ALDH1A1 and Parkinson disease: Another potential explanation is the hypothesized loss of the dopaminergic phenotype of respective neurons in the SNpc, once a certain intracellular threshold of neuromelanin concentration is reached.[19, 44, 45] In contrast to that, the aged NMG proteome displayed an enrichment of proteins known to be associated with the dopaminergic pathway and PD: MAOA, MAOB, VPS35, and ALDH1A1, LRPPRC, and LONP1.