Gemini: A UK Twin Birth Cohort With a Focus on Early Childhood Weight Trajectories, Appetite and the Family Environment

Inherited behavioral susceptibility to adiposity in infancy: a multivariate genetic analysis of appetite and weight in the Gemini birth cohort

BACKGROUND

The behavioral susceptibility model proposes that inherited differences in traits such as appetite confer differential risk of weight gain and contribute to the heritability of weight. Evidence that the FTO gene may influence weight partly through its effects on appetite supports this model, but testing the behavioral pathways for multiple genes with very small effects is not feasible. Twin analyses make it possible to get a broad-based estimate of the extent of shared genetic influence between appetite and weight.

OBJECTIVE

The objective was to use multivariate twin analyses to test the hypothesis that associations between appetite and weight are underpinned by shared genetic effects.

DESIGN

Data were from Gemini, a population-based birth cohort of twins (n = 4804) born in 2007. Infant weights at 3 mo were taken from the records of health professionals. Appetite was assessed at 3 mo for the milk-feeding period by using the Baby Eating Behaviour Questionnaire (BEBQ), a parent-reported measure of appetite [enjoyment of food, food responsiveness, slowness in eating (SE), satiety responsiveness (SR), and appetite size (AS)]. Multivariate quantitative genetic modeling was used to test for shared genetic influences.

RESULTS

Significant correlations were found between all BEBQ traits and weight. Significant shared genetic influence was identified for weight with SE, SR, and AS; genetic correlations were between 0.22 and 0.37. Shared genetic effects explained 41-45% of these phenotypic associations.

CONCLUSION

Differences in weight in infancy may be due partly to genetically determined differences in appetitive traits that confer differential susceptibility to obesogenic environments.

Childbearing, stress and obesity disparities in women: a public health perspective

The perinatal period, from early in the first trimester to 1 year postpartum, provides opportunities for novel public health interventions to reduce obesity disparities. We present a unifying socio-biological framework to suggest opportunities for multidisciplinary research and public health approaches to elucidate and target the mechanisms for the development of maternal obesity and related disparities. The framework illustrates the interplay of the social, cultural and physical environment; stress appraisal and response; and coping behaviors on short-term outcomes (e.g. allostatic load and gestational weight gain), the intermediate outcomes of persistent insulin resistance and post-partum weight retention, and longer term outcomes of obesity and its disease consequences. Testing the proposed relationships may provide insights into how childbearing risk factors such as gestational weight gain, postpartum weight retention and parity contribute to obesity, which are needed to inform public health policies and clinical care guidelines aimed at reducing obesity and improving the health of women.

Prospective associations between appetitive traits and weight gain in infancy

BACKGROUND

Differences in appetitive traits such as food-cue or satiety responsiveness have been hypothesized to contribute to variability in weight gain. However, existing data were largely cross-sectional and could not exclude the possibility that differences in appetitive traits were consequences of differences in weight.

OBJECTIVE

We tested whether prospective associations between appetitive traits and subsequent weight were stronger than associations between weight and subsequent appetitive traits.

DESIGN

Data were from Gemini, which is a population-based cohort of 2402 families with twins. Parents completed a Baby Eating Behavior Questionnaire to assess 4 appetitive traits for each twin at ages 3 and 15 mo. We obtained infant weights at 3, 9, and 15 mo from records of health professionals. Weight SD scores were calculated by using UK 1990 reference data. A path analysis was used to examine prospective associations in each direction over sequential 6-mo intervals and over the same 12-mo period, with the significance of differences between the 2 paths established with bootstrapping.

RESULTS

Path analyses included 2213 infants. For each appetitive trait, the path to subsequent weight (standardized coefficients: 0.17-0.33) was significantly larger than the path from weight to subsequent appetite (coefficients: 0.07-0.13). Results were confirmed when both associations were analyzed by using changes from 3 to 15 mo.

CONCLUSION

Longitudinal analyses showed that associations between appetitive traits and subsequent weight were stronger than between weight and subsequent appetite, which supports the idea that differences in appetitive traits, in conjunction with environmental opportunities to overeat, influence weight gain in early childhood.

Genetic and environmental influences on infant growth: prospective analysis of the Gemini twin birth cohort

OBJECTIVE

Infancy is a critical period during which rapid growth potentially programs future disease risk. Identifying the modifiable determinants of growth is therefore important. To capture the complexity of infant growth, we modeled growth trajectories from birth to six months in order to compare the genetic and environmental influences on growth trajectory parameters with single time-point measures at birth, three and six months of age.

METHODS

Data were from Gemini, a population sample of 2402 UK families with twins. An average 10 weight measurements per child made by health professionals were available over the first six months. Weights at birth, three and six months were identified. Longitudinal growth trajectories were modeled using SITAR utilizing all available weight measures for each child. SITAR generates three parameters: size (characterizing mean weight throughout infancy), tempo (indicating age at peak weight velocity (PWV)), and velocity (reflecting the size of PWV). Genetic and environmental influences were estimated using quantitative genetic analysis.

