Third, patients with AD are usually comorbid with depressive disorder,[20] and previous 99mTc-TRODAT-1 SPECT studies suggest that DAT availability is higher in depressive subjects than in healthy controls.[32,33] Hence, major depression (MD) is one of the confounding factors in the investigation of DAT availability in patients with AD, but previous brain DAT imaging studies could not exclude these confounding factors.[10,11] In order to evaluate the influence of depressive effects on brain DAT activity, the present study recruited patients with AD/MD and pure AD. Here, SLC6A3 is linked to major depressive disorder.