The contribution of epidemiology to the understanding of neurodevelopmental disabilities.

Epidemiological approaches have played an important role in creating better understanding of developmental disabilities by delineating their frequency in populations and changes in their frequency over time, by identifying etiological factors, and by documenting pathways to prevention. Both cerebral palsy (CP) and mild intellectual disability are declining in frequency in high-income countries. The diagnosis of autism spectrum disorder has increased in recent decades, but much of this increase is a result of changing approaches to ascertainment and recording. Epidemiological studies have found that most CP is not of birth-asphyxial origin, that most febrile seizures do not pose a major risk for epilepsy, and that folic acid deficiency may contribute to developmental disabilities apart from its effect on neural tube defects. Epidemiological research has shown that an important fraction of neural tube defects and virtually all cases of Reye syndrome are preventable, and recent trials have shown ways to prevent CP. Early psychoeducational interventions in children at risk for mild intellectual disability are an effective and valuable societal investment. Very large population-based studies starting in pregnancy have been launched in Norway, Denmark, and Japan in recent years and these and other population studies promise to continue the epidemiological contribution to a better understanding of developmental disabilities.