Advances in genetic research reveal that complex human traits are influenced by many genes, each having very small effects. To take account of the multiplicity of genetic influences, statistical models derived from genome-wide association studies (GWAS) are used to aggregate genetic factors associated with particular traits into polygenic scores for those traits.

Two such traits are adult schizophrenia and level of adult educational attainment. In order to determine whether phenotypic precursors of these traits could be detected in childhood, Jansen et al. (2018) tested associations between children’s polygenic scores (derived from genetic assays of the children’s blood) and problem scales scored from the CBCL/1½-5 and CBCL/6-18 at ages 3, 6, and 10. The children were participating in the Generation R (R = Rotterdam, The Netherlands) longitudinal study that began with thousands of pregnancies.

At age 3, children with high polygenic scores for schizophrenia obtained exceptionally high scores on the CBCL/1½-5 Emotionally Reactive syndrome, while at age 10, they obtained exceptionally high scores on the CBCL/6-18 Thought Problems syndrome. By contrast, children with high polygenic scores for educational attainment obtained exceptionally low scores on most problem scales, especially on the Attention Problems syndrome at ages 3, 6, and 10. Well before the children might manifest signs of adult schizophrenia and well before they would reach their highest level of educational attainment, CBCL scores were thus identified as phenotypic expressions of genetic influences on eventual schizophrenia and educational attainment.

The authors concluded that their “study shows that genetic predispositions for psychiatric disorders and educational attainment are associated with early behavioural problems. These associations were present throughout early childhood and at an earlier age than described in most previous studies” (p. 45).

Reference: Jansen, P.R. et al. (2018). Polygenic scores for schizophrenia and educational attainment are associated with behavioural problems in early childhood in the general population. Journal of Child Psychology and Psychiatry, 59, 39-47.