Genetic Pleiotropy of Bone-Related Phenotypes: Insights from Osteoporosis.

PURPOSE OF REVIEW: We summarize recent evidence on the shared genetics within and outside the musculoskeletal system (mostly related to bone density and osteoporosis). RECENT FINDINGS: Osteoporosis is determined by an interplay between multiple genetic and environmental factors. Significant progress has been made regarding its genetic background revealing a number of robustly validated loci and respective pathways. However, pleiotropic factors affecting bone and other tissues are not well understood. The analytical methods proposed to test for potential associations between genetic variants and multiple phenotypes can be applied to bone-related data. A number of recent genetic studies have shown evidence of pleiotropy between bone density and other different phenotypes (traits, conditions, or diseases), within and outside the musculoskeletal system. Power benefits of combining correlated phenotypes, as well as unbiased discovery, make these studies promising. Studies in humans are supported by evidence from animal models. Drug development and repurposing should benefit from the pleiotropic approach. We believe that future studies should take into account shared genetics between the bone and related traits.

Intrauterine stress induces bone loss in adult offspring of C3H/HeJ mice having high bone mass phenotype but not C57BL/6J mice with low bone mass phenotype.

In this study we examined to what extent and how genetics may modify osteoporosis risk arising due to environmental stresses which act during the antenatal period of life and have the potential to induce bone loss in adulthood. C57Bl/6J (C57) and C3H/HeJ (C3H) mice were used as a model system. The mice were exposed to a single injection of 5-aza-2'-deoxycytidine (5-AZA) on day 10 of pregnancy and the structure and bone mineral density (BMD) of the femur and 3rd lumbar vertebra of 3- and 6-month-old male and female offspring were evaluated by micro-computed tomography (µCT). Besides, we also attempted to evaluate whether 5-AZA affects the expression of some osteogenic genes in the embryonic limb buds. The main observation of this study is that 5-AZA-induced loss of bone quality was registered in 6-mo-old C3H offspring but not in their C57 counterparts. We also observed that C57 and C3H embryos may differ in their response to 5-AZA-induced detrimental stimuli: whereas 5-AZA treated C3H embryos exhibited a decreased expression of Col1a1, C57 embryos exhibit a decreased expression of Sox9. Overall, our study, by thorough characterization of bone homeostasis in 3- and 6-month-old offspring of 5-AZA-exposed C57 and C3H mice, allows hypothesizing that the adaptive response to antenatal insults may be stronger in offspring inherently exhibiting a low bone mass phenotype than in offspring inherently exhibiting a high bone mass phenotype.

Gene transcripts associated with muscle strength: a CHARGE meta-analysis of 7,781 persons.

Lower muscle strength in midlife predicts disability and mortality in later life. Blood-borne factors, including growth differentiation factor 11 (GDF11), have been linked to muscle regeneration in animal models. We aimed to identify gene transcripts associated with muscle strength in adults. Meta-analysis of whole blood gene expression (overall 17,534 unique genes measured by microarray) and hand-grip strength in four independent cohorts (n = 7,781, ages: 20-104 yr, weighted mean = 56), adjusted for age, sex, height, weight, and leukocyte subtypes. Separate analyses were performed in subsets (older/younger than 60, men/women). Expression levels of 221 genes were associated with strength after adjustment for cofactors and for multiple statistical testing, including ALAS2 (rate-limiting enzyme in heme synthesis), PRF1 (perforin, a cytotoxic protein associated with inflammation), IGF1R, and IGF2BP2 (both insulin like growth factor related). We identified statistical enrichment for hemoglobin biosynthesis, innate immune activation, and the stress response. Ten genes were associated only in younger individuals, four in men only and one in women only. For example, PIK3R2 (a negative regulator of PI3K/AKT growth pathway) was negatively associated with muscle strength in younger (<60 yr) individuals but not older (≥ 60 yr). We also show that 115 genes (52%) have not previously been linked to muscle in NCBI PubMed abstracts. This first large-scale transcriptome study of muscle strength in human adults confirmed associations with known pathways and provides new evidence for over half of the genes identified. There may be age- and sex-specific gene expression signatures in blood for muscle strength.

