Growth and differentiation factor 15 is a biomarker for low back pain-associated disability.

The development of low back pain (LBP) is often associated with obesity and sarcopenia. However, the mechanisms of this association remain unclear. To clarify this, we measured circulating levels of a selected panel of soluble factors, presumably involved in obesity and sarcopenia pathogenesis, and correlated them with several LBP-related characteristics, taking into account body composition and other relevant covariates. In the cross-sectional study of 1078 individuals, we collected data on self-reported LBP, body composition (including fat and skeletal muscle mass) assessed by the bioimpedance method and anthropometrically, and measured plasma levels of several cytokines by ELISA. In the statistical analysis, we took into account familial composition of the sample and possible putative genetic effects. We report that LBP-affected individuals were significantly older, with increased obesity and decreased skeletal mass, respectively, compared with the non-affected group. In univariate analyses, plasma concentrations of Growth and differentiation factor 15 (GDF-15), leptin, chemerin and follistatin were found significantly elevated in the LBP-affected groups (with or without sciatic pain) and were highly significantly (p < 0.001) associated with other LBP-related phenotypes, specifically, disease duration, disability and physician consults. However, after adjustment for one another, age, sex, body composition and putative genetic factors, the only associations between GDF-15 and LBP disability and medical consulting phenotypes, remained significant. In conclusion, we report for the first time, a significant and independent association between plasma GDF-15 concentrations and LBP-associated disability. Longitudinal studies are needed to determine whether GDF-15 could be a novel therapeutic target for prevention and/or treatment of LBP.

Quantitative genetics of circulating Hyaluronic Acid (HA) and its correlation with hand osteoarthritis and obesity-related phenotypes in a community-based sample.

BACKGROUND: One of the potential molecular biomarkers of osteoarthritis (OA) is hyaluronic acid (HA). HA levels may be related to the severity and progression of OA. However, little is known about the contribution of major risk factors for osteoarthritis, e.g. obesity-related phenotypes and genetics to HA variation. AIM: To clarify the quantitative effect of these factors on HA. SUBJECTS AND METHODS: An ethnically homogeneous sample of 911 apparently healthy European-derived individuals, assessed for radiographic hand osteoarthritis (RHOA), HA, leptin, adiponectin, and several anthropometrical measures of obesity-related phenotypes was studied. Model-based quantitative genetic analysis was used to reveal genetic and shared environmental factors affecting the variation of the study's phenotypes. RESULTS: The HA levels significantly correlated with the age, RHOA, adiponectin, obesity-related phenotypes, and the waist-to-hip ratio. The putative genetic effects contributed significantly to the variation of HA (66.2 ± 9.3%) and they were also significant factors in the variations of all the other studied phenotypes, with the heritability estimate ranging between 0.122 ± 4.4% (WHR) and 45.7 ± 2.2% (joint space narrowing). CONCLUSIONS: This is the first study to report heritability estimates of HA variation and its correlation with obesity-related phenotypes, ADP and RHOA. However, the nature of genetic effects on HA and its correlation with other study phenotypes require further clarification.

Genetic determinants of circulating levels of tumor necrosis factor receptor II and their association with TNF-RII gene polymorphisms.

BACKGROUND: Tumor necrosis factor alpha (TNFalpha) is a cytokine involved in inflammatory, immune, and metabolic events. TNFalpha signals are mediated through activation of two receptors, one of which is tumor necrosis factor receptor TNF-RII. OBJECTIVE: To examine the effects of genetic and environmental factors on TNF-RII plasma concentration and its association with polymorphisms in the TNF-RII gene locus. METHODS: The levels of sTNF-RII were determined in 897 individuals. The association between sTNF-RII and polymorphisms in its structural gene locus was examined by pedigree-based association analyses (PDT) and transmission disequilibrium tests (TDTs). RESULTS: 49.57% of the adjusted sTNF-RII variability was attributable to genetic factors. sTNF-RII plasma levels were nominally associated with the genomic region spanning TNF-RII promoter and the first intron, represented by rs976881 (p=0.029). Although after correction for multiple testing this PDT signal formally did not reach statistical significance, it was reflected also in series of TDTs and further confirmed by association observed for haplotype of rs976881 with rs590368 (nominal p=0.006) and by ANOVA. CONCLUSIONS: sTNF-RII plasma concentration is determined by both genetic and environmental factors. Our results suggest association between sTNF-RII levels and polymorphisms in vicinity to TNF-RII promoter region. This finding requires further thorough validation in other populations.

