Genetics of body mass stability and risk for chronic disease: a 28-year longitudinal study

Determining the stability of genome-wide factors in BMI between ages 40 to 69 years

Genome-wide association studies (GWAS) have successfully identified common variants associated with BMI. However, the stability of aggregate genetic variation influencing BMI from midlife and beyond is unknown. By analysing 165,717 men and 193,073 women from the UKBiobank, we performed BMI GWAS on six independent five-year age intervals between 40 and 72 years. We then applied genomic structural equation modeling to test competing hypotheses regarding the stability of genetic effects for BMI. LDSR genetic correlations between BMI assessed between ages 40 to 73 were all very high and ranged 0.89 to 1.00. Genomic structural equation modeling revealed that molecular genetic variance in BMI at each age interval could not be explained by the accumulation of any age-specific genetic influences or autoregressive processes. Instead, a common set of stable genetic influences appears to underpin genome-wide variation in BMI from middle to early old age in men and women alike.

Obesity and eating behavior from the perspective of twin and genetic research

Obesity has dramatically increased during the last decades and is currently one of the most serious global health problems. We present a hypothesis that obesity is a neuro-behavioral disease having a strong genetic background mediated largely by eating behavior and is sensitive to the macro-environment; we study this hypothesis from the perspective of genetic research. Genetic family and genome-wide-association studies have shown well that body mass index (BMI, kg/m²) is a highly heritable and polygenic trait. New genetic variation of BMI emerges after early childhood. Candidate genes of BMI notably express in brain tissue, supporting that this new variation is related to behavior. Obesogenic environments at both childhood family and societal levels reinforce the genetic susceptibility to obesity. Genetic factors have a clear influence on macro-nutrient intake and appetite-related eating behavior traits. Results on the gene-by-diet interactions in obesity are mixed, but emerging evidence suggests that eating behavior traits partly mediate the effect of genes on BMI. However, more rigorous prospective study designs controlling for measurement bias are still needed.

The role of genetic and environmental influences on the association between childhood ADHD symptoms and BMI

BACKGROUND/OBJECTIVES

Although childhood attention deficit hyperactivity disorder (ADHD) has been previously associated with concurrent and later obesity in adulthood, the etiology of this association remains unclear. The objective of this study is to determine the shared genetic effects of ADHD symptoms and BMI in a large sample of sibling pairs, consider how these shared effects may vary over time, and examine potential sex differences.

SUBJECT/METHODS

Sibling pair data were obtained from the National Longitudinal Study of Adolescent to Adult Health (Add Health); childhood ADHD symptoms were reported retrospectively during young adulthood, while three prospective measurements of BMI were available from young adulthood to later adulthood. Cholesky decomposition models were fit to this data using Mx and maximum-likelihood estimation. The twin and sibling sample for these analyses included: 221 monozygotic (MZ) pairs (92 male-male, 139 female-female), 228 dizygotic (DZ) pairs (123 male-male, 105 female-female), 471 full-sibling (FS) pairs (289 male-male, 182 female-female), 106 male-female DZ twin pairs, and 234 male-female FS pairs.

RESULTS

The magnitude of the association between childhood ADHD symptoms and BMI changed over time and by sex. The etiological relationship between childhood ADHD symptoms and the three prospective measurements of BMI differed for males and females, such that unique or non-shared environmental influences contributed to the relationship within males and genetic factors contributed to the relationship within females. Specifically, among females, genetic influences on childhood ADHD symptoms were partially shared with those effecting BMI and increased from adolescence to later adulthood (genetic correlation = 0.20 (95% CI: 0.07-0.36) in adolescence and 0.24 (95% CI: 0.10, 0.41) in adulthood).

CONCLUSION

Genetic influences on ADHD symptoms in childhood are partially shared with those effecting obesity. However, future research is needed to determine why this association is limited to females.

Differential models of twin correlations in skew for body-mass index (BMI)

Background

Body Mass Index (BMI), like most human phenotypes, is substantially heritable. However, BMI is not normally distributed; the skew appears to be structural, and increases as a function of age. Moreover, twin correlations for BMI commonly violate the assumptions of the most common variety of the classical twin model, with the MZ twin correlation greater than twice the DZ correlation. This study aimed to decompose twin correlations for BMI using more general skew-t distributions.

Methods

Same sex MZ and DZ twin pairs (N = 7,086) from the community-based Washington State Twin Registry were included. We used latent profile analysis (LPA) to decompose twin correlations for BMI into multiple mixture distributions. LPA was performed using the default normal mixture distribution and the skew-t mixture distribution. Similar analyses were performed for height as a comparison. Our analyses are then replicated in an independent dataset.

