Serra-Mestres et al. [24] compared 10 patients with TDs and 10 normal controls using SPECT technique and found that the density of dopamine transporters in the caudate nucleus and putamen of the TD group was higher than that in the control group, suggesting that abnormalities in dopamine transporters in the caudate nucleus and putamen are involved in the pathogenesis of TDs. The gene discussed is SLC6A3; the disease is thanatophoric dysplasia.