinson disease, severe back pain, splenomegaly, and pronounced dyspnea. Radiographic examination of the spine showed multiple vertebral fractures. Niemann-Pick disease type B was diagnosed by findings of lipid-loaded histiocytes and a strongly reduced sphingomyelinase enzyme activity. She was homozygous for the deletion of codon 608 (delR608), which encodes an arginine residue in the Acid Sphingomyelinase gene. To investigate the cause of the unusual vertebral fractures, we screened for polymorphisms previously described as possibly associated with increased risk for osteoporosis and fractures. Our patient was heterozygous for the polymorphisms of the vitamin D receptor gene, the estrogen receptor gene, and the collagen 1A1gene. Increased physical activity after Parkinson treatment, a genetic predisposition, together with worsening disease due to interfering medications could explain the dramatic presentation of this patient. She was treated with cholesterol lowering drugs such as statins to decrease sphingomyelin synthesis, avoidance of drugs that inhibit sphingomyelinase, and bisphosphonates. No new fractures have occurred, but the interstitial lung disease has progressed.

Fatores de risco da osteoporose: prevenção e detecção através do monitoramento clínico e genético

A osteoporose é uma doença sistêmica caracterizada pela baixa massa óssea e deterioração da micro arquitetura do tecido ósseo. Consequentemente existe um aumento na fragilidade do osso e suscetibilidade à fratura, que é considerada o efeito clínico mais importante deste processo. Muitos estudos que se utilizam de modelos em gêmeos ou pais e seus descendentes têm confirmado o papel da herança genética no pico de massa óssea, na verdade o maior fator de risco da fratura. Neste artigo de revisão, são enfocados os prováveis genes envolvidos no processo de osteoporose, ressaltando a importância das interações entre gene- gene e gene-ambiente. Concernente à influência isolada do ambiente, são abordados os hábitos relacionados ao estilo de vida, à nutrição e ao tabagismo envolvidos no aparecimento dessa doença. Durante os próximos anos, o conhecimento baseado na genética molecular elucidará o processo osteoporótico. Do mesmo modo, os estudos clínicos se expandirão, visando contribuir para a detecção precoce da doença, permitindo assim a aplicação de medidas preventivas e terapêuticas adequadas.

Role of genetics in osteoporosis

Osteoporosis is a disease characterized by fragile bones and high susceptibility to low-trauma fractures. It is a serious health problem, especially in elderly women. Bone mineral density (BMD) has been employed most commonly as the index for defining and studying osteoporosis. BMD has high genetic determination, with heritability ranging from 50 to 90%. Various gene-mapping approaches have been applied to identify specific genes underlying osteoporosis, largely using BMD as the study phenotype. We review here the genetic determination of osteoporosis as defined by BMD and discuss a fundamental issue we encounter in genetic research in osteoporosis: the choice of phenotype(s) to study. We briefly summarize and discuss advantages and disadvantages of various approaches used in genetic studies of osteoporosis. Finally, we review and discuss the current status for mapping and identification of genes for osteoporosis. We focus on linkage studies in humans and quantitative trait loci mapping in mice to supplement the already extensive reviews of association studies made by many investigators for candidate genes.

Bone mineral density and body composition in boys with distal forearm fractures: a dual-energy x-ray absorptiometry study

OBJECTIVE

To determine whether boys with distal forearm fractures differ from fracture-free control subjects in bone mineral density (BMD) or body composition.

STUDY DESIGN

A case-control study of 100 patients with fractures (aged 3 to 19 years) and l00 age-matched fracture-free control subjects was conducted. Weight, height, and body mass index were measured anthropometrically. BMD values and body composition were determined by dual-energy x-ray absorptiometry.

RESULTS

More patients than control subjects (36 vs l4) were overweight (body mass index >85th percentile for age, P <.001). Patients had lower areal (aBMD) and volumetric (BMAD) bone mineral density values and lower bone mineral content but more fat and less lean tissue than fracture-free control subjects. The ratios (95% CIs) for all case patients/control subjects in age and weight-adjusted data were ultradistal radius aBMD 0.94 (0.91-0.97); 33% radius aBMD 0.96 (0.93-0.98) and BMAD 0.95 (0.91-0.99); spinal L2-4 BMD 0.92 (0.89-0.95) and BMAD 0.92 (0.89-0.94); femoral neck aBMD 0.95 (0.92-0.98) and BMAD 0.95 (0.91-0.98); total body aBMD 0.97 (0.96-0.99), fat mass 1.14 (1.04-1.24), lean mass 0.96 (0.93-0.99), and total body bone mineral content 0.94 (0.91-0.97).

