ABCB1 and Alzheimer disease: Some studies also indicate that genetic variants of ABCA1 modify AD risk and tau- and Aβ-related pathogenesis [192]; however, other studies have demonstrated that several SNPs in the multi-drug resistance (ABCB1) gene (MRD1) (C1236T in exon 12, G2677T/A in exon 21, and C3435T in exon 26) do not show association with AD [193]; in contrast, ABCA2 has been reported to be a strong genetic risk factor for early-onset AD [194, 195].