Genetic regulation of the variation of circulating insulin-like growth factors and leptin in human pedigrees.

Recent literature has shown that circulating levels of insulin-like growth factor I (IGF-I) and/or IGF binding proteins (IGF-BPs) may be of importance in the risk assessment of several chronic diseases including cancer, cardiovascular disease, diabetes mellitus and so on. The present study examined the extent of genetic and environmental influences on the populational variation of circulating IGF-I and IGF-BP-1 in apparently healthy and ethnically homogeneous white families. The plasma levels of each of the studied biochemical indices were determined by enzyme-linked immunoassay in 563 individuals aged 18 to 80 years. Quantitative genetic analysis showed that the IGF-I variation was appreciably attributable to genetic effects (47.1% +/- 9.0%), whereas for IGF-BP-1, only 23.3% +/- 7.8% of the interindividual variation was explained by genetic determinants. Common familial environment factors contributed significantly only to IGF-BP-1 variation (23.3% +/- 7.8%). In addition, we examined the covariations between these molecules and between them and IGF-BP-3 and leptin that were previously studied in the same sample. The analysis revealed that the pleiotropic genetic effects were significant for 2 pairs of traits, namely for IGF-I and IGF-BP-3, and for IGF-BP-1 and leptin. The bivariate heritability estimates were 0.21 +/- 0.04 and 0.15 +/- 0.05. The common environmental factors were consistently a significant source of correlation between all pairs (barring IGF-I and leptin) of the studied molecules; they were the sole predictors of correlation between IGF-I and IGF-BP-1, and between IGF-BP-1 and IGF-BP-3. Our results affirm the existence of specific and common genetic pathways that in combination determine a substantial proportion of the circulating variation of these molecules.

Age and genetic determinants of variation of circulating levels of the receptor for advanced glycation end products (RAGE) in the general human population.

In stark contrast to many other blood biomarkers, including a variety of inflammatory cytokines, the main factors affecting sRAGE variation in the general human population are virtually unknown. We examined the contribution of age, body composition, and putative genetic sources to the interindividual variation of sRAGE. Its plasma levels were measured in 1557 apparently healthy individuals from 359 nuclear families. Statistical analysis revealed that all the aforementioned factors are statistically significantly associated with sRAGE levels. The levels of sRAGE consistently decreased with age (R=-0.264, p=<0.001) and with the indices of obesity, such as BMI. However, of special interest was the highly significant and previously not reported independent correlation with fat free mass (p<0.001). The putative genetic effects explained 0.291 ± 0.089 of sRAGE variation and were solely responsible for the phenotypic correlations with the obesity phenotypes (genetic correlations, -0.22 ± 0.09 and -0.33 ± 0.09). Taken together, these data suggest that although genetically determined to a substantial degree, the sRAGE levels also depend on age and obesity, which in turn, increase the risk for a variety of pathological conditions associated with sRAGE. Clearly, identifying the metabolic pathways and specific genetic factors is the next important stage in this research area.

Circulating levels of receptor activator of nuclear factor-kappaB ligand/osteoprotegerin/macrophage-colony stimulating factor in a presumably healthy human population.

OBJECTIVES: To determine the ranges of variation of circulating receptor activator of nuclear factor-kappaB ligand (RANKL)/osteoprotegerin (OPG)/macrophage-colony stimulating factor(M-CSF) and to ascertain their potential relationships with age, sex and menopausal status in women, and with sex hormones in a population-based healthy cohort. SUBJECTS AND METHODS: Blood samples were collected with EDTA after an overnight fast. The plasma levels of each of the above biochemical indices were measured by ELISA in a total of 566 apparently healthy individuals aged 18-75 years. RESULTS: The plasma concentrations of cytokine molecules in the entire sample ranged from 674 to 4929 pg/ml for OPG, from 105 to 4468 pg/ml for soluble RANKL (sRANKL), and from 187 to 7604 pg/ml for M-CSF. The OPG levels demonstrated a clear positive correlation with age in both sexes (r=0.42 and 0.43, P<0.001, for men and women respectively). Application of the two-interval mathematical model revealed that in females OPG levels were age-independent until age 42, but then showed clear and significant correlation with age (r=0.48, P<0.001). As a result, young females (before 42 years) had a substantially lower average OPG level, 1377.8+/-327.68 pg/ml, in comparison with older women, 1666.02+/-397.14 pg/ml. The M-CSF correlation with age was significantly greater in women (r=0.29, P<0.001) compared with men (r=0.17, P<0.01). Significant negative correlations between plasma levels of both OPG and M-CSF with estradiol concentrations were observed in women (r=-0.39, P<0.01; r=-0.25, P<0.001 respectively). sRANKL did not correlate with either age or sex hormones in either women or men. CONCLUSION: Age and sex affect differently the interindividual variation of OPG, RANKL and M-CSF. Our observations could form the basis for further research to establish provisional reference limits for OPG and RANKL, which are potential markers for benign and malignant processes in bone.

