Among the detected PD-specific co-expression modules, only the purple module detected in BA9 of the prefrontal cortex which is the most PD-specific module (Supplementary Figure S5) was significantly correlated with the light cyan module of AD APOE ε4 non-carriers with an extremely low P-value (Figure 7A, P = 9.522 × 10-24, Supplementary Table S26 for detailed overlapped genes). This evidence concerns the gene APOE and Alzheimer disease.