The heritability of circulating testosterone, oestradiol, oestrone and sex hormone binding globulin concentrations in men: the Framingham Heart Study.

OBJECTIVE: Circulating testosterone, oestradiol and oestrone concentrations vary considerably between men. Although a substantial proportion of this variation may be attributed to morbidity and behavioural factors, these cannot account for its entirety, suggesting genetic inheritance as a potential additional determinant. The analysis described here was intended to estimate the heritability of male circulating total testosterone (TT), calculated free testosterone (cFT), oestrone (E1), oestradiol (E2) and sex hormone binding globulin (SHBG), along with the genetic correlation between these factors. DESIGN: Cross-sectional, observational analysis of data from male members of the Offspring and Generation 3 cohorts of the Framingham Heart Study. Data were collected in the years 1998-2005. PARTICIPANTS: A total of 3367 community-dwelling men contributed to the analysis, including 1066 father/son and 1284 brother pairs among other family relationships. MEASUREMENTS: Levels of serum sex steroids (TT, E1 and E2) were measured by liquid chromatography-tandem mass spectrometry, SHBG by immunofluorometric assay and cFT by mass action equation. Heritability was obtained using variance components analysis with adjustment for covariates including age, diabetes mellitus, body mass index and smoking status. RESULTS: Age-adjusted heritability estimates were 0·19, 0·40, 0·40, 0·30 and 0·41 for cFT, TT, E1, E2 and SHBG, respectively. Adjustment for covariates did not substantially attenuate these estimates; SHBG-adjusted TT results were similar to those obtained for cFT. Genetic correlation coefficients (ρG ) indicated substantial genetic association between TT and cFT (ρG = 0·68), between TT and SHBG (pG = 0·87), between E1 and E2 (ρG = 0·46) and between TT and E2 (ρG = 0·48). CONCLUSION: Circulating testosterone, oestradiol and oestrone concentrations exhibit substantial heritability in adult men. Significant genetic association between testosterone and oestrogen levels suggests shared genetic pathways.

Association of heat shock proteins with all-cause mortality.

Experimental mild heat shock is widely known as an intervention that results in extended longevity in various models along the evolutionary lineage. Heat shock proteins (HSPs) are highly upregulated immediately after a heat shock. The elevation in HSP levels was shown to inhibit stress-mediated cell death, and recent experiments indicate a highly versatile role for these proteins as inhibitors of programmed cell death. In this study, we examined common genetic variations in 31 genes encoding all members of the HSP70, small HSP, and heat shock factor (HSF) families for their association with all-cause mortality. Our discovery cohort was the Rotterdam study (RS1) containing 5,974 participants aged 55 years and older (3,174 deaths). We assessed 4,430 single nucleotide polymorphisms (SNPs) using the HumanHap550K Genotyping BeadChip from Illumina. After adjusting for multiple testing by permutation analysis, three SNPs showed evidence for association with all-cause mortality in RS1. These findings were followed in eight independent population-based cohorts, leading to a total of 25,007 participants (8,444 deaths). In the replication phase, only HSF2 (rs1416733) remained significantly associated with all-cause mortality. Rs1416733 is a known cis-eQTL for HSF2. Our findings suggest a role of HSF2 in all-cause mortality.

Circulating testosterone and SHBG concentrations are heritable in women: the Framingham Heart Study.