Results

A two-class solution under the skew-t mixture distribution fits the BMI distribution for both genders. The first class consists of a relatively normally distributed, highly heritable BMI with a mean in the normal range. The second class is a positively skewed BMI in the overweight and obese range, with lower twin correlations. In contrast, height is normally distributed, highly heritable, and is well-fit by a single latent class. Results in the replication dataset were highly similar.

Conclusions

Our findings suggest that two distinct processes underlie the skew of the BMI distribution. The contrast between height and weight is in accord with subjective psychological experience: both are under obvious genetic influence, but BMI is also subject to behavioral control, whereas height is not.

Steeper change in body mass across four decades predicts poorer cardiometabolic outcomes at midlife

OBJECTIVE

This study examined patterns of change in adiposity across four decades starting in young adulthood as well as associations between change and midlife cardiometabolic outcomes.

METHODS

BMI was assessed at ages 20, 40, 56, and 62 years in 977 male veterans from the Vietnam Era Twin Study of Aging. Age 62 (range 56-66) cardiometabolic outcomes included hypertension, diabetes, dyslipidemia, inflammation, and ischemic heart disease. Analyses included latent growth modeling (LGM), latent class growth modeling (LCGM), and logistic regression models.

RESULTS

Linear BMI slope was associated with all outcomes. Accelerated (quadratic) BMI slope was significantly associated with greater risk for hypertension, diabetes, dyslipidemia, and inflammation; odds ratios ranged from 1.93 (diabetes) to 3.15 (dyslipidemia). Initial BMI did not predict later outcomes. Linear slope contributed significant unique variance for diabetes and dyslipidemia even controlling for age 62 BMI. LCGM revealed three trajectories. Men with the relatively stable, lower BMI trajectory had significantly better outcomes than those with trajectories with accelerated increases, especially those including obesity.

CONCLUSIONS

How individuals reach late-midlife BMI is important. Steepness of BMI change across 40 years from young adulthood to late midlife, in addition to late-midlife BMI itself, was robustly associated with greater risk for poor cardiometabolic outcomes.

Longitudinal Investigation into Genetics in the Conservation of Metabolic Phenotypes in Danish and Chinese Twins

Longitudinal twin studies on long term conservation of individual metabolic phenotypes can help to explore the genetic and environmental basis in maintaining metabolic homeostasis and metabolic health. We performed a longitudinal twin study on 12 metabolic phenotypes from Danish twins followed up for 12 years and Chinese twins traced for 7 years. The study covered a relatively large sample of 502 pairs of Danish adult twins with a mean age at intake of 38 years and a total of 181 Chinese adult twin pairs with a mean baseline age of 39.5 years. Bivariate twin models were fitted to the longitudinal measurements taken at two time points (at baseline and follow-up) to estimate the genetic and environmental contributions to phenotype variation and correlation at and between the two time points. High genetic components in the regulation of intra-individual phenotype correlation or stability over time were estimated in both Danish (h²>0.75 except fasting blood glucose) and Chinese (h²>0.72 except blood pressure) twins; moderate to high genetic contribution to phenotype variation at the two time points were also estimated except for the low genetic regulation on glucose in Danish and on blood pressure in Chinese twins. Meanwhile the bivariate twin models estimated shared environmental contributions to the variance and covariance in fasting blood glucose in Danish twins, and in systolic and diastolic blood pressure, low and high density lipoprotein cholesterol in Chinese twins. Overall, our longitudinal twin study on long-term stability of metabolic phenotypes in Danish and Chinese twins identified a common pattern of high genetic control over phenotype conservation, and at the same time revealed population-specific patterns of genetic and common environmental regulation on the variance as well as covariance of glucose and blood pressure.

Genetic and Environmental Regulation on Longitudinal Change of Metabolic Phenotypes in Danish and Chinese Adult Twins

OBJECTIVE

The rate of change in metabolic phenotypes can be highly indicative of metabolic disorders and disorder-related modifications. We analyzed data from longitudinal twin studies on multiple metabolic phenotypes in Danish and Chinese twins representing two populations of distinct ethnic, cultural, social-economic backgrounds and geographical environments.

