Genetic and Environmental Influences on Developmental Milestones and Movement: Results from the Gemini Cohort study

Purpose: Variability in the timing of infant developmental milestones is poorly understood. We used a twin analysis to estimate genetic and environmental influences on motor development and activity levels in infancy. Method: Data were from the Gemini study, a twin birth cohort of 2402 families with twins born in the UK in 2007. Parents reported motor activity level for each of the twins at age 3 months using the Revised Infant Behavior Rating Scale (IBQ-R), and also reported the age at which they first sat unsupported, crawled, and walked unaided. Results: Activity level at 3 months, and age of first sitting and crawling were about equally influenced by the shared family environment (45%-54%) and genes (45%-48%). Genetic influences dominated for the age of taking first independent steps (84%). Conclusion: Aspects of the shared family environment appear to be important influences on motor activity levels and early milestones, although the timing of walking may have a stronger genetic influence. Further research to identify the specific environmental and genetic factors that promote early activity may be important for longer-term health outcomes.