Only 9 (HST6, POLR3G, SLC6A20, ITGA2B, HOMER3, GMPR, AGBL1, CRABP2, OLFML2B) genes have been found to be shared between AD-PBMC, AD-Tissue, COVID-19-PBMC, and COVID-19-Tissue. Here, SLC6A20 is linked to Alzheimer disease.