Cerebral morphometric abnormalities in tourette's syndrome: A quantitative mri study of monozygotic twins

Although the pathologic substrate of Tourette's syndrome (TS) is unknown, studies have implicated subtle changes in the basal ganglia.To further investigate structural basal ganglia pathology in TS, we performed morphometric analyses of MRIs of 10 monozygotic twin pairs discordant for severity of TS but concordant for the presence of tic disorders (mean age, 16.3 years; range, 9 to 31 years). Right caudate volume was slightly but significantly reduced in the relatively more severely affected twins as a group compared with the less affected twins (mean difference equals 6%, p less than 0.01). Most of this difference was attributable to volume reduction in the anterior right caudate (p less than 0.02), which was smaller in the more severely affected twin in nine of 10 twin sets. The mean volume of the left lateral ventricle was 16% smaller in the more severely affected twins than in the less severely affected twins (p less than 0.01). The normal asymmetry of the lateral ventricles (left greater than right) was not present in the more severely affected twins, who had a trend toward a larger right lateral ventricle. Moreover, the difference within a pair in the degree of loss of the normal ventricular asymmetry correlated with the difference within a pair in the severity of the tic disorder (r equals 0.75, p less than 0.02). There were no other basal ganglia, ventricular volumetric, or asymmetry abnormalities. These findings partially replicate other MRI studies and suggest that subtle structural abnormalities in the CNS, particularly in the caudate, may play a role in the pathophysiology of TS. Because monozygotic twins are genetically identical, these structural abnormalities must reflect adverse environmental events. Traditional clinical correlations pertaining to hyperkinetic movement disorders have led most clinicians to presume that the primary pathology of Tourette's syndrome (TS) occurs in the basal ganglia, but there is relatively little data supporting this notion.The lack of evidence may relate to the paucity of neuropathologic investigations into TS. As more brain material has become available, investigators have begun to address this problem. Haber et al reported a decrease in dynorphin-like immunoreactive fibers in the globus pallidus in patients with TS, a finding that could reflect primary pathology in the striatum. Singer et al found an increase in dopamine uptake carrier sites in the striatum of patients with TS, once again focusing on the striatum as a crucial site of pathologic change in TS. Although noteworthy, these two unreplicated postmortem studies offer only a suggestion that an abnormality in the striatum may underlie TS.