Assessment of age-related changes in heritability and IGF-1 gene effect on circulating IGF-1 levels.

It is well established that insulin-like growth factor 1 (IGF-1) circulating levels correlate with age and that heritability and influence of IGF-1 gene variation on IGF-1 levels also well-known. However, the influence of age on the genetic factors determining IGF-1 levels is not clear. In this study, we compared heritability estimates between younger (<52 years) and older (>52 years) twins and tested: (a) whether single nucleotide polymorphisms (SNPs) lying within 100 kbp of the IGF-1 gene are also associated with IGF-1 variation and (b) whether associated SNPs show interaction with age on IGF-1 levels. To achieve these aims, we measured plasma levels of IGF-1 and genotyped 18 SNPs with minor allele frequency >0.1 in a large sample, 4,471 UK female twins. Heritability explained 42 % of IGF-1 variation adjusted for age and in unadjusted sample was independent of age. Ten SNPs in four haploblocks showed significant association with IGF-1 levels, with p = 0.01-0.0005. The most distal SNP was located up to 90 kbp from the IGF-1 gene. When their age-dependent effects were examined, one SNP, rs855203, showed significant (p = 0.0009) age-dependent interaction effect on IGF-1 levels variation. This is the first study to test the age × genotype interaction in IGF-1 levels. The genomic region marked by rs855203 may consequently be of significance for further molecular and pharmacogenetic research, in particular in advanced age.

Elevated plasma fractalkine levels are associated with higher levels of IL-6, Apo-B, LDL-C and insulin, but not with body composition in a large female twin sample.

OBJECTIVE: Plasma fractalkine (FRACT) is involved in the development of numerous inflammatory conditions including atherosclerosis. It is associated with type 2 diabetes mellitus and adipose inflammation. However, whether FRACT is associated with major risk factors for cardiovascular disease, in particular obesity, metabolic syndrome and blood lipids, is virtually unknown. METHODS: The study included a large community-based sample of 3306 middle-aged women drawn from the general UK population. Blood samples were analyzed for circulating levels of FRACT, leptin, insulin, glucose, LDL-C, HDL-C, Apo-A, ApoB and IL-6. Obesity was assessed by fat body mass (FBM) using dual-energy x-ray absorptiometry and by body mass index (BMI). RESULTS: We found no association between FRACT and body composition, in particular adiposity. Obese and non obese subjects with metabolic syndrome tended to have higher levels of FRACT compared with non-obese subjects without metabolic syndrome but this did not reach statistical significance. Most importantly we report significant correlations between FRACT and circulating IL-6, Apo-B, LDL-C and insulin. The associations with IL-6 and Apo-B were particularly significant (P-value<0.001), and survived correction for multiple testing and adjustment for age and other covariates. CONCLUSION: Higher FRACT levels correlated with elevated levels of IL-6, Apo-B, LDL-C and insulin, all known risk factors for several clinical related diseases suggesting a potential role of FRACT in inflammation and tissue injury. Variations of FRACT levels are not influenced by body composition and are not correlated with leptin indicating that fat mass alone is not responsible for elevation of FRACT seen in obese individuals.

Contribution of putative genetic factors and candidate gene variants to inter-individual variation of circulating fractalkine (CX3CL1) levels in a large UK twins' sample.