CONTEXT: Many factors influence the concentration of circulating testosterone and its primary binding protein, SHBG. However, little is known about the genetic contribution to their circulating concentrations in women, and their heritability in women is not well established. OBJECTIVE: Our objective was to estimate the heritability of circulating total testosterone (TT), free testosterone (FT), and SHBG in women in families from the Framingham Heart Study. METHODS: Women in the Framingham Heart Study who were not pregnant, had not undergone bilateral oophorectomy, and were not using exogenous hormones were eligible for this investigation. TT was measured using liquid chromatography tandem mass spectrometry and SHBG using an immunofluorometric assay (Delfia-Wallac), and FT was calculated. Heritability estimates were calculated using variance-components methods in Sequential Oligogenic Linkage Analysis Routines (SOLAR) and were adjusted for age, age(2), body mass index (BMI), BMI(2), diabetes, smoking, and menopausal status. Bivariate analyses were done to assess genetic correlation between TT, FT, and SHBG. RESULTS: A total of 2685 women were studied including 868 sister pairs and 688 mother-daughter pairs. Multivariable adjusted heritability estimates were 0.26 ± 0.05 for FT, 0.26 ± 0.05 for TT, and 0.56 ± 0.05 for SHBG (P < 1.0 × 10(-7) for all). TT was genetically correlated with SHBG [genetic correlation coefficient (ρG) = 0.31 ± 0.10] and FT (ρG = 0.54 ± 0.09), whereas SHBG was inversely correlated with FT (ρG = -0.60 ± 0.08). CONCLUSION: Circulating TT, FT, and SHBG concentrations in women are significantly heritable, underscoring the importance of further work to identify the specific genes that contribute significantly to variation in sex steroid concentrations in women. The strong shared genetic component among pairs of TT, FT, and SHBG concentrations suggests potential pleiotropic effects for some of the underlying genes.

Associations of APOE gene polymorphisms with bone mineral density and fracture risk: a meta-analysis.

UNLABELLED: To determine the association of the Apolipoprotein E (APOE) E4 gene polymorphism with bone mineral density (BMD) and fractures we conducted a meta-analysis of 17 reports. Despite lower trochanteric and lumbar BMD in APOE4 carriers, there is insufficient evidence to support a consistent association of APOE with bone health. INTRODUCTION: APOE has been studied for its potential role in osteoporosis risk. It is hypothesized that genetic variation at APOE locus, known as E2, E3, and E4, may modulate BMD through its effects on lipoproteins and vitamin K transport. The purpose of this study was to determine the association of the APOE-E4 gene polymorphism with bone-related phenotypes. METHODS: We conducted a meta-analysis that combined newly analyzed individual data from two community-based cohorts, the Framingham Offspring Study (N = 1,495) and the vitamin K clinical trial (N = 377), with 15 other eligible published reports. Bone phenotypes included BMD measurements of the hip (total hip and trochanteric and femoral neck sites) and lumbar spine (from the L2 to L4 vertebrae) and prevalence or incidence of vertebral, hip, and other fractures. RESULTS: In sex-pooled analyses, APOE4 carriers had a 0.018 g/cm(2) lower weighted mean trochanteric BMD than non carriers (p = 0.0002) with no evidence for between-study heterogeneity. A significant association was also detected with lumbar spine BMD (p = 0.006); however, inter-study heterogeneity was observed. Associations with lumbar spine and trochanteric BMD were observed predominantly in women and became less significant in meta-regression (p = 0.055 and 0.01, respectively). There were no consistent associations of APOE4 genotype with BMD at other skeletal sites or with fracture risk. CONCLUSIONS: Based on these findings, there is insufficient evidence to support a strong and consistent association of the APOE genotype with BMD and fracture incidence.

Contribution of gender-specific genetic factors to osteoporosis risk.

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

Polymorphisms in the endothelial nitric oxide synthase gene and bone density/ultrasound and geometry in humans.

