Psychiatric syndromes comorbid with mental retardation: differences in cognitive and adaptive skills

The study concerns the specific cognitive and adaptive skills of persons dually diagnosed with mental retardation (MR) and comorbid pathologies, as schizophrenia, personality and mood disorders, pervasive developmental disorders, epilepsy and ADHD. The sample was composed of 182 subjects, diagnosed as mild or moderate MR level, age range from 6 years 8 months to 50 years 2 months, mean age 17.1 (standard deviation 7.9). All the subjects were inpatients in a specialized structure for the diagnosis and the treatment of MR. The instruments of the study were Wechsler Intelligence Scale (WAIS-R or WISC-R according to the chronological age of subjects) and Vineland Adaptive Behavior Scale (VABS). Results confirm that comorbidity is a factor differentiating among mentally retarded subjects. Both verbal processes requiring memory retrieval and visuo-spatial processes are involved as differentiating features. ADHD strongly increases the impairment of cognitive skills, while behavioral disorders are less damaging in MR performance. In adult samples, the differentiating role of comorbid syndromes in MR individuals is reduced for cognitive skills, and limited to some basic verbal abilities, more impaired in mood disorder, less in schizophrenic disorder. The areas of adaptation and socialization, motor and daily living skills, are impaired more in generalized development disturbances than in comorbid schizophrenic and personality and mood disorders. An accurate psychological assessment of dual diagnoses is useful in detecting the specific underlying processes differentiating the comorbid syndromes, and in planning an appropriate rehabilitative treatment.