Prevalence of psychiatric diagnoses in children with mental retardation: data from a population-based study

The main purpose of the study was to estimate the prevalence of psychiatric diagnoses in children with mental retardation (MR) (IQ less than or equal to 70). All children born between 1980 and 1985 (N=30 037) in Akershus County, Norway, were screened for possible MR and assessed with either IQ tests or standardized developmental tests. A total of 178 children, 79 with severe mental retardation (SMR) (IQ<50) and 99 with mild mental retardation (MMR) (IQ 50 to 70) were included for further study, Psychiatric symptomatology was assessed as a standard part of the neurodevelopmental examination, which included a semistructured parent interview, a clinical child interview, and retrieval of the charts of previous child psychiatric examinations. Psychiatric diagnoses were classified according to the International Classification of Disease (ICD-10). In total, 65 (37%) of the total population with MR (95% confidence intervals 29 to 44) were registered to have psychiatric diagnoses, the most common being hyperkinesia (n=28) and pervasive developmental disorder (n=15). Psychiatric diagnoses were present in 42% of the population with SMR and 33% of the population with MMR (p=0.4). Of all children found to have a psychiatric diagnosis, approximately one-third had previously been examined by a child psychiatrist and indicated a previously unrecognized need for these services to children with MR.