Theference collected substantial knowledge on mental retardation. It focused on the aspects which have major relevance to the daily practice of the primary physician. Lest we gain the impression that most problems concerning mental retardation have been resolved, we turn our attention now to the unresolved issues. Dr. Gardner has presented the psychosocial and educational aspects. My focus is on those topics which have a stronger biomedical component. I have selected five subject areas which I expect will gain in importance during the next decades.
A Problem in Epidemiology
It is often stated, on the basis of reasonably hard data, that 3% of the newborn will develop as mentally retarded individuals. It is estimated that (1) once in 1,000 a child is born whose IQ will not exceed 20; (2) the birth frequency of children with IQs between 20 to 50 is four times higher; and (3) 25 of 1,000