Subtype-specific classifiers could improve accuracy; (3) combining FC with structural MRI (e.g., gray matter atrophy in basal ganglia) or biochemical markers (e.g., dopamine transporter availability) may enhance diagnostic precision; and (4) PD heterogeneity is a major challenge in neuroimaging research (Dorsey and Bloem, 2018), and subgroup-specific connectivity patterns are critical for personalized medicine. This evidence concerns the gene SLC6A3 and Parkinson disease.