COMT and Mental deterioration: Consistent with previous reports which indicate that APOE, BDNF, and COMT polymorphisms may be implicated in cognitive decline (Bruder et al., 2005; Blom et al., 2009; Hashimoto et al., 2009; Schiepers et al., 2012), we expected that APOE, BDNF, and COMT polymorphisms would be associated with NIC instability (i.e., emerging impairment, NIC-to-MCI) and MCI stability (i.e., