Dopamine uptake by platelet storage granules in first-degree relatives of Tourette’s syndrome patients

Background: Considering that platelets have been established to be good peripheral markers for the study of catecholaminergic neurons, we have applied an assay to measure the uptake of (3H)-dopamine (DA) into platelet storage granules (PSG). Recently, we reported that Tourette’s syndrome (TS) patients (pts) show decreased DA uptake into PSG. Methods: In the present study, 28 first-degree relatives (3 with chronic motor tics, 3 with transient tics, 6 with obsessive–compulsive behavior, and 16 without symptomatology) belonging to the families of 13 patients, and 14 unrelated healthy controls were studied. Results: Double reciprocal plots were constructed for each subject, and the apparent maximum velocity (Vmax) and Michaelis constant (Km) were determined by linear regression analysis (Lineaweaver–Burke plots). The uptake of DA (0.5–5 μmol/L) (mean ± SEM) by PSG from relatives with symptomatology was similar to the TS patients (symptomatic relatives Vmax 181 ± 22.2 fmol/mg protein, Km (μmol/L) 6.42 ± 0.29; TS pts Vmax 108 ± 6.9, Km 7.79 ± 0.64). Relatives without symptomatology on the contrary showed DA affinity characteristics similar to the controls (t test, paired t test, multivariate analysis of variance, and log transformation). Conclusions: The data presented suggest that TS is hereditary, but they do not distinguish between an autosomal dominant inheritance and a mixed or polygenic model.