Preventable fraction of mental retardation: analysis based on individuals with severe mental retardation.

Reduction in the prevalence of mental retardation has been identified as a national goal since 1971. President Nixon proposed the year 2000 as a benchmark, by which time the prevalence of severe mental retardation should be reduced by as much as 50%. An analysis to determine the fraction of severe mental retardation that could be prevented with strategies currently available indicates that the goal will not be met. Knowledge of the causes of severe mental retardation is fundamental to developing prevention strategies. Increased diagnostic capability-clinical and laboratory-must be dramatically increased if a 50% reduction in the prevalence of severe mental retardation is to be achieved in the foreseeable future.