Of 205 patients with Tourette’s disorder in the North Dakota Longitudinal Tourette Syndrome Surveillance Project, 15 had comorbid bipolar disorder. The ratio of males to females was 5.2:1. The estimated risk of developing bipolar disorder among the study group of children and adolescents with Tourette’s disorder was more than four times higher than the level expected by chance, significant at the 0.05 level. Males were at greater risk than females, and adults had comorbid developmental disorders as well. Shared common neural pathways, especially basal ganglia structures, and genetic factors may explain the comorbidity. 
COMMENT. The authors have previously published case-reports of patients with comorbid Tourette’s disorder and bipolar disorder, some with early histories of attention deficit hyperactivity disorder. The frequency and intensity of motor and vocal tics were positively correlated with manic symptoms and inversely with depressive symptoms. Noradrenergic, dopaminergic, and serotonergic mechanisms have been invoked in all three disorders.