The relationship between tic severity and neuropsychological function was examined in 12 monozygotic twin pairs with Tourette’s syndrome at the National Institute of Mental Health, Bethesda, MD. Children with more severe tic symptoms had poorer overall performance on psychological tests, and differences were significant on individual tests of attention, visuospatial perception, and motor function. In each twin pair, the twin with more severe tics had poorer global neuropsychological function. 
COMMENT. Tic severity and psychological function in children with Tourette’s syndrome appear to be influenced by nongenetic factors with a common pathophysiology. The authors found that disturbances of attention were a cardinal psychological feature of TS, but most neuro-psychological measures were close to normal means.