MATERIALS AND METHODS

The study covered a relatively large sample of 502 pairs of Danish adult twins followed up for a long period of 12 years with a mean age at intake of 38 years (range: 18-65) and a total of 181 Chinese adult twin pairs traced for about 7 years with a mean baseline age of 39.5 years (range: 23-64). The classical twin models were fitted to the longitudinal change in each phenotype (Δphenotype) to estimate the genetic and environmental contributions to the variation in Δphenotype.

RESULTS

Moderate to high contributions by the unique environment were estimated for all phenotypes in both Danish (from 0.51 for low density lipoprotein cholesterol up to 0.72 for triglycerides) and Chinese (from 0.41 for triglycerides up to 0.73 for diastolic blood pressure) twins; low to moderate genetic components were estimated for long-term change in most of the phenotypes in Danish twins except for triglycerides and hip circumference. Compared with Danish twins, the Chinese twins tended to have higher genetic control over the longitudinal changes in lipids (except high density lipoprotein cholesterol) and glucose, higher unique environmental contribution to blood pressure but no genetic contribution to longitudinal change in body mass traits.

CONCLUSION

Our results emphasize the major contribution of unique environment to the observed intra-individual variation in all metabolic phenotypes in both samples, and meanwhile reveal differential patterns of genetic and common environmental regulation on changes over time in metabolic phenotypes across the two samples.

A new look at the genetic and environmental coherence of metabolic syndrome components

OBJECTIVE

Metabolic syndrome, a clustering of risk factors including insulin resistance, dyslipidemia, central obesity, and hypertension, increases risk for cardiovascular disease and cognitive decline. The etiology of the risk factors' cohesion remains unclear. How genetic and environmental influences explained co-occurrence of metabolic syndrome components was examined.

METHODS

Continuous measures of body mass index (BMI), waist circumference, blood pressure (BP), fasting insulin and glucose, high-density lipoprotein cholesterol (HDL), and triglycerides from 1,193 middle-aged twin men participating in the Vietnam Era Twin Study of Aging at average age 62 (range 56-67) were analyzed using multivariate biometrical modeling.

RESULTS

Four heritable factors were found: adiposity (BMI, waist circumference), insulin resistance (glucose, insulin), lipids (HDL, triglycerides), and BP (systolic, diastolic). Heritabilities were 0.42-0.68. In the best-fitting model, insulin resistance, lipids, and adiposity comprised a higher-order latent genetic factor. Adiposity and BP shared genetic influences independent of the latent genetic factor. All factors aggregated on a latent unique environmental factor.

CONCLUSIONS

Metabolic syndrome components form the equivalent of two genetic factors. BP was genetically unrelated to insulin resistance and lipids. Adiposity was the only characteristic genetically and environmentally related to all other factors. These results inform strategies for gene discovery and prediction of health outcomes.

Socioeconomic modifiers of genetic and environmental influences on body mass index in adult twins

OBJECTIVE

Individual measures of socioeconomic status (SES) suppress genetic variance in body mass index (BMI). Our objective was to examine the influence of both individual-level (i.e., educational attainment, household income) and macrolevel (i.e., neighborhood socioeconomic advantage) SES indicators on genetic contributions to BMI.

METHOD

The study used education level data from 4,162 monozygotic (MZ) and 1,900 dizygotic (DZ) same-sex twin pairs (64% female), income level data from 3,498 MZ and 1,534 DZ pairs (65% female), and neighborhood-level socioeconomic deprivation data from 2,327 MZ and 948 DZ pairs (65% female). Covariates included age (M = 40.4 ± 17.5 years), sex, and ethnicity. The cotwin control model was used to evaluate the mechanisms through which SES influences BMI (e.g., through genetic vs. environmental pathways), and a gene-by-environment interaction model was used to test whether residual variance in BMI, after controlling for the main effects of SES, was moderated by socioeconomic measures.

RESULTS

SES significantly predicted BMI. The association was noncausal, however, and instead was driven primarily through a common underlying genetic background that tended to grow less influential as SES increased. After controlling for the main effect of SES, both genetic and nonshared environmental variance decreased with increasing SES.

CONCLUSIONS

The impact of individual and macrolevel SES on BMI extends beyond its main effects. The influence of genes on BMI is moderated by individual and macrolevel measures of SES, such that when SES is higher, genetic factors become less influential.

Imputing observed blood pressure for antihypertensive treatment: impact on population and genetic analyses

BACKGROUND

Elevated blood pressure (BP), a heritable risk factor for many age-related disorders, is commonly investigated in population and genetic studies, but antihypertensive use can confound study results. Routine methods to adjust for antihypertensives may not sufficiently account for newer treatment protocols (i.e., combination or multiple drug therapy) found in contemporary cohorts.