CONCLUSIONS

Our results support the view that low BMC, aBMD, and BMAD values and high adiposity are associated with increased risk of distal forearm fracture in boys. This is a concern, given the increasing levels of obesity in children today.

An assessment of genetic markers as predictors of bone turnover in healthy adults

In 1992 a significant relationship between bone turnover and the vitamin D receptor (VDR) genotype was reported in Australian subjects of UK-Irish decent. Since then, several groups have investigated the relationship between VDR and other bone-related genotypes, bone mass and bone turnover in several populations. However, the results of these studies are conflicting. Therefore, our aim was to determine bone-related genotypes in a population of healthy Irish adults and relate these genotypes to the rate of bone turnover. One hundred and eighteen healthy Irish adults (aged 19-67 yr) were recruited and fasting blood and first void urines were collected from each subject. Bone-related genotype frequencies in healthy Irish adults were similar to those reported in other Caucasian populations and were in Hardy-Weinberg equilibrium. Estrogen receptor (Pvu II or Xba I), apolipoprotein E and collagen IA1 genotypes were not related to bone turnover. The tt VDR genotype was associated with significantly higher serum osteocalcin (29% and 40%) compared with the Tt and TT genotypes, respectively. The ff VDR genotype was associated with significantly higher urinary pyridinoline (by approximately 44% and approximately 29%) and deoxypyridinoline (by approximately 76% and approximately 58%) levels and higher serum osteocalcin (by approximately 25% and approximately 53%) compared with the Ff or FF genotypes, respectively. These findings suggest that healthy Irish adults with either the tt or ff VDR genotype have higher rates of bone turnover than those with Tt or TT, or Ff or FF genotypes, respectively, and therefore may have a higher risk of low bone mineral density and osteoporosis in later life.

A functional polymorphic variant in the interleukin-6 gene promoter associated with low bone resorption in postmenopausal women

OBJECTIVE

To examine functional interleukin-6 (IL-6) -174 G-->C allelic variants in relation to bone turnover and bone mineral density (BMD) in postmenopausal women.

METHODS

Four hundred thirty-four healthy women living in the community (mean +/- SD age 71.7 +/- 5.7 years) were genotyped for the IL-6 -174 G-->C polymorphism. Serum levels of C-telopeptide of type I collagen (CTx), a marker of bone resorption, and osteocalcin (OC), a marker of bone formation, were determined. BMD at the hip and forearm was measured by dual-energy x-ray absorptiometry.

RESULTS

CTx levels differed significantly (P = 0.006) among IL-6 genotypes (mean +/- SEM 0.275 +/- 0.02 ng/ml, 0.325 +/- 0.01 ng/ml, and 0.356 +/- 0.02 ng/ml in women with the CC genotype [n = 68], the GC genotype [n = 204], and the GG genotype [n = 162], respectively). Compared with the GG group, age-adjusted odds ratios for high bone resorption were 0.65 (95% confidence interval [95% CI] 0.41-1.0, P = 0.06) and 0.37 (95% CI 0.18-0.73, P = 0.0047) in GC and CC subjects, respectively. In contrast, OC levels did not differ by genotype. BMD at the hip and forearm was 1.5-5% higher in CC subjects compared with GG subjects (P not significant). When the cohort was divided according to the median age (70.5 years), BMD was significantly decreased in older compared with younger postmenopausal women with the GG and GC genotypes (-9.6% on average; P < 0.01), but not in those with the CC genotype (-5.1% on average; P not significant).

CONCLUSION

Compared with the GC and GG IL-6 -174 G-->C genotypes, the CC genotype is associated with lower bone resorption and lesser decrease in bone mass in older postmenopausal women. These results suggest that IL-6 -174 G-->C alleles may be significant determinants of the risk for osteoporosis in elderly subjects.