Nitric oxide (NO), produced by endothelial cells, is a signaling molecule synthesized from l-arginine by nitric oxide synthases (NOS). NO is known to reduce the ratio of receptor activator of nuclear factor KappaB (RANKL)/osteoprotegerin (OPG), leading to decreased osteoclastogenesis and a reduction in bone resorption. Endothelial nitric oxide synthase (eNOS or NOS3) is the predominant constitutive isoform of nitric NOS within bone. Recently, a NOS3 polymorphism, Glu298Asp, previously implicated in osteoporosis, failed to demonstrate an association with bone mineral density (BMD), although there was some indication of an association with selected geometry indices. Since a single polymorphism does not capture all of the potential variants in a given gene, we investigated a broader coverage of the NOS3 gene with bone density/ultrasound and geometry indices in a sample of unrelated individuals from the Framingham Offspring Study. Our results indicated that the Glu298Asp polymorphism was not associated with BMD but suggested some haplotype-based associations in the linkage disequilibrium (LD) region that included the Glu298Asp polymorphism with several geometry indices. Although our findings exhibited several associations with selected bone density/ultrasound and geometry indices, the nominally significant associations are regarded as primarily hypothesis generating and suggest that replication in other samples is needed. Thus, NOS3 genetic variation does not appear to be a major contributor to adult bone density/ultrasound and geometry in our sample.

Bivariate linkage study of proximal hip geometry and body size indices: the Framingham study.

Femoral geometry and body size are both characterized by substantial heritability. The purpose of this study was to discern whether hip geometry and body size (height and body mass index, BMI) share quantitative trait loci (QTL). Dual-energy X-ray absorptiometric scans of the proximal femur from 1,473 members in 323 pedigrees (ages 31-96 years) from the Framingham Osteoporosis Study were studied. We measured femoral neck length, neck-shaft angle, subperiosteal width (outer diameter), cross-sectional bone area, and section modulus, at the narrowest section of the femoral neck (NN), intertrochanteric (IT), and femoral shaft (S) regions. In variance component analyses, genetic correlations (rho ( G )) between hip geometry traits and height ranged 0.30-0.59 and between hip geometry and BMI ranged 0.11-0.47. In a genomewide linkage scan with 636 markers, we obtained nominally suggestive linkages (bivariate LOD scores > or =1.9) for geometric traits and either height or BMI at several chromosomes (4, 6, 9, 15, and 21). Two loci, on chr. 2 (80 cM, BMI/shaft section modulus) and chr. X (height/shaft outer diameter), yielded bivariate LOD scores > or =3.0; although these loci were linked in univariate analyses with a geometric trait, neither was linked with either height or BMI. In conclusion, substantial genetic correlations were found between the femoral geometric traits, height and BMI. Linkage signals from bivariate linkage analyses of bone geometric indices and body size were similar to those obtained in univariate linkage analyses of femoral geometric traits, suggesting that most of the detected QTL primarily influence geometry of the hip.

Proximal hip geometry is linked to several chromosomal regions: genome-wide linkage results from the Framingham Osteoporosis Study.

INTRODUCTION: Femoral geometry contributes to bone strength and predicts hip fracture risk. The purpose of this study was to evaluate heritability (h(2)) of geometric indices of the proximal hip and to perform whole-genome linkage analyses of these traits, adjusted for body size. METHODS: DXA scans of the proximal femur from 1473 members of 323 pedigrees (age range 31-96 years) from the population-based Framingham Osteoporosis Study were obtained. Using the hip structural analysis program, we measured femoral neck length (FNL, cm) and neck-shaft angle (NSA); subperiosteal width (WID, cm), cross-sectional area (CSA, cm(2)); and section modulus (Z, cm(3)) at the narrowest section of the neck (NN), intertrochanteric (IT) and femoral shaft (S) regions. Linkage analyses were performed for the above indices with a set of 636 markers using variance components maximum likelihood method. RESULTS: Substantial genetic influences were found for all geometric phenotypes, with h(2) values between 0.28 (NSA) and 0.70 (IT_WID). Adjustment for height and BMI did not alter h(2) of NSA and FNL but decreased h(2) of the cross-sectional indices. We obtained substantial linkage (multipoint LOD >3.0) for S_Z at 2p21 and 21q11 and S_WID at Xq25-q26. Inclusion of height and BMI as covariates resulted in much lower LOD scores for S_Z, whereas linkage signals for S_Z at 4q25, S_CSA at 4q32 and S_CSA and S_Z at 15q21 increased after the adjustment. Linkage of FNL at 1q and 13q, NSA at 2q and NN_WID at 16q did not change after the adjustment. CONCLUSION: Suggestive linkages of bone geometric indices were found at 1q, 2p, 4q, 13q, 15q and Xq. The identification of significant linkage regions after adjustment for BMI and height may point to QTLs influencing femoral bone geometry independent of body size.