OBJECTIVE: Soluble fractalkine (sFRACT) is involved in the pathogenesis of several clinical diseases. Our major objective was to determine to what extent its variation is governed by genetic factors and whether this genetic variation could be attributable to SNPs in five candidate genes: CX3CL1, CX3CR1, ADAM10, ADAM17 and AREG. METHODS: Plasma levels of sFRACT and 38 SNPs, with minor allele frequency >0.1 were examined in a large twin sample drawn from the general UK population. The discovery sample included 3306 middle-aged females: 1172 MZ twins and 2134 DZ twins. A replication sample of 1675 twins was used to validate the major association results obtained in genetic association analysis in the discovery sample. We implemented variance component analysis to estimate contribution of putative genetic, (including above SNPs) and environmental factors to sFRACT variation. RESULTS: sFRACT was found not to vary with either age or BMI. Putative genetic factors (heritability) explained 43.6±3% of the total variation of plasma sFRACT levels. However, we found no evidence of association between sFRACT and any of the examined SNPs, despite having >85% power to detect an association of just 1% of the variance explained. The results in the discovery and replication samples were in good agreement suggesting these findings are real. CONCLUSION: Our results suggest involvement of genetic factors to inter-individual variation of sFRACT levels in a general human population. However, further studies are required to determine genetic polymorphisms affecting sFRACT variation.

Significant association between body composition phenotypes and the osteocalcin genomic region in normative human population.

Osteocalcin, a major inorganic component of bone matrix and marker of bone formation, is also involved in regulation of glucose and fat mass metabolism. However, much uncertainty remains about whether the above effect on fat mass has a genetic component. Our main aim was to test whether a variation of body composition phenotypes is associated with BGLAP genomic region variants. To achieve this aim, we used an ethnically homogeneous discovery sample of 230 families consisting of 1112 apparently healthy individuals (561 males and 551 females) of European origin. We conducted association analysis between six SNPs and five obesity-related phenotypes: plasma levels of leptin, anthropometrical fat mass (FM), principal component scores of eight skinfold (SK_PC) and nine circumference (CR_PC) measurements, and body mass index (BMI). Two powerful and robust tools were applied: the pedigree disequilibrium test and variance component models, taking into account both familial and genetic effects. Significant association results were observed for all phenotypes. The most significant results were observed between the haplotype composed of three SNPs (rs2758605-rs1543294-rs2241106) and BMI (p=8.07(-7)), and CR_PC (p=5.29(-5)). The association with BMI was tested and confirmed in our replication study, including 2244 unrelated adult US Caucasians, who were previously assessed for whole genome SNP data. In addition, we obtained an evidence of potential non-additive interactions between the above three SNPs concerning their association with BMI. Bioinformatics sources suggest that the aforementioned interaction could originate from different genetic loci in this region; however, ascertaining the exact circumstances requires a detailed molecular-genetic study.

Genetic and environmental determinants of hepatocyte growth factor levels and their association with obesity and blood pressure.

BACKGROUND: Hepatocyte growth factor (HGF) is a member of the adipocytokine family; it is implicated in tissue repair, regeneration, and angiogenesis. Several studies have reported that the HGF plays important role in obesity and cardiovascular disease. AIM: This study examines whether HGF and its phenotypic correlations with obesity and blood pressure (BP), in healthy individuals, are due to shared genetic or common environmental factors. SUBJECTS AND METHODS: Body mass index (BMI), waist-to-hip ratio (WHR), BP, and HGF plasma concentrations were measured in a sample of 733 individuals belonging to 248 pedigrees. RESULTS: The most significant phenotypic correlations were found among HGF, WHR, and systolic BP (p < 0.001). Analysis of the familial aggregation revealed that parent-offspring and sibling correlations in HGF levels, adjusted for age, age(2), and sex, were statistically highly significant (p < 0.001). Variance decomposition analysis showed that when adjusted for potential covariates, 48.4% of the HGF variation was due to putative genetic factors. The genetic correlations between all pairs of studied traits (HGF, WHR, and SBP) were statistically significant (p < 0.02) and ranged between 0.23 +/- 0.07 and 0.40 +/- 0.07. However, correlation between WHR and BP becomes non-significant after adjustment for HGF. CONCLUSIONS: The results provide evidence that putative genetic factors involved in regulation of HGF variation contribute also significantly to variation of the obesity and BP. It is possible that the familial resemblance for WHR and the SBP correlation in the studied sample is affected substantially by genetic factors regulating circulating HGF levels.

Contribution of the putative genetic factors and ANKH gene polymorphisms to variation of circulating calciotropic molecules, PTH and BGP.

