Clinical assessment of 4500 developmentally delayed individuals.

Data collected on 4500 developmentally delayed clients and classified according to a modification of Heber's criteria are presented. Statistically significant associations between variables are described. Although such associations are not necessarily biologically meaningful on this evidence alone, they are presented for comparison with other data collections and to suggest areas of further investigation. An examination is made of data relating to mental retardation of unknown cause compared with mental retardation of known causes. The unknown group most resembles those with metabolic disease and least resembles those with chromosome aneuploidy. The data also suggest that mental retardation secondary to brain injury is uncommonly associated with evidence of genetic predisposition.