Erythrocyte-specific genes and genes involved in heme biosynthesis and iron metabolism, including erythrocyte membrane protein band 4.2 (EPB42), 5′-aminolevulinate synthase 2 (ALAS2), solute carrier family 4 member 1 (SLC4A1), glycophorin B (GYPB), solute carrier family 11 member 2 (SLC11A2), ferrochelatase (FECH), and hemochromatosis (HFE), were downregulated in PD studies (Supplementary Table S2). The gene discussed is FECH; the disease is Parkinson disease.