The interaction of prematurity with genetic and environmental influences on cognitive development in twins

Objective: To investigate how the degree of prematurity interacts with gene tic and environmental influences in their effect on verbal and non-verbal c ognitive development. Study design: The target sample consisted of more than 2000 pairs of twins born in England and Wales in 1994. Al 24 months, measures of verbal and non -verbal cognitive development were obtained from the twins' parents. The sa mple was divided into 3 groups according to degree of prematurity: very pre term or high-risk (<32 weeks), moderately preterm or medium-risk (32-33 wee ks), and mildly preterm/term or low-risk (>34 weeks). Quantitative genetic analyses Mere used to assess the contributions of genetic and environmental influences on vocabulary and cognitive development. Results: The results indicated gene-environment inter actions. For the high -risk group, genetic effects on both verbal and non-verbal cognitive abilit y were completely overshadowed by shared environmental factors, whereas for both medium- and low-risk groups, additive genetic effects explained 18%, to 33% of the variance. Conclusions: Our, findings indicate that genetic factors are not responsibl e for cognitive outcomes of very preterm infants and suggest that early env ironmental influences appear to affect verbal and non-verbal cognitive deve lopment at 2 years of age.