Glucocorticoids contribute to the heritability of leptin in Scottish adult female twins

Variation in the heritability of body mass index based on diverse twin studies: a systematic review

OBJECTIVES

Over the past three decades, twin studies have shown variation in the heritability of obesity. This study examined the difference of body mass index (BMI) heritability (BMI-H) by population characteristics, such as sex, age, time period of observation and average BMI, as well as by broad social-environmental factors as indicated by country-level gross domestic product (GDP) per capita and GDP growth rate.

METHODS

Twin studies that reported BMI-H and were published in English from January 1990 to February 2011 after excluding those with disease, special occupations or combined heritability estimates for country/ethnic groups were searched in PubMed. 32 studies were identified from Finland (7), the United Kingdom (6), the United States (3), Denmark (3), China (3), Netherlands (2), South Korea (2), Sweden (2) and four from other countries. Meta-regression models with random effects were used to assess variation in BMI-H.

RESULTS

Heterogeneity of BMI-H is significantly attributable to variations in age (<20, 20-55 and ≥56 years), time period of observation (i.e. year of data collection), average BMI and GDP (≤$20,000, $20,001-26,000 and >$26,000). BMI-H was higher in adolescents (<20 years), in studies done in past years, and in populations with higher average BMIs or higher GDP per capita (≥$26,000) than their counterparts. Consistent lowering effects of high GDP growth rate (>median) on BMI-H were shown through stratified analyses by GDP. BMI-H was lower in countries of mid-level GDP, particularly those experiencing rapid economic growth.

CONCLUSIONS

BMI-H is sensitive to age, time period of observation, average BMI, GDP and rapid economic growth.

Genetic and environmental influences on adiponectin, leptin, and BMI among adolescents in Taiwan: a multivariate twin/sibling analysis

Circulating levels of leptin and adiponectin are closely associated with obesity. However, it is not known whether there are common shared genes or environment exerting influences on the levels of leptin, adiponectin, and BMI. We aimed to assess the relative contribution of genes and environment to adiponectin, leptin, and BMI individually as well as simultaneously to the three measures. Our subjects included a total of 228 twin/sibling pairs aged 12 to 18 (130 monozygotic twins, 68 dizygotic twins and 30 sibling pairs) were recruited from the middle schools. Multivariate analyses were applied to twin/sibling data using structural equation modeling. The results showed that intraclass correlations for adiponectin, leptin and BMI were higher in the MZ twins than those in the DZ/SP group. The relative contribution of genes to adiponectin (39%) was comparable to those of shared environment (40%). In contrast, leptin and BMI were influenced mostly by genes (74% and 89%, respectively). The multivariate genetic analyses showed that a latent factor underlying the three measures was identified, with BMI being equivalent to this latent factor. The BMI-dependent genetic factor explains only 15% and 34% of variation of adiponectin and leptin, respectively. These data indicate a differential contribution of genetic factors for the variation of adiponectin, leptin and BMI. More importantly, only a small portion of the genetic influences on adiponectin and leptin was attributed to BMI. Our findings provided more insight into the complex regulation of adiponectin and leptin in obesity.

Energy balance and food intake: the role of PPARgamma gene polymorphisms

Mechanisms regulating energy balance involve complex interactions between genetic, environmental and behavioural (learnt and intrinsic) factors. Genotype may drive the partitioning of energy metabolism and predispose to site-specific adiposity, culminating in a state of energy imbalance. One candidate gene with a direct link to adiposity is the peroxisome proliferator-activated receptor gamma (PPARG) gene. PPARG is a cell nuclear receptor expressed almost exclusively in adipose tissue that regulates adipocyte differentiation, lipid metabolism and insulin sensitivity. PPARgamma appears to be a key regulator of energy balance, with polymorphisms on the PPARG gene linked to obesity and effects on body composition. Our research has confirmed an association between the pro12ala allele and reduced incidence of obesity in pre-pubertal children and there are strong associations between genetic variation at the PPARG locus and percentage body fat. Moreover, our evidence suggests that PPARG C-681G and pro12ala polymorphisms display opposing effects in terms of growth phenotype, with pro12Ala associated with deficient energy utilisation, leading to reduced growth and the G-681 variant associated with accelerated growth compared with wildtypes. Common differences in this gene have also been associated with variations in body weight in response to dietary macronutrients. Preliminary evidence suggests that PPARG variants may even be involved in the control of short term energy compensation. Taken together these data suggest that the role of PPARG is varied and complex, influencing fat deposition and growth velocity early in life, with potential impact in the control of energy intake and appetite regulation, and could provide a key target for future research and anti-obesity agents.