Birth weight modifies the association between central-nervous-system gene variation and adult body mass index

Genome wide association studies (GWAS) have identified approximately 100 loci associated with body mass index (BMI). Persons with low birth-weight have an increased risk of metabolic disorders. We postulate that normal mechanisms of body weight regulation are disrupted in subjects with low birth-weight. The present analyses included 2215 African American women from the Black Women’s Health Study, and were based on genotype data on twenty BMI-associated loci and self-reported data on birth-weight, weight at age 18, and adult weight. We used general linear models to assess the association of individual SNPs with BMI at age 18 and later in adulthood within strata of birth-weight (above and below the median, 3200 g). Three SNPs (rs1320330 near TMEM18, rs261967 near PCSK1, and rs17817964 in FTO), and a genetic score combining these three variants, showed significant interactions with birth-weight in relation to BMI. Among women with birth-weight <3200 g, there was an inverse association between genetic score and BMI; beta-coefficient = −0.045 (95% CI −0.104, 0.013) for BMI at age 18, and −0.055 (95% CI −0.112, 0.002) for adult BMI. Among women with birth-weight ≥3,200 g, genetic score was positively associated with BMI: beta-coefficient = 0.110 (95% CI 0.051, 0.169) for BMI at age 18 (P for interaction = 0.0002), and 0.112 (95% CI 0.054, 0.170) for adult BMI (P for interaction < 0.0001). Because TMEM18, PCSK1, and FTO are highly expressed in the central nervous system (CNS), our results suggest that low birth-weight may disrupt mechanisms of CNS body weight regulation.