Heritability of Psychological Traits and Developmental Milestones in Infancy: A Systematic Review and Meta-analysis

Abstract

Importance: Although infancy is the most rapid period of postnatal growth and development, factors associated with variation in infant traits are not well understood. Objective: To synthesize the large twin study literature partitioning phenotypic variance in psychological traits and developmental milestones in infancy into estimates of heritability and shared and nonshared environment. Data Sources: PubMed, PsycINFO, and references of included publications were searched up to February 11, 2021. Study Selection: Peer-reviewed publications using the classical twin design to study psychological traits and developmental milestones from birth to 2 years old were included. Data Extraction and Synthesis: Data were extracted in line with Preferred Reporting Items for Systematic Reviews and Meta-Analyses and categorized using the International Classification of Functioning, Disability and Health: Children and Youth Version. Data were pooled in 3-level random effects models, incorporating within-cohort variance in outcome measurement and between-cohort variance. Data were analyzed from March 2021 through September 2021. Main Outcomes and Measures: The primary outcomes were monozygotic and dizygotic twin correlations. These were used to calculate genetic and shared and nonshared environment estimates. Results: Among 139 publications that were systematically retrieved, data were available on 79044 twin pairs (31053 monozygotic and 47991 dizygotic pairs), 52 independent samples, and 21 countries. Meta-analyses were conducted on psychological traits and developmental milestones from 106 publications organized into 10 categories of functioning, disability, and health. Moderate to high genetic estimates for 8 categories were found, the highest of which was psychomotor functions (pooled h2, 0.59; 95% CI, 0.25-0.79; P