METHODS

We refined an existing method to impute unmedicated BP in individuals on antihypertensives by incorporating new treatment trends. We assessed BP and antihypertensive use in male twins (n = 1,237) from the Vietnam Era Twin Study of Aging: 36% reported antihypertensive use; 52% of those treated were on multiple drugs.

RESULTS

Estimated heritability was 0.43 (95% confidence interval (CI) = 0.20-0.50) and 0.44 (95% CI = 0.22-0.61) for measured systolic BP (SBP) and diastolic BP (DBP), respectively. We imputed BP for antihypertensives by 3 approaches: (i) addition of a fixed value of 10/5mm Hg to measured SBP/DBP; (ii) incremented addition of mm Hg to BP based on number of medications; and (iii) a refined approach adding mm Hg based on antihypertensive drug class and ethnicity. The imputations did not significantly affect estimated heritability of BP. However, use of our most refined imputation method and other methods resulted in significantly increased phenotypic correlations between BP and body mass index, a trait known to be correlated with BP.

CONCLUSIONS

This study highlights the potential usefulness of applying a representative adjustment for medication use, such as by considering drug class, ethnicity, and the combination of drugs when assessing the relationship between BP and risk factors.

Gene-by-age effects on BMI from birth to adulthood: the Fels Longitudinal Study

OBJECTIVES

Genome wide association studies have shown 32 loci to influence BMI in European-American adults but replication in other studies is inconsistent and may be attributed to gene-by-age effects. The aims of this study were to determine if the influence of the summed risk score of these 32 loci (GRS) on BMI differed across age from birth to 40 years, and to determine if additive genetic effects other than those in the GRS differed by age.

METHODS

Serial measures of BMI were calculated at 0, 1, 3, 6, 9, 12, 18, and 28 months, and 4, 7, 11, 15, 19, 23, 30, and 40 years for 1,176 (605 females, 571 males) European-American participants in the Fels Longitudinal Study. SOLAR was used for genetic analyses.

RESULTS

GRS was significant (P < 0.05) at ages: 6, 9 months, 4-15 years, and 23-40 years. Remaining additive genetic effects independently influenced BMI (P < 5.3 × 10(-5) , 0.40 < h(2) < 0.76). Some genetic correlations between ages were not significant. Differential GRS effects did not retain significance after multiple comparisons adjustments.

CONCLUSIONS

While well-known BMI variants do not appear to have significant differential effects, other additive genes differ over the lifespan.

Gene-environment interactions related to body mass: School policies and social context as environmental moderators

This paper highlights the role of institutional resources and policies, whose origins lie in political processes, in shaping the genetic etiology of body mass among a national sample of adolescents. Using data from Waves I and II of the National Longitudinal Study of Adolescent Health, we decompose the variance of body mass into environmental and genetic components. We then examine the extent to which the genetic influences on body mass are different across the 134 schools in the study. Taking advantage of school differences in both health-related policies and social norms regarding body size, we examine how institutional resources and policies alter the relative impact of genetic influences on body mass. For the entire sample, we estimate a heritability of .82, with the remaining .18 due to unique environmental factors. However, we also show variation about this estimate and provide evidence suggesting that social norms and institutional policies often mask genetic vulnerabilities to increased weight. Empirically, we demonstrate that more-restrictive school policies and policies designed to curb weight gain are also associated with decreases the proportion of variance in body mass that is due to additive genetic influences.

Stability and change in health behaviours as predictors for disability pension: a prospective cohort study of Swedish twins

Background

Stability or changes of health behaviours have not been studied in association with incidence of disability pension (DP). The aims were to (1) investigate if stability or changes in health behaviours predict DP due to musculoskeletal diagnosis (MSD), (2) to evaluate if an association exists for DP in general, and (3) after taking familial confounding into account.

Methods

The study sample was 16,713 like-sexed twin individuals born in Sweden between 1935-1958 (6195 complete twin pairs) who had participated in two surveys 25 years apart, were alive, and not pensioned at the time of the latest survey. Cox proportional hazards analysis was used to assess the associations (hazard ratios (HR) with 95% confidence intervals (CI)) between stability and change in health behaviours (physical activity, tobacco and alcohol use, body mass index (BMI)), and number of pain locations collected at two time points 25 years apart and the incidence of DP until 2008.