It is well known that regulation of calcium homeostasis in bone remodeling is one of the most crucial factors for maintaining healthy bones. Parathyroid hormone (PTH) is probably the most important hormone that participates in the bone remodeling process. Another important biochemical factor governing bone metabolism is osteocalcin (BGP). Although the physiological functions of both of these factors are well known, there is still very little known regarding their specific genetic determination and in particular, the specific genes that may regulate the circulating concentrations of these substances. In the present study, we examined whether nine single nucleotide polymorphisms (SNPs) in the human homologue of the mouse progressive ankylosis gene (ANKH)-one of the key genetic factors involved in bone mineralization-can be associated with PTH and BGP levels in apparently healthy human populations. The study sample comprised 244 nuclear families (840 individuals). After adjustment of BGP and PTH for the significant covariates (sex, age and BMI), the contribution of the putative genetic effects was statistically significant (P < 0.001) for both biochemical factors: 45.27 +/- 10.8% for PTH and 30.19 +/- 12.6% for BGP. Application of transmission disequilibrium tests (TDTs) revealed a significant association (P < 0.05) between PTH and two SNPs: rs39968 and rs875525. However, the association became particularly significant for four TDTs (P-values ranging from 0.0025 to 0.0008) when the association with the haplotypes generated from the above SNP was tested. This association remained significant even after correction for multiple testing with a false discovery rate of 0.05.

Genetic and environmental determinants of circulating levels of angiogenin in community-based sample.

BACKGROUND: Measurement of angiogenin in plasma provides important prognostic and diagnostic information in variety of malignancies and may even correlate with cancer's progression. Nevertheless, nowadays, specific physiological mechanisms of this protein action as well as major factors regulating its circulating levels normally and in pathology are still poorly understood. The main objectives of this study were to examine the contribution of a number of endogenous factors, such as sex, age, body size and genetic effects on the production of angiogenin in apparently healthy individuals, and to assess the correlations in circulating levels between angiogenin and other molecules involved in angiogenesis. METHODS: The plasma levels of angiogenin and each of the additional cytokines [interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF-alpha), transforming growth factor-beta (TGF-beta), macrophage-colony stimulating factor (M-CSF), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), soluble intercellular adhesion molecule-1 (sICAM)] were determined by enzyme-linked immunoassay in a large family based sample. RESULTS: Angiogenin levels were significantly higher in man than in women (360.64 +/- 104.04 ng/ml vs. 322.15 +/- 100.34 ng/ml, P < 0.01) and significantly correlated with age (P < 0.01) in both sexes. Genetic analysis showed that adjusted for potential covariates, 37.4 +/- 7.1% of angiogenin variation was attributable to putative genetic factors. The results of our study revealed that angiogenin concentrations were positively and significantly (P < 0.05) associated with sICAM, IL-6, TNF-alpha and M-CSF levels in the female cohort. CONCLUSIONS: Our data provide reliable evidence for the substantial role of genetic factors in the determination of the phenotypic variability of angiogenin plasma levels. These findings of our study, including circulating angiogenin reference limits in healthy population and its correlation with angiogenic cytokines, may be of importance in determination of early stages of pathological angiogenesis.

Genetic and environmental determinants of variation of soluble adhesion molecules.

In our research we examined the contribution of putative genetic sources on interindividual variation and cross-sectional correlations of several adhesion molecules, including intracellular (ICAM-1) and vascular cell adhesion molecules (VCAM-1) and E-selectin, in a population-based sample of ethnically homogeneous families of European origin. The plasma levels of these molecules were measured in 947 apparently healthy individuals from 217 nuclear families. Quantitative statistical-genetic analysis implementing the model fitting technique revealed significant parent/offspring and sibling correlations (p < 0.01) for all three molecules. The putative genetic effects explained 55.2 +/- 7.2% (VCAM-1), 63.3 +/- 7.5% (ICAM) and 63.8 +/- 8.1% (E-selectin) of the variation. Common family environmental factors also significantly influenced the variation of E-selectin (13%) and VCAM-1 (28.6%). The main results of our bivariate analysis showed that the observed phenotypic correlations between ICAM-1 and VCAM-1, and between ICAM-1 and E-selectin, were mostly attributable to shared environmental factors (r(E)= 0.896 and 0.737, respectively; p < 0.01). However, the correlation between VCAM-1 and E-selectin was likely caused by common genetic effects (r(G)= 0.334, p < 0.05). Our results show that familial clustering of adhesion molecules is likely due to strong genetic effects, supplemented with shared environmental factors.

Pedigree-based quantitative genetic analysis of interindividual variation in circulating levels of IGFBP-3.

