Attempts have been made to establish objective diagnostic criteria for psychiatric disorders in persons with mental retardation. This paper describes the clinical features of the most important psychiatric disorders in mentally retarded adolescents: mood disorders, psychotic disorders, severe behavioral disorders, personality disorders, anxiety disorders, and attention deficit disorder with hyperactivity. The impact of mental retardation on personality development is confirmed by the high psychopathological vulnerability of the mentally retarded. All types of mental disorders can be observed, with an incidence estimated to be at least three or four times higher than in the general population. Adolescence is a particularly important phase for the mentally retarded, since adolescent turmoil can increase the risk of psychopathology.
Three of the DSM-IV (American Psychiatric Association, 1994) criteria for making a clinical diagnosis of mental retardation are consistent with the ICD-10 (World Health Organization, 1992): significantly sub-average intellectual functioning (at least two standard deviations below the norm, i.e., IQ less than 70); significant impairment in adaptive functioning; and onset before 18 years of age. The most frequently used criterion for classifying mental retardation is psychometric; persons are grouped on the basis of their intelligence quotient (IQ). DSM-IV and ICD-10 distinguish four levels of severity (mild, moderate, severe, and profound), which correspond to relatively differentiated clinical profiles.
Epidemiological estimates of the incidence of mental retardation in the general population vary--from 1% to 3% (Zigler & Hodapp, 1986)--due partially to differences in diagnostic criteria. There are significant differences in incidence for the mild and moderate forms of mental retardation when socioeconomic status is considered, while no differences are observed for the more severe forms. The male/female distribution is 1.5:1 (American Psychiatric Association, 1994).
Mental retardation has often been considered an intelligence disorder requiring principally pedagogical or social interventions. Its psychiatric dimension has been neglected. Thus, mental retardation can be considered the Cinderella of psychiatry (Potter, 1971).
The impact of mental retardation on personality development is confirmed by the high psychopathological vulnerability of the mentally retarded (Masi, Marcheschi, & Pfanner, 1996). According to the DSM-IV, all types of disorders are found in mentally retarded persons, with an incidence at least three or four times higher than in the general population. Rutter, Graham, and Yule (1970), in their epidemiological study on the Isle of Wight, found psychiatric problems in 30% to 42% of retarded children and adolescents, as opposed to 7% of the children with normal intelligence levels. Rates were similar among noninstitutionalized samples in the United States and Sweden (Chess, 1971; Gillberg, Persson, Grufman, & Themmer, 1986; Reiss, 1990).
Adolescence is a particularly important phase for the mentally retarded, because intellectual impairment can reduce adolescents' ability to integrate bodily and psychic transformations, increasing the risk of psychopathology. The clinical characteristics of psychiatric disorders in mentally retarded adolescents are influenced by the intellectual disability. Since clinical features are often not well defined and symptoms are more aspecific as the intellectual impairment becomes more severe, diagnosis can be particularly difficult. In addition, the course of mental disorders often differs for the mentally retarded; for example, reversibility is less frequent. The role of traumatic life events is especially important, since they more frequently have a triggering effect than for those with normal intelligence. The issue of psychopharmacological therapy is complex, as mental retardation has been considered an exclusion criterion in most studies on the efficacy of psychotropic drugs (Masi, Marcheschi, & Luccherino , 1996). …