Abdominal aortic calcification and exostoses at the hand and lumbar spine: the Framingham Study.

Bony proliferation (exostoses) and vascular calcification are common in elderly men and women, but it is unclear whether they have a common etiology. Lateral lumbar and hand radiographs were obtained (1967-1970) in 777 men and 1,241 women (mean age 59, range 47-80 years) from the Framingham Heart Study. Each group of hand exostoses, specifically apiostoses (tufting), enthesophytes, and osteophytes, was graded on a scale of 0-3 (absent to severe) and summed across phalanges of digits 2-5. Anterior lumbar osteophytes were assessed in intervertebral spaces T12-L5 and abdominal aortic calcification (AAC) at lumbar segments L1-L4. Information on age, sex, body mass index, smoking, alcohol consumption, physical activity, systolic blood pressure, total cholesterol level, diabetes, and estrogen replacement therapy in women was obtained at the time of radiography and adjusted for in multivariate analyses. We used multivariable logistic regression models to assess the relationship between AAC (dependent variable) and exostoses for each sex. Multivariable adjusted logistic regression revealed a significant association between increased anterior lumbar osteophytes and prevalent AAC in men [odds ratio (OR) = 1.20, 95% confidence interval (CI) 1.1-1.3 per unit increase in osteophytes] and in women (OR = 1.25, 95% CI 1.1-1.4). There also was an inverse association between enthesophytes and AAC in women only (OR = 0.82, 95% CI 0.73-0.92). Apiostoses were weakly associated with AAC in men only. Hand osteophytes were not associated with AAC. In conclusion, in this cross-sectional study, anterior lumbar osteophytes and AAC occurred in the same individuals after adjustment for age and other covariates. In general, hand exostoses were not associated with aortic calcification.

Genome screen for a combined bone phenotype using principal component analysis: the Framingham study.

Genetic factors substantially contribute to variation in bone mass. There is a controversy as to whether shared genetic factors exist for bone mass at different sites. We hypothesize that using a composite phenotypic score of several correlated bone mass measures may provide complementary results for linkage studies. In the members of 323 pedigrees from the Framingham Osteoporosis Study, bone mineral density (BMD) was measured at the lumbar spine and three femoral sites (Lunar DPX-L), and quantitative ultrasound (QUS) measured at the calcaneus (Hologic Sahara). Data on age, sex, anthropometry, alcohol and caffeine intake, smoking status, physical activity, menopause, and estrogen use (in females) were also obtained. Principal component analyses of BMD and QUS phenotypes were performed in each sex and generation (parents and offspring). The principal component analyses yielded two components, whose loadings were extracted as principal component scores (PC1 and PC2) for each individual, with PC1 explaining up to 66% of the total variation of all bone mass measurements, and PC2 an additional 24%. Principal component analysis of the three femoral BMD measures resulted in one component (PC_hip) that explained 89-91% of the common variation of hip BMD measures. Quantitative genetic analysis (using the variance components method) revealed that both principal component scores were under significant genetic influences (covariate-adjusted heritabilities of PC1, PC2, and PC_hip were 0.66 +/- 0.07, 0.44 +/- 0.07, and 0.61 +/- 0.06, respectively). For PC1, loci of suggestive linkage were identified on chromosomes 1q21.3 and 8q24.3 with the maximum multipoint LOD scores 2.5 and 2.4, respectively. For PC2, multipoint LOD score was 2.1 on 1p36. Suggestive linkage of PC_hip was found on 8q24.3 and 16p13.2 (LODs>1.9). In conclusion, an approach to linkage analysis using the linear combination of several correlated bone phenotypes suggests that there are chromosomal loci regulating bone mass, with seemingly pleiotropic effects at different skeletal sites.

