Co-expression analysis in non-neurological brains from the AHBA revealed several dopaminergic genes present in module M127. Their expression patterns were further investigated together with SNCA which is also known to regulate dopamine homeostasis25. GCH1, TH, and SLC6A3 (also known as DAT) were related to the functional term dopamine biosynthetic process, and SLC18A2 (also known as VMAT2) is known to store dopamine into synaptic vesicles26. Unlike SNCA, the expression of GCH1, TH, SLC6A3, and SLC18A2 was higher expressed in regions involved at preclinical stages than those involved at clinical stages (Fig. 6 and Supplementary Fig. 14). Furthermore, all these dopaminergic genes and SNCA showed a clear peak of expression in region R3 which includes the substantia nigra, basal nucleus of Meynert, and CA2-field.
