When examining the relative quantity of each gene individually at the cross-sectional level, we demonstrated a similar transcriptional pattern for SKP1A, ALDH1A, PSMC4 and HSPA8 in the two PD cohorts compared to normal controls or AD groups, suggesting that these transcripts are altered at early stages of the disease and not affected by disease progression. This evidence concerns the gene HSPA8 and Alzheimer disease.