Age, gender, and body mass effects on quantitative trait loci for bone mineral density: the Framingham Study.

A genome-wide scan was performed in participants from the Framingham Osteoporosis Study (1557 members of 330 mostly Caucasian pedigrees), with 401 microsatellite markers spaced on average at 10 cM. Bone mineral density (BMD) was measured at the femoral neck, trochanter, Ward's area, and lumbar spine with DXA. Our recent study (J Bone Mines Res 17 (2002), 1718) reported a number of regions with suggestive linkage to possible quantitative trait loci (QTL). The current study estimates the heterogeneity of linkage in these regions in subsamples of our pedigrees, stratified on the known biological contributors to bone mass of sex, age, and body mass index (BMI). The pedigree sample was stratified into three sets of subgroups by sex [males (age range 35- 96 years), females (29-91 years)], by age [60 or younger (29-60 years) and older than 60 (61-96 years)], and by BMI [stratified into low or high BMI, by median cut-off 27.7 in males (BMI range 17-53) and 25.8 in females (14-54)]. Heritability estimates of BMD (adjusted for age, anthropometry, nutrition, physical activity, and, in females, estrogen use) in subsamples ranged from 0.47 to 0.69. Two-point and multipoint variance component linkage analyses of BMD (using SOLAR) in subsamples supported findings of previously reported suggestive linkage results in the total sample on 8q24.13 and 14q31 (LODs>2.0). However, heterogeneity of linkage was observed on 6p21.2 and 21qter, where findings in the total sample were not supported by subsamples. On the other hand, subsample-specific maxima were found, on 4q34.1 (males), 9q22-9q31 (younger), 16p13.2 (high BMI), and 17p13.3 (older), which were not reflected by the total sample results. In conclusion, heterogeneity of QTL effects was revealed in pedigree members stratified by sex, age, and BMI; in some instances new loci were identified in subgroups. These findings may suggest that effects of genes on the determination of BMD differ between men and women, younger and older, and lean and obese adults. Evaluation of family members stratified in homogeneous groups may be warranted in genetic studies of bone mass.

Mapping of quantitative ultrasound of the calcaneus bone to chromosome 1 by genome-wide linkage analysis.

Quantitative ultrasound (QUS) may predict the risk of fracture independent of bone density. The aim of this study was to identify, using quantitative trait linkage analysis, chromosomal regions that might contain genes influencing variation in calcaneal ultrasound measures in a set of families from the general population. A genome-wide autosomal scan was conducted in 324 Caucasian families (1270 measured individuals) from the Framingham Osteoporosis Study, using a set of 401 Marshfield microsatellite markers with a 10 cM average density map. QUS measurements included broadband ultrasound attenuation (BUA), speed of sound (SOS), and quantitative ultrasound index (QUI). These phenotypes were regressed on age, age(2), body mass index, height, alcohol and caffeine consumption, smoking status, physical activity, and estrogen use in females, in each sex and generation separately. Adjusted QUS phenotypes demonstrated a strong heritability ranging from 0.45 (SOS) to 0.52 (BUA). By two-point variance components genome screening, phenotype-specific regions of possible linkage were identified on chromosomal regions 1p36.3 and 5p15.2. The maximum LOD score attained was 2.74 for BUA with D1S468 (4 cM) and 2.69 for SOS with D5S817 (23 cM). QUI, a linear combination of the SOS and BUA, showed linkage with both markers (LOD = 2.1 with D1S468 and LOD = 2.2 with D5S817). Results of two-point analysis were confirmed by multipoint linkage analysis only for BUA, with LOD = 2.4 at D1S468, but not for SOS or QUI. The results for QUS, adjusted for femoral and lumbar spinal bone mineral density, in addition to the above covariates, were virtually the same. In conclusion, our results suggest that there may be genetic determinants for BUA on 1p36.3. These results should encourage further investigations of the genetic source of QUS variability and candidate polymorphisms in this region.