Results

During the follow-up, 1843 (11%) individuals were granted DP with 747 of these due to MSD. A higher proportion of women were granted DP than men. Increase in BMI and stable use of tobacco products were predictors for DP due to MSD (HR 1.21-1.48) and DP in general (HR 1.10-1.41). The stability in the frequency of physical activity and increased frequency of physical activity were protective factors for DP due to MSD only when accounting for familial confounding. However, the number of pain locations (stability, increase, or decrease) was the strongest predictor for future DP due to MSD (HR 3.69, CI 2.99-4.56) and DP in general (HR 2.15, CI 1.92-2.42). In discordant pair analysis, the HRs for pain were lower, indicating potential familial confounding.

Conclusions

Health behaviours in adulthood, including an increase in pain locations were associated with the incidence of DP. The association between physical activity and DP was especially related to adulthood choices or habits, i.e., the individual decision about frequency of exercising. Thus, it is important to e.g. increase public awareness of the potential beneficial effects of exercise throughout life to avoid permanent exclusion from the labour market for medical reasons.

Effects of social contact and zygosity on 21-y weight change in male twins

BACKGROUND

Recent evidence indicates that social contact is related to similarities in weight gain over time. However, no studies have examined this effect in a twin design, in which genetic and other environmental effects can also be estimated.

OBJECTIVE

We determined whether the frequency of social contact is associated with similarity in weight change from young adulthood (mean age: 20 y) to middle age (mean age: 41 y) in twins and quantified the percentage of variance in weight change attributable to social contact, genetic factors, and other environmental influences.

DESIGN

Participants were 1966 monozygotic and 1529 dizygotic male twin pairs from the Vietnam-Era Twin Registry. Regression models tested whether frequency of social contact and zygosity predicted twin pair similarity in body mass index (BMI) change and weight change. Twin modeling was used to partition the percentage variance attributable to social contact, genetic, and other environmental effects.

RESULTS

Twins gained an average of 3.99 BMI units, or 13.23 kg (29.11 lb), over 21 y. In regression models, both zygosity (P < 0.001) and degree of social contact (P < 0.02) significantly predicted twin pair similarity in BMI change. In twin modeling, social contact between twins contributed 16% of the variance in BMI change (P < 0.001), whereas genetic factors contributed 42%, with no effect of additional shared environmental factors (1%). Similar results were obtained for weight change.

CONCLUSION

Frequency of social contact significantly predicted twin pair similarity in BMI and weight change over 21 y, independent of zygosity and other shared environmental influences.

Stable genes and changing environments: body mass index across adolescence and young adulthood

The transition between adolescence and young adulthood is a developmentally sensitive time where children are at an increased risk for becoming overweight and developing obesity. Twin studies have reported that body mass index [BMI] is highly heritable, however, it remains unclear whether the genetic influences are sex-limited and whether non-additive genetic influences contribute to body mass index [BMI] during these ages. In the current report, we examined self-reported data on BMI in same [n = 2,744] and opposite-sex [n = 1,178] siblings participating in the National Longitudinal Study on Adolescent Health [Add Health]. To investigate whether the same or different genes contributed to BMI for both sexes, we fit quantitative sex-limited genetic models to three waves of data collection. At each of the three Waves of assessment, models that included additive genetic, individual-specific environment, and no sex-limited genetic influences fit the data most parsimoniously. Heritable effects on BMI at each of the three Waves were large for both sexes and ranged between .75 and .86. While genetic contributions across the ages were highly correlated, longitudinal analyses indicated that the relevant individual-specific environmental influences on BMI in adolescence and young adulthood change sizably. These results underscore the importance of understanding early genetic influences on BMI and highlight the role environmental experiences have at later ages when new genetic influences appear to make a small contribution to individual variation in BMI.

Ethnicity, body mass, and genome-wide data

This article combines social and genetic epidemiology to examine the influence of self-reported ethnicity on body mass index (BMI) among a sample of adolescents and young adults. We use genetic information from more than 5,000 single nucleotide polymorphisms in combination with principal components analysis to characterize population ancestry of individuals in this study. We show that non-Hispanic white and Mexican-American respondents differ significantly with respect to BMI and differ on the first principal component from the genetic data. This first component is positively associated with BMI and accounts for roughly 3% of the genetic variance in our sample. However, after controlling for this genetic measure, the observed ethnic differences in BMI remain large and statistically significant. This study demonstrates a parsimonious method to adjust for genetic differences among individual respondents that may contribute to observed differences in outcomes. In this case, adjusting for genetic background has no bearing on the influence of self-identified ethnicity.

