The relationship between Tourette’s syndrome (TS) and chronic tic disorder was evaluated in 71 unselected children referred for psychopharmacological treatment at the Massachusetts General Hospital, Boston. Children with TS (32) and chronic tics (39) differed from controls in rates of comorbid psychiatric disorders including ADHD, obsessive-compulsive disorder, mood disorders (depression, bipolarity), antisocial disorders (conduct and oppositional defiant disorder), and anxiety disorders. Both TS and chronic tic groups also suffered from cognitive impairments, lowered academic achievement (WRAT arithmetic), arithmetic learning disabilities, and school dysfunction. TS patients differed from tic disorder patients in the significantly higher rates of obsessive-compulsive disorder, oppositional defiant disorder, and simple phobia. TS and chronic tic disorder are related disease entities, with TS being a more severe form of tic disorder. 
COMMENT. These findings are consistent with genetic studies showing that the TS gene is variably expressed as TS, transient tic disorders, or chronic tics. Comorbidity with ADHD, occurring in 50% of TS patients, is reported to cause more disability than the motor tics. The comorbidity with anxiety and mood disorders including mania affects the course, treatment, and outcome of tic disorders.