Leptin, insulin, and obesity-related phenotypes: genetic influences on levels and longitudinal changes

Associations Between Adiposity and Metabolic Syndrome Over Time: The Healthy Twin Study

BACKGROUND

We evaluated the association between changes in adiposity traits including anthropometric and fat mass indicators and changes in metabolic syndrome traits including metabolic syndrome clustering and individual components over time. We also assessed the shared genetic and environmental correlations between the two traits.

METHODS

Participants were 284 South Korean twin individuals and 279 nontwin family members had complete data for changes in adiposity traits and metabolic syndrome traits of the Healthy Twin study. Mixed linear model and bivariate variance-component analysis were applied.

RESULTS

Over a period of 3.1 ± 0.6 years of study, changes in adiposity traits [body mass index (BMI), waist circumference, total fat mass, and fat mass to lean mass ratio] had significant associations with changes in metabolic syndrome clustering [high blood pressure, high serum glucose, high triglycerides (TG), and low high-density lipoprotein cholesterol] after adjusting for intra-familial and sibling correlations, age, sex, baseline metabolic syndrome clustering, and socioeconomic factors and health behaviors at follow-up. Change in BMI associated significantly with changes in individual metabolic syndrome components compared to other adiposity traits. Change in metabolic syndrome component TG was a better predictor of changes in adiposity traits compared to changes in other metabolic components. These associations were explained by significant environmental correlations but not by genetic correlations.

CONCLUSIONS

Changes in anthropometric and fat mass indicators were positively associated with changes in metabolic syndrome clustering and those associations appeared to be regulated by environmental influences.

Exploring correlation between bone metabolism markers and densitometric traits in extended families from Spain

Osteoporosis is a common multifactorial disorder characterized by low bone mass and reduced bone strength that may cause fragility fractures. In recent years, there have been substantial advancements in the biochemical monitoring of bone metabolism through the measurement of bone turnover markers. Currently, good knowledge of the genetics of such markers has become an indispensable part of osteoporosis research. In this study, we used the Genetic Analysis of Osteoporosis Project to study the genetics of the plasma levels of 12 markers related to bone metabolism and osteoporosis. Plasma phenotypes were determined through biochemical assays and log-transformed values were used together with a set of covariates to model genetic and environmental contributions to phenotypic variation, thus estimating the heritability of each trait. In addition, we studied correlations between the 12 markers and a wide variety of previously described densitometric traits. All of the 12 bone metabolism markers showed significant heritability, ranging from 0.194 for osteocalcin to 0.516 for sclerostin after correcting for covariate effects. Strong genetic correlations were observed between osteocalcin and several bone mineral densitometric traits, a finding with potentially useful diagnostic applications. In addition, suggestive genetic correlations with densitometric traits were observed for leptin and sclerostin. Overall, the few strong and several suggestive genetic correlations point out the existence of a complex underlying genetic architecture for bone metabolism plasma phenotypes and provide a strong motivation for pursuing novel whole-genome gene-mapping strategies.

Changes in Weight and Cardiovascular Disease Risk Factors in Monozygotic Twins: The Healthy Twin Study

We aimed to assess the non-genetic contribution to the associations between the change in weight and changes in cardiovascular disease (CVD) risk factors. This analysis included 194 Korean monozygotic (MZ) twin pairs (116 men, 272 women; mean age, 38.5 ± 6.8 years) who were first examined for weight and CVD risk factors (blood pressure (BP), glucose, total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL), and low-density lipoprotein cholesterol (LDL)) between December 2005 and December 2008, and returned for a repeat examination after 2.7 ± 0.9 years. The within-pair correlations were 0.21 for the change in weight and 0.05-0.42 for the changes in CVD risk factors. Bivariate analyses showed significant environmental correlations shared between the change in weight and the changes in CVD risk factors (p < .05), except for glucose, while there were no significant genetic effects shared between the phenotypes. After adjusting for baseline values of weight, smoking, and alcohol consumption, diastolic blood pressure (DBP), TG, TC, and LDL significantly increased by 1.6 mmHg, 0.09 mmol/L, 0.10 mmol/L, and 0.09 mmol/L, respectively, per 1 kg increase in within-pair differences in weight change. In Korean MZ twins, similarity between twins for changes in weight and CVD risk factors were small to moderate, and non-genetic factors were responsible for the associations between the change in weight and changes in DBP, TG, TC, and LDL.

Variability in the heritability of body mass index: a systematic review and meta-regression

Evidence for a major role of genetic factors in the determination of body mass index (BMI) comes from studies of related individuals. Despite consistent evidence for a heritable component of BMI, estimates of BMI heritability vary widely between studies and the reasons for this remain unclear. While some variation is natural due to differences between populations and settings, study design factors may also explain some of the heterogeneity. We performed a systematic review that identified 88 independent estimates of BMI heritability from twin studies (total 140,525 twins) and 27 estimates from family studies (42,968 family members). BMI heritability estimates from twin studies ranged from 0.47 to 0.90 (5th/50th/95th centiles: 0.58/0.75/0.87) and were generally higher than those from family studies (range: 0.24-0.81; 5th/50th/95th centiles: 0.25/0.46/0.68). Meta-regression of the results from twin studies showed that BMI heritability estimates were 0.07 (P = 0.001) higher in children than in adults; estimates increased with mean age among childhood studies (+0.012/year, P = 0.002), but decreased with mean age in adult studies (-0.002/year, P = 0.002). Heritability estimates derived from AE twin models (which assume no contribution of shared environment) were 0.12 higher than those from ACE models (P < 0.001), whilst lower estimates were associated with self reported versus DNA-based determination of zygosity (-0.04, P = 0.02), and with self reported versus measured BMI (-0.05, P = 0.03). Although the observed differences in heritability according to aspects of study design are relatively small, together, the above factors explained 47% of the heterogeneity in estimates of BMI heritability from twin studies. In summary, while some variation in BMI heritability is expected due to population-level differences, study design factors explained nearly half the heterogeneity reported in twin studies. The genetic contribution to BMI appears to vary with age and may have a greater influence during childhood than adult life.

