Repetitive and stereotyped behaviours in pervasive developmental disorders.

BACKGROUND: Repetitive and stereotyped behaviours are a heterogeneous group of behaviours present in many neuropsychiatric disorders. Despite their core significance in PDD, it is not clear whether there are distinct groups of these behaviours with different specificity to autism.
METHODS: A two-factor model of the repetitive behaviours, namely sensory/motor (lower-order) and cognitive rigidity (higher-order), was conceptualised. The model's goodness of fit to the data was examined in a clinic population of children with PDD, with and without mental retardation, and of those with only mental retardation (MR).
RESULTS: Subjects with PDD had higher rates of all repetitive behaviours compared to those with MR only. The existence of two independent 'lower-order' and 'higher-order' sub-groups of the repetitive behaviours was confirmed only in the MR group. The lower-order behaviours appear to be associated more with global developmental problems, whereas the higher-order behaviours were significantly associated with ruminations in the PDD group.
CONCLUSIONS: This study suggests that there may be two distinct sub-groups of repetitive behaviours whereby the sensory and motor repetitive behaviours are generally associated with lower developmental age and less specific to the autistic syndrome whereas the 'higher-order' behaviours may be a more 'autism specific' feature. The co-occurrence of the lower- and higher-order behaviours in PDD might reflect the end result of diffuse altered neural networks in these disorders thus being a specific feature of PDD. There is a need for more systematic studies of these behaviours not only in autistic disorders but also in other neuropsychiatric disorders.