APP and nervous system disorder: Based on the vital function of the HSA21 DEGs mentioned in the KEGG DISEASE database, these genes (COL6A1, COL6A2, COL18A1, APP, RCN1 and others) were closely related to some congenital malformations or genetic diseases, mainly for muscle and nervous system diseases (Myosclerosis, Alzheimer disease, Down syndrome, and others) (Figure 3D).