RPL21 and Alzheimer disease: And PCA found many ribosomal proteins: LOC653737/LOC728501/LOC729402/LOC731567/RPL21, RPL29, RPL30, LOC342994/LOC651249/LOC729536/RPL34, RPL35, RPL4, RPL9, RPS10, RPS11, that were all down-regulated in severe AD, except one gene RPL13 that was up-regulated.