SLC6A3 and Parkinson disease: It has been reported that miR-133b is downregulated in the midbrain of PD patients, which indirectly decreases the expression of vesicular monoamine transporter 2 (VMAT2) by downregulating paired-like homeodomain transcription factor 3 (Pitx3) and altering the expression of dopamine transporter (DAT) through the same process that alters VMAT2 expression (Hwang et al., 2009).