Genome screen for quantitative trait loci contributing to normal variation in bone mineral density: the Framingham Study.

A genome-wide scan was performed in a randomly ascertained set of 330 extended families from the population-based Framingham Study to identify chromosomal regions possibly linked to bone mineral density (BMD). A set of 401 microsatellite markers was typed at a 10-centimorgan (cM) average density throughout the genome. BMD was measured at the femoral neck, trochanter, Ward's area, and lumbar spine in 1557 participants of both Framingham cohorts. BMDs were adjusted for age, body mass index (BMI), height, alcohol, caffeine, calcium and vitamin D intakes, smoking, physical activity, and estrogen use in women within each sex and cohort. Strong heritabilities (values between 0.543 and 0.633) were found for the adjusted BMD at all sites. Two-point and multipoint quantitative linkage analyses were performed for each BMD site using the maximum likelihood variance components method. By two-point screening, loci of suggestive linkage were identified on chromosomes 6 and 21, with the maximum log10 of the odds ratio (LOD) scores of 2.34 for the trochanter at D21S1446 and 2.93 for the femoral neck at D6S2427. Lumbar spine BMD had maxima at D6S2427 (LOD = 1.88) and at D12S395 (LOD = 2.08). Multipoint linkage analysis revealed suggestive linkage of trochanteric BMD at a broad (approximately 20 cM) interval on chromosome 21q, with the peak linkage close to D21S1446 (LOD = 3.14). LOD scores were 2.13 at 8q24 with Ward's BMD and 1.92 at 14q21.3 with lumbar spine BMD. This largest genome screen to date for genes underlying normal variation in BMD, adjusted for a large number of covariates, will help to identify new positional candidate genes, otherwise unrecognized.

Insulin-like growth factor binding proteins 4 and 5 and bone mineral density in elderly men and women.

Insulin-like growth factor-1 (IGF-I) plays a central role in the maintenance of bone mass. To test whether two major IGF-I binding proteins, IGFBP-4 and IGFBP-5, are related to bone mineral density (BMD), we studied a sample of the Framingham Offspring Cohort participants (99 men and 101 women, ages 60-87). Serum levels of IGF-I, IGFBP-4, and IGFBP-5 were measured by previously validated radioimmunoassays (CVs approximately 10%). BMDs of the proximal femur and lumbar spine were measured using a Lunar DPX-L densitometer. In males, but not females, IGF-I and IGFBP-5 were inversely associated with age (r = 0.34 and r = -0.28, respectively; P <0.01), while IGFBP-4 levels were positively associated with age (P <0.01). Multivariate means for BMD (adjusted for age, body mass index, height, smoking, and in women, estrogen use) were computed across quartiles of IGFBP-4 and IGFBP-5 and IGFBP-4/IGFBP-5 ratio. In women, but not men, IGFBP-5 was positively associated with femoral neck BMD (P = 0.03), however, after statistical adjustment for IGF-I, this association was no longer significant. No other associations were observed for BMD at any other site. Further study is necessary for elucidation of the gender differences in the possible influence of IGF system components on bone mass.

Modelling of age-related bone loss using cross-sectional data.

