Comorbidity of internalising and externalising disorders in a clinical sample of children with low IQ

Low IQ has been indicated to be a risk factor for the comorbidity of psychiatric disorders, although there is a paucity ofresearch in this area. The aim of the current study was to use latent class analysis to determine groups of children with distinct combinations, or classes, of internalising and externalising disorders. The data consisted of parent interview records of 310 children and adolescents (231 boys and 79 girls), referred to the Academic Child Psychiatry Unit (ACPU) of the Royal Children's Hospital, Melbourne. Participants were aged between 4 and 18 years with an IQ between 40 and 79. All were diagnosed with at least one of the internalising or externalising disorders. The results of the analysis revealed two underlying classes. Individuals in Class 1 had high levels of comorbidity across all of the internalising and externalising disorders, whereas individuals in Class 2 had high levels of comorbidity within the externalising disorders only. The patterns of comorbidity that were revealed contribute to the comorbidity research and to the taxonomic debate, and have important implications for clinical practice.