Emergence of a Gene x socioeconomic status interaction on infant mental ability between 10 months and 2 years

Abstract

Recent research in behavioral genetics has found evidence for a Gene × Environment interaction on cognitive ability: Individual differences in cognitive ability among children raised in socioeconomically advantaged homes are primarily due to genes, whereas environmental factors are more influential for children from disadvantaged homes. We investigated the developmental origins of this interaction in a sample of 750 pairs of twins measured on the Bayley Short Form test of infant mental ability, once at age 10 months and again at age 2 years. A Gene × Environment interaction was evident on the longitudinal change in mental ability over the study period. At age 10 months, genes accounted for negligible variation in mental ability across all levels of socioeconomic status (SES). However, genetic influences emerged over the course of development, with larger genetic influences emerging for infants raised in higher-SES homes. At age 2 years, genes accounted for nearly 50% of the variation in mental ability of children raised in high-SES homes, but genes continued to account for negligible variation in mental ability of children raised in low-SES homes.

Figure 1

Path diagram of the behavior genetic model (Model 3) fit to Bayley mental ability scores at 10 months and 2 years. This diagram represents one half of the model, i.e., one twin in each pair. A, C, and E are latent factors corresponding to additive genetic influences, environmental influences shared among twins (i.e. shared environment), and unique environmental influences (i.e. nonshared environment), respectively. The 0 subscripts denote the baseline wave of measurement (age 10 months), and the Δ subscripts denote the change between baseline and follow-up (age 2 years). Bayley scores at the second time point are modeled as a function of baseline scores plus change scores.

Figure 2

Age trends in mental ability scores for low, mean, and high levels of socioeconomic status (SES). Based on parameter estimates from Model 1. The Y axis on the right is in the original units of the BSF-R. The Y axis on the left has been scaled relative to mean and standard deviation of mental ability at 10 months.

Figure 3

Variance in longitudinal change in Bayley mental ability scores accounted for by genes (A), shared environment (C), and nonshared environment (E) according to SES. Based on parameter estimates from Model 3.

Figure 4

Variance in Bayley mental ability scores at each testing occasion accounted for by genes (A), shared environment (C), and nonshared environment (E) at low, mean, and high levels of socioeconomic status (SES). Derived from parameter estimates from Model 3.