BACKGROUND: Current applications of bone mineral density (BMD) data in age studies are not free of certain drawbacks. Since it is well established that age-related patterns of BMD changes involve three distinct periods (bone acquisition in youth, stabilization at maturity, and decrease with ageing), adjusting for age via an inappropriate mathematical function may lead to inconsistencies and wrong conclusions. HYPOTHESIS: The piecewise model, which encompasses the above three periods, will accurately describe the BMD dependence on age. OBJECTIVE: To examine age-related patterns of BMD changes using a number of possible mathematical functions and to find among them the best-fitting function. Next, to test whether the chosen function is universally applicable or if there are diverse population-specific functions. MATERIAL AND METHODS: Thirteen ethnic samples from various regions of Europe and Asia, assigned into five ethnic-geographic groups, were examined. The total sample included 2430 males and 2515 females. Compact BMD of hand phalanges was measured by photodensitometry from plain radiographs of each individual studied. Statistical software was developed for the purposes of the present study; this software gave a maximum likelihood of the parameter estimates for various statistical models (functions). RESULTS: In all samples of sufficient size and representative age range, a two-interval function was found as the best fitting and most parsimonious model to describe the BMD age-related changes. This two-interval function was characterized by age-related bone mass increase, positive slope beta(1s) in young age or a plateau (beta(1s) = 0, i.e. no age-related changes) until a sex-specific age threshold, T(0), after which annual bone loss ensued with a slope coefficient beta(2s). Threshold of BMD loss in women of different ethnic groups ranged between 37.85 and 47.77 years, and roughly coincided with perimenopausal age. In males, the age T(0) varied between 27.85 and 49.07 years. The ensuing cortical bone loss appeared to be linear in both sexes, averaging between 0.51% and 1.15% in men and between 0.74% and 1.77% per year of young age BMD value in females. CONCLUSIONS: The change of phalangeal BMD with age may be best described by a two-interval function, regardless of sex and ethnic background. However, specific parameter estimates depend both on gender and ethnic affiliation. This study has yielded a well-fitted model of BMD dependence on age suitable for further use in population studies.

Evidence on major gene control of cortical index in pedigree data from Middle Dalmatia, Croatia.

It was recently reported that the inheritance of the metacarpal cortical index (CI) in the Chuvashian population can be described in terms of a major gene (MG) model. By applying transmission probability tests, the hypothesis was accepted that not only baseline level of CI but also its sex-specific dependence on age were under control of the same putative large-effect gene. Using a pedigree sample from the population of the islands of Middle Dalmatia, Croatia (847 observed individuals in 278 pedigrees), data are presented to support the above findings. The following hypotheses were accepted: (i) inheritance of baseline CI in the Croatian population can be attributed to the effect of a MG responsible for about 42% of the variation; (ii) the same MG takes part in the control of the dependence of CI on age, particularly the age at onset of involutive bone changes (inflection point), and of the rate of decrease in CI with age (slope coefficient). Issues related to the assortative mating effect on CI and the determination of the most parsimonious model are discussed.

The effect of season, occupation and repeated winterings on anthropologic and physiological characteristics in Russian antarctic staff.

UNLABELLED: Thirty anthropometric and ten physiological parameters were examined over a 10-month-period in 1985-86, in 66 male polar explorers, aged 25-61 years, at an Antarctic station (Mirny observatory). For 30 of these persons this was their first wintering in Antarctic while the remaining 36 had wintered there at least once before. The mentioned measurements were taken on 3 different occasions in April, September and January corresponding in the Antarctic to the beginning of the polar night and interim season period and the beginning of the polar day. Subjects of the investigation belonged to 3 occupational groups: administrative personnel, scientific staff, and manual laborers. Extended statistical analysis of the data was carried out in an attempt to distinguish the dynamics of the studied parameters in relation to the season of wintering (Climate), the number of previous winterings (Frequency), the type of occupation (Work), and their interactions. Multifactorial statistical analyses were also performed, so as to adjust for age of subjects, which is a requisite for evaluating the factor of repeating winterings, obviously age-related. Changes in a number of characteristics were clearly recognized as connected with the factor of repeating winterings, to wit: 1) Anthropometric parameters such as or subcutaneous fat and relative muscle mass; 2) Parameters pertaining to speed of neuromuscular response such as wrist muscle effort, or time of simple motor response; and 3) Physiological parameters encompassing vascular--blood pressure and respiratory--spirometric measurements. CONCLUSION: Our findings suggest that frequency of repeated winterings is not a leading factor influencing physical status of examinees. Occupational status of examinees alone or in interaction with repeated winterings and seasonal climatic factors have more prominent impact on the well-being of polar explorers.