The epidemiology of mental retardation of unknown cause

Objective. To describe selected infant and maternal characteristics for children with mild and severe mental retardation (MR) of unknown cause. Study Design. Children with MR of unknown cause born in California between 1987 and 1994 were identified through service agency records and compared with the total population of California live births for selected characteristics recorded on the birth certificate. Results. For both children with mild and severe MR, risk was increased among males, low birth weight children, and children born to women of black race, older age at delivery, and lower level of education. Increased risk for mild MR was found for multiple births, second or later-born children, and children whose mothers were born outside of California. Increased risk for severe MR was observed among children born to Hispanic mothers; children born to Asian mothers also had increased risk for severe MR but decreased risk for mild MR. Conclusions. These results provide clues for understanding the underlying causes of MR and suggest that both biological and social factors are important.