COMORBID TOURETTES-DISORDER AND BIPOLAR DISORDER - AN ETIOLOGIC PERSPECTIVE

Objective: Using an epidemiologic approach, the authors attempt to elu cidate relationships between Tourette's disorder and bipolar disorder. Method: Of 205 patients with Tourette's disorder in the North Dakota Longitudinal Tourette Syndrome Surveillance Project, 15 had comorbid b ipolar disorder. A subset of the patients with Tourette's disorder had been included in earlier population-based prevalence studies of Toure tte's disorder in children, adolescents, and adults. Minimal risk rati os were calculated for the patients with Tourette's disorder plus bipo lar disorder by age group (children/adolescents and adults). This info rmation was used to estimate genetic risk indicators for comorbid Tour ette's disorder and bipolar disorder. Results: The estimated risk of d eveloping bipolar disorder among the study group of children, adolesce nts, and adults with Tourette's disorder was more than four times high er than the level expected by chance, but this finding did not reach s tatistical significance. It was indicative of trends, however. Conclus ions: Comorbidity between Tourette's disorder and bipolar disorder doe s not appear to be due to chance co-occurrence of the two disorders. A lthough a genetic mechanism may play a casual role, in the absence of family studies an explanatory model involving the concept of canalizat ion of basal-ganglia-mediated dysfunctions is offered. In such a const ruct, Tourette's disorder would be a likely accompaniment to other con ditions, including bipolar disorder, whose pathogenic determinants mig ht channel through neural pathways involving the basal ganglia. The pr esence of significant developmental disabilities may further enhance f actors culminating in comorbid Tourette's disorder and bipolar disorde r.