Environmental influences on the developmental outcome of children at risk

The environment modulates the influence of reproductive and perinatal risk, and environmental risk and heritability must be considered in any developmental follow-up study. Biologic risk is influential in severe handicaps, but environmental variables are more important in mild mental retardation. Environment more strongly influences cognitive function than motor or neurologic function, and these effects become prominent by 18 to 24 months. The accumulation of risk factors, not a specific factor per se, has a negative impact; children at biologic risk are particularly vulnerable to negative environmental influences. These issues and their implications are discussed by drawing on representative historical and contemporary studies.