RESULTS

In line with previous studies, heritability of weight at birth and three months was low (38%), but it was higher at six months (62%). Heritability of the growth trajectory parameters was high for size (69%) and velocity (57%), but low (35%) for tempo. Common environmental influences predominated for tempo (42%).

CONCLUSION

Modeled growth parameters using SITAR indicated that size and velocity were primarily under genetic influence but tempo was predominantly environmentally determined. These results emphasize the importance of identifying specific modifiable environmental determinants of the timing of peak infant growth.

Socioeconomic status and weight gain in early infancy

CONTEXT

The association between low socioeconomic status (SES) and childhood obesity foreshadows lifelong inequalities in health. Insight into the causal mechanisms linking childhood adversity to long-term health could be provided by discovering when the negative SES gradient in weight emerges and what early life experiences are associated with it.

OBJECTIVE

SES differences in infant weight gain in the first 3 months of life were examined, and contributions of parental body mass index, maternal smoking and feeding method to this association were assessed.

DESIGN

Observational study using longitudinal weight data from 2402 families taking part in the Gemini Study; a twin birth cohort recruited from all twin births between March and December 2007 in England and Wales.

OUTCOME MEASURES

Infant weights at birth and 3 months converted to standard deviation scores (SDS), change in weight SDS and rapid growth. SES was indexed by occupation and maternal education.

RESULTS

There were no SES differences in birth weight, but lower SES was associated with higher 3-month weight, greater change in weight and a higher prevalence of rapid growth (all P < 0.01), with graded associations across levels of SES. Including parental overweight or smoking in pregnancy in the regression model did not affect the association between SES and weight gain, but including feeding method attenuated the SES effect on weight gain by at least 62% and rendered it nonsignificant.

CONCLUSION

The foundations for lifelong socioeconomic inequalities in obesity risk may be laid in early infancy, with infant-feeding practices having a part in the diverging weight trajectories.

Nature and nurture in infant appetite: analysis of the Gemini twin birth cohort

BACKGROUND

A strong genetic influence on appetitive traits has been shown in children and adults, but no studies have examined appetite in early infancy, even though avidity of appetite has been linked with a higher risk of obesity.

OBJECTIVE

The objective was to investigate the heritability in early infancy of 4 appetitive traits that have been shown to be heritable later in childhood.

DESIGN

Data are from the Gemini Study, a population-based sample of twins (n = 2402 pairs) born in England and Wales in 2007. To describe their children's eating behavior during the first 3 mo of life while they were still exclusively milk fed, the parents of the twins completed 4 subscales of the Baby Eating Behavior Questionnaire: "enjoyment of food," "food responsiveness," "slowness in eating," and "satiety responsiveness." Heritability was estimated by using quantitative genetic model fitting.

RESULTS

Heritability was high for slowness in eating (84%; 95% CI: 83%, 86%) and satiety responsiveness (72%; 95% CI: 65%, 80%) and moderate for food responsiveness (59%; 95% CI: 52%, 65%) and enjoyment of food (53%; 95% CI: 43%, 63%).

CONCLUSIONS

Genetically determined variability in appetitive traits may be one of the pathways through which genes influence the growth rate in infancy. Early identification of infants with avid appetites may make it possible to implement strategies to attenuate the expression of these traits before excessive weight gain occurs.

Environmental influences on children's physical activity: quantitative estimates using a twin design

BACKGROUND

Twin studies offer a 'natural experiment' that can estimate the magnitude of environmental and genetic effects on a target phenotype. We hypothesised that fidgetiness and enjoyment of activity would be heritable but that objectively-measured daily activity would show a strong shared environmental effect.

METHODOLOGY/PRINCIPAL FINDINGS

In a sample of 9-12 year-old same-sex twin pairs (234 individuals; 57 MZ, 60 DZ pairs) we assessed three dimensions of physical activity: i) objectively-measured physical activity using accelerometry, ii) 'fidgetiness' using a standard psychometric scale, and iii) enjoyment of physical activity from both parent ratings and children's self-reports. Shared environment effects explained the majority (73%) of the variance in objectively-measured total physical activity (95% confidence intervals (CI): 0.63-0.81) with a smaller unshared environmental effect (27%; CI: 0.19-0.37) and no significant genetic effect. In contrast, fidgetiness was primarily under genetic control, with additive genetic effects explaining 75% (CI: 62-84%) of the variance, as was parent's report of children's enjoyment of low 74% (CI: 61-82%), medium 80% (CI: 71-86%), and high impact activity (85%; CI: 78-90%), and children's expressed activity preferences (60%, CI: 42-72%).

CONCLUSIONS

Consistent with our hypothesis, the shared environment was the dominant influence on children's day-to-day activity levels. This finding gives a strong impetus to research into the specific environmental characteristics influencing children's activity, and supports the value of interventions focused on home or school environments.