Genome-wide association studies have identified genetic risks for obesity. These genetic risks influence development of obesity partly by accelerating weight gain in childhood. Research is needed to identify mechanisms to inform intervention. Cross-sectional studies suggest appetite traits as a candidate mechanism. Longitudinal studies are needed to test whether appetite traits mediate genetic influences on children's weight gain.
To test whether genetic risk for obesity predicts accelerated weight gain in middle childhood (ages 4-8 years) and whether genetic association with accelerated weight gain is mediated by appetite traits.
Longitudinal study of a representative birth cohort at the Trondheim Early Secure Study, Trondheim, Norway, enrolled at age 4 years during 2007 to 2008, with follow-ups at ages 6 and 8 years. Participants were sampled from all children born in 2003 or 2004 who attended regular community health checkups for 4-year-olds (97.2% attendance; 82.0% consent rate, n = 2475). Nine hundred ninety-five children participated at age 4 years, 795 at age 6 years, and 699 at age 8 years. Analyses included 652 children with genotype, adiposity, and appetite data.
Outcomes were body mass index and body-fat phenotypes measured from anthropometry (ages 4, 6, and 8 years) and bioelectrical impedance (ages 6 and 8 years). Genetic risk for obesity was measured using a genetic risk score composed of 32 single-nucleotide polymorphisms previously discovered in genome-wide association studies of adult body mass index. Appetite traits were measured at age 6 years with the Children's Eating Behavior Questionnaire.
Of the 652 genotyped child participants, 323 (49.5%) were female, 58 (8.9%) were overweight, and 1 (0.2%) was obese. Children at higher genetic risk for obesity had higher baseline body mass index and fat mass compared with lower genetic risk peers, and they gained weight and fat mass more rapidly during follow-up. Each SD increase in genetic risk score was associated with a 0.22-point increase in BMI at age-4 baseline (for the intercept, unstandardized path coefficient B = 0.22 [95% CI, 0.06-0.38]; P = .008. Children with higher genetic risk scores also gained BMI points more rapidly from ages 4 to 6 years (B = 0.11 [95% CI, 0.03-0.20]; P = .01 ; ? = 0.12) and from 6 to 8 years (B = 0.09 [95% CI, 0.00-0.19]; P = .05; ? = 0.10), compared with their lower genetic risk peers. Children at higher genetic risk had higher levels of alleged obesogenic appetite traits than peers with lower genetic risk at age 6 years, but appetite traits did not mediate genetic associations with weight gain. The sum of the 5 indirect effects was B = -0.001 (95% CI, -0.02 -0.01); P = .86; ? = 0.00.
Genetic risk for obesity is associated with accelerated childhood weight gain. Interventions targeting childhood weight gain may provide one path to mitigating genetic risk. However, middle childhood appetite traits may not be a promising target for such interventions. Studies of early-childhood samples are needed to test whether appetite traits explain how genetic risks accelerate growth earlier in development.