DRD1 and Timothy syndrome: Studies have demonstrated that the abnormal activity of neurons in the striatum of the children with TS, the reduction in the volume of the caudate nucleus, and the activation of dopamine D1 (D1R) and dopamine D2 (D2R) receptors in the striatal output pathway resulting in excessive dopaminergic activity, which can enhance the motor activity of the thalamus-cortex (Wong et al., 2008).