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Tourette's syndrome in monozygotic twins. Relationship of tic severity to neuropsychological function.

OBJECTIVE
To determine whether there is a relationship between tic severity and neuropsychological function in Tourette's syndrome (TS).


DESIGN
The study employed a case-control series involving monozygotic twin pairs, divided into more severe and less severe groups based on tic severity and tested with a neuropsychological battery of tests.


SETTING
Twin pairs were recruited nationwide and evaluated in the National Institute of Mental Health Neuropsychiatric Research Hospital.


PATIENTS
Twelve twin pairs (mean age, 10.5 years; range, 8 to 16 years) in which at least one member met criteria for a diagnosis of TS.


RESULTS
Global neuropsychological performance was significantly worse in the twins with more severe tic symptoms, with significant differences emerging 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.


CONCLUSIONS
The results suggest that the nongenetic factors that influence tic severity in TS exert a similar effect on neuropsychological function, and that these two clinical manifestations of TS may share a common pathophysiologic state.