ALDH1A1 and Parkinson disease: The identified nominally significant alteration in “Retinol metabolism” matches with the observed change for the carotenoid retinal (see section “Catecholamine metabolism (retinal, ALDH1A1)”), while the changes for “Ubiquinone and other terpenoid-quinone biosynthesis” and “Tyrosine metabolism” may both reflect alterations in the network around the amino acid L-tyrosine, which is involved in both of these KEGG pathways and displays a nominally significant change in de novo PD vs. controls (p = 0.013).