Circulating levels of insulin-like growth factor binding protein-3 (IGFBP-3) vary greatly between normal individuals, but until now little attention has been given to the study of the genetic factors involved in IGFBP-3 variability in healthy populations. The present study investigated the extent and pattern of the possible genetic influences on plasma levels of IGFBP-3 in 91 nuclear and more complex families, totaling 396 individuals (201 males and 195 females) of Caucasian ethnic origin. The variance decomposition analysis, was performed using the FISHER statistical package. In the second stage of the analysis, we used complex segregation analysis as implemented in the statistical package MAN. Significant negative correlation was revealed between age and plasma levels of IGFBP-3 in both sexes ( r=-0.49; r=-0.23; P<0.001). Multivariate analysis identified age, body weight, and height as significant covariates in men, but for women only age had a considerable effect. It has been demonstrated that about 57.7% of IGBP-3 variation adjusted for significant confounding factors was attributable to genetic factors. The results of bivariate variance decomposition analysis showed no significant genetic and phenotypic correlation between the mineral density of hand bones and IGFBP-3. Segregation analysis revealed the existence of a potential major gene effect that was able to explain some 27.5% of IGFBP-3 variation. Multifactorial effects, likely, unknown minor genes, contributed an additional 30% to IGFBP-3 variation. The segregation analysis also provided evidence of significant genotype X sex interaction in the determination of plasma levels of IGFBP-3.

Genetic and environmental influences on IL-6 and TNF-alpha plasma levels in apparently healthy general population.

Dysregulation of cytokines synthesis is thought to play a role in the development of a number of age-related conditions, such as rheumatoid arthritis, osteoporosis, atherosclerosis, and others, but observational studies have led to contradictory results. We investigated potential familial influences on the plasma levels of IL-6 and TNF-alpha in 91 nuclear and more complex pedigrees of Caucasian ethnic origin (N=401 individuals). The maximum likelihood based variance decomposition analysis showed significant positive correlation between circulating IL-6 and age in both genders. The magnitude of these correlations in our sample ranged from 0.22 in females to 0.28 in males (P<0.001). Significant association between TNF-alpha and IL-6 (r=0.28, r=0.43; P<0.001; respectively for men and women) was also observed. Likelihood ratio test clearly revealed that additive genetic effect for TNF-alpha was highly significant (P<0.001), and accounted over 80% of its variation, adjusted for IL-6 levels and age. In contrast, heritability estimate for IL-6 adjusted for age and TNF-alpha, revealed small contribution of genetic factors (24.1 +/- 10.2%). The bivariate variance component analysis demonstrated that significant relationship between IL-6 and TNF-alpha was due to shared environment only (r(E)=0.760 +/- 0.140). As evinced from our complex segregation analysis the nature of the genetic determinant of each of these two cytokines is quite complex and it is probably oligogenic.

Genetic variation of circulating leptin is involved in genetic variation of hand bone size and geometry.

Leptin is secreted primarily by the adipocytes and plays an important role in the regulation of food intake and energy expenditure. In addition to its adipostatic function, it has been demonstrated that leptin directly enhances stromal cell differentiation to osteoblasts, and since such precursor cells are potential targets for leptin, the latter could possibly mediate the relationship between obesity and bone mass and size. To address this question, we studied phenotypic and genetic correlations between the circulating levels of leptin and hand bone size (BS) and geometry (BG) of the radiographic hand in a healthy and ethnically homogeneous sample of pedigrees. We also attempted to evaluate to what extent potential leptin/BS/BG correlations are modified by an individual's obesity traits, specifically his/her BMI. Our research has shown that leptin, BMI and the corresponding bone measures are clearly inherited traits (0.46+/-0.11, 0.35+/-0.16, 0.62+/-0.12 and 0.51+/-0.09, respectively). The bivariate variance component analysis revealed very strong and significant genetic and environmental correlations between circulating leptin and BMI ( r(G)=0.86+/-0.09, r(E)=0.75+/-0.05, P<0.001). Furthermore, genetic correlations between leptin and hand bone characteristics proved inverse and statistically significant ( r(G)=-0.35+/-0.01 and -0.45+/-0.10 for BS and BG, respectively), while corresponding environmental correlations were low ( r(E)=-0.14+/-0.15 and -0.07+/-0.14) and they could be constrained to zero without significant deterioration of the model fit to the data ( P>0.10). However, despite the extremely strong relationship between leptin and BMI, we failed to detect phenotypic or genetic correlations between BMI and our two hand bone measures. Thus our study provided evidence that plasma leptin levels may be statistically significant predictor of hand bone size and geometry, and may play a physiological role in maintaining bone mass as well as in regulation of hand bone proportions.