Cognitive functioning of juveniles with Down syndrome and other forms of mental retardation

The performance of juvenile Down syndrome individuals and two groups of oligophrenes was compared in several cognitive tests. All three groups of subjects were of the same CA, the Down's and one group of mentally retarded non-Down's had an average MA of 62, the other group an MA of 86 months. Though the group with the highest mental age usually outperformed the other two, significant differences were rare. It is concluded that at this age Down's and mentally retarded with different etiologies generally have rather similar cognitive abilities and that the intellectual deterioration of Down's, which at a later age inevitably leads to Alzheimer's disease, indeed starts only at a later CA.