Genes determine stability and the environment determines change in cognitive ability during 35 years of adulthood

Previous research has demonstrated stability of cognitive ability and marked heritability during adulthood, but questions remain about the extent to which genetic factors account for this stability. We conducted a 35-year longitudinal assessment of general cognitive ability using the Armed Forces Qualification Test administered to 7,232 male twins in early adulthood and readministered to a subset of 1,237 twins during late middle age. The proportion of variance in cognitive functioning explained by genetic factors was .49 in young adulthood and .57 in late middle age. The correlation between the two administrations was .74 with a genetic correlation of 1.0, indicating that the same genetic influences operated at both times. Genetic factors were primarily responsible for stability, and nonshared environmental factors were primarily responsible for change. The genetic factors influencing cognition may change across other eras, but the same genetic influences are operating from early adulthood to late middle age.

Genetic variation in female BMI increases with number of children born but failure to replicate association between GNbeta3 variants and increased BMI in parous females

Objective:As post-pregnancy weight retention in women is a risk factor for obesity later in life, we assessed the changes in magnitude of genetic and environmental variation in BMI due to parity in an Australian female sample, comprising 11,915 female twins and their sisters.Results:Total variance of BMI increased with parity, primarily driven by an increase in nonadditive genetic variance. This finding was of particular interest given Gutersohn et al's (2000) report of recessive association between post-partum weight retention and the 825T allele of theGNβ3gene (rs5443) at 12p13.31. Hence, we attempted to replicate this association and test an additional three SNPs also located near or onGNβ3(rs10744716 (upstream), rs5442 (exon 10), rs5446 (exon 11)) in a sample of 3131 females and 1693 males from 2585 twin families. No association was found between these SNPs among females, even when allowing for a genotype by parity effect. However, a significant association was observed among males for rs10744716 (χ22= 10.22,p= 0.006; effect size = 0.47kg/m2), representing a novel association between a region upstream ofGNβ3and male BMI.

Genetic and environmental contributions to BMI in adolescent and young adult women

The objective of this study was to determine the genetic and environmental contributions to variation in BMI over time in European-American (EA) and African-American (AA) adolescent and young adult women. Self-reported BMI (kg/m(2)) data from 2,816 EA (1,306 twin pairs, 56.5% monozygotic (MZ)) and 404 AA (178 twin pairs, 42.7% MZ) women at baseline (T1; median age 15 years) and 3,225 EA (1,511 twin pairs, 55.3% MZ) and 539 AA (252 pairs, 43.3% MZ) women at follow-up (T2; median age 22 years) from a Midwestern US, population-based twin registry were used to construct biometrical genetic models. For EA women, the majority of the variance in BMI was attributable to additive genetic effects at both time points (82% for each), with the remaining variance attributable to nonshared environment. Genetic and nonshared environment correlations between adolescent and young adult BMI were 0.87 and 0.23, respectively. Among AA women, nonadditive genetic effects comprised 68% of the variance at T1 and 73% at T2, and were highly correlated (r(D) = 0.94). The proportions of variance attributable to nonshared environment at T1 (29%) and T2 (25%) were more modestly correlated (r(E) = 0.31). The remaining variance in AA women could be attributed to additive genetic effects. Additive vs. nonadditive genetic effects contribute differentially to BMI in AA vs. EA adolescent and young adult women. Additional research is needed to better characterize the environmental and genetic factors related to BMI in persons of different races to aid understanding of the complex determinants of body weight in individuals.

Genetics of tracking of body mass index from birth to late middle age: evidence from twin and family studies

The persistence of obesity from early childhood to late middle age is well known. We reviewed the results from existing genetic studies on tracking of BMI to discover how much genetic and environmental factors contribute to this tracking of obesity. In total, we found 5 genetic longitudinal studies on childhood obesity and 8 on obesity in adulthood. One was an adoption study, 3 were family studies, and 9 were twin studies. All were based on Caucasian populations, and one included genetic level information (the FTO gene). Strong genetic continuity in BMI was found from early childhood to onset of adulthood. Although new genetic factors started to affect BMI during the growth period, genetic correlations remained high. Evidence of the effect of common environment on the tracking of BMI during childhood was also found. The heritability estimates reported in twin studies ranged from 0.57 to 0.86 for the trend of BMI from early adulthood to late middle age. The three family studies gave lower estimates. Important unresolved questions are the genetics of BMI change in old age, the genetics of body composition change, the genetic architecture of tracking of obesity in ethnic groups other than Caucasians, and the interplay between genes and environment underlying the development and tracking of obesity.