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

OBJECTIVE

To investigate how the degree of prematurity interacts with genetic and environmental influences in their effect on verbal and nonverbal cognitive development.

STUDY DESIGN

The target sample consisted of more than 2000 pairs of twins born in England and Wales in 1994. At 24 months, measures of verbal and non-verbal cognitive development were obtained from the twins' parents. The sample was divided into 3 groups according to degree of prematurity: very preterm or high-risk (<32 weeks), moderately preterm or medium-risk (32-33 weeks), and mildly preterm/term or low-risk (>34 weeks). Quantitative genetic analyses were used to assess the contributions of genetic and environmental influences on vocabulary and cognitive development.

RESULTS

The results indicated gene-environment interactions. For the high-risk group, genetic effects on both verbal and non-verbal cognitive ability 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 responsible for cognitive outcomes of very preterm infants and suggest that early environmental influences appear to affect verbal and non-verbal cognitive development at 2 years of age.