Parent-offspring transmission of adipocytokine levels and their associations with metabolic traits

Adipose tissue secreted cytokines (adipocytokines) have significant effects on the physiology and pathology of human metabolism relevant to diabetes and cardiovascular disease. We determined the relationship of the pattern of these circulating hormones with obesity-related phenotypes and whether such pattern is transmitted from parent to offspring. A combined total of 403 individuals from 156 consenting Saudi families divided into initial (119 families with 123 adults and 131 children) and replication (37 families with 58 adults and 91 children) cohorts were randomly selected from the RIYADH Cohort study. Anthropometrics were evaluated and metabolic measures such as fasting serum glucose, lipid profiles, insulin, leptin, adiponectin, resistin, tumor necrosis factor alpha (TNFα), activated plasminogen activator inhibitor 1 (aPAI1), high sensitivity C-reactive protein (hsCRP) and angiotensin II were also assessed. Parent-offspring regressions revealed that with the exception of hsCRP, all hormones measured showed evidence for significant inheritance. Principal component (PC) analysis of standardized hormone levels demonstrated surprising heritability of the three most common axes of variation. PC1, which explained 21% of the variation, was most strongly loaded on levels of leptin, TNFα, insulin, and aPAI1, and inversely with adiponectin. It was significantly associated with body mass index (BMI) and phenotypically stronger in children, and showed a heritability of ∼50%, after adjustment for age, gender and generational effects. We conclude that adipocytokines are highly heritable and their pattern of co-variation significantly influences BMI as early as the pre-teen years. Investigation at the genomic scale is required to determine the variants affecting the regulation of the hormones studied.

Morphological and biochemical features of obesity are associated with mineralization genes' polymorphisms

BACKGROUND

Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) was recently extensively studied as a candidate gene for obesity phenotypes. As the human homologue of the mouse progressive ankylosis (ANKH) and alkaline phosphatase (ALPL) are known functional partners of ENPP1 in bone mineralization, we hypothesized that these genes may also be jointly involved in determining obesity features.

AIM

To examine the effects of the three genes, possible gene-sex and gene-gene interactions on variability of four obesity phenotypes: the body mass index (BMI), the waist-hip ratio (WHR), the epidermal growth factor receptor (EGFR), and leptin.

SUBJECTS AND METHODS

In all, 962 healthy individuals from 230 families were genotyped for 45 single nucleotide polymorphisms (SNPs). The association analysis was performed using two family based association tests (family based association test and pedigree disequilibrium test). The combined P-values of the two tests were estimated by Monte-Carlo simulations. Relative magnitude of the genetic and familial effects, gene-sex and gene-gene interactions were assessed using variance component models.

RESULTS

Associations were observed between ENPP1 polymorphisms and BMI (P=0.0037) and leptin (P=0.0068). ALPL markers were associated with WHR (P=0.0026) and EGFR (P=0.0001). The ANKH gene was associated with all four studied obesity-related traits (P<0.0184), and its effects were modulated by sex. Gene-gene interactions were not detected.

CONCLUSION

The observed pattern of association signals indicates that ANKH may have a generalized effect on adipose tissue physiology, whereas ENPP1 and ALPL affect distinct obesity features. The joint analysis of related genes and integration of the results obtained by different methods used in this research should benefit other studies of similar design.

Metabolic syndrome-related composite factors over 5 years in the STANISLAS family study: genetic heritability and common environmental influences

BACKGROUND

We estimated genetic heritability and common environmental influences for various traits related to metabolic syndrome in young families from France.

METHODS

At entrance and after 5 years, nineteen traits related to metabolic syndrome were measured in a sample of families drawn from the STANISLAS study. In addition, 5 aggregates of these traits were identified using factor analysis.

RESULTS

At entrance, genetic heritability was high (20 to 44%) for plasma lipids and lipoproteins, uric acid, fasting glucose, and the related clusters "risk lipids" and "protective lipids". Intermediate or low genetic heritability (less than 20%) was shown for triglycerides, adiposity indices, blood pressure, hepatic enzyme activity, inflammatory makers and the related clusters: "liver enzymes", "adiposity/blood pressure" and "inflammation". Moreover, common environmental influences were significant for all the parameters. With regard to 5-year changes, polygenic variance was low and not statistically significant for any of the individual variables or clusters whereas shared environment influence was significant.

CONCLUSIONS

In these young families, genetic heritability of metabolic syndrome-related traits was generally lower than previously reported while the common environmental influences were greater. In addition, only shared environment contributed to short-term changes of these traits.