“He who sees things grow from the beginning will have the finest view of them” A systematic review of genetic studies on psychological traits in infancy

This paper reviews the studies that have aimed to identify genes influencing psychological traits in infancy (from birth to age 12 months). The review also addresses why genetic research in infancy is worthwhile and what genetic approaches such as genome-wide association studies and next generation sequencing could offer infant genetics. The results revealed that: (a) all studies (N = 26) have employed a candidate gene association design; (b) existing studies have most commonly focused on the Dopamine receptor D4 (DRD4) and the Serotonin transporter promoter (5-HTTLPR) gene polymorphisms; (c) phenotypes that have been assessed are temperament, attachment, and attention. Two further studies included both temperament and electrophysiological markers; (d) among many unreplicated findings, the most promising result appeared to be an association between the long DRD4 polymorphism and several “positive” temperament characteristics from birth to 4-months of age and at 12-months of age. It is concluded that, to date, there are limited, and mixed, findings regarding the possible association of genes with psychological phenotypes in infancy.