Diffusion MRI studies in moderate-severe brain-injured patients displayed reduced substantia nigra volume, and striatal DAT levels associated with cognitive deficits in information processing speed and executive functions [81], with the potential to influence symptoms associated with attention-deficit/hyperactivity disorder (ADHD), Parkinson’s disease (PD) and Huntington’s disease (HD). Here, SLC6A3 is linked to Parkinson disease.