We found in our study that the RALDH2 and RALDH3 genes, which encode main enzymes in the synthesis of RA, had significantly higher levels of transcription (from 4 to 250 times) in the NPC in both patients with PD compared to HD (Figure 6), which may be one of the reasons for the higher level of HOX gene expression. The gene discussed is ALDH1A3; the disease is Parkinson disease.