Inhibitory deficits in Tourette syndrome: A function of comorbidity and symptom severity

This study examined central inhibitory function in children with Tourette s yndrome (TS; N = 46) and normally developing controls (N = 22) matched on a ge, gender, and IQ. A negative priming task measured the ability to inhibit processing of irrelevant distracter stimuli presented on a visual display. Initial analyses indicated that participants with Tourette syndrome did no t differ significantly in inhibitory function from controls. However, when the large Tourette syndrome sample was separated into subgroups, one withou t evidence of comorbidity (N = 23) and the other meeting research criteria for either AD/HD, OCD, or both (N = 23), it became evident that individuals with Tourette syndrome with comorbid conditions tended to perform less wel l than the control group, whereas those without comorbidity performed much like controls. Similarly, when the large Tourette syndrome sample was divid ed into two subgroups on the basis of severity of symptomatology (N = 23 in each), those with more numerous and severe symptoms of Tourette syndrome, AD/HD, and OCD performed significantly less well than both controls and Tou rette syndrome subjects with fewer and less severe symptoms. This suggests that neuropsychological impairment occurs as a function of comorbidity and symptom severity in Tourette syndrome. It also suggests that categorical di agnoses alone may be less useful than dimensional methods for predicting co gnitive impairment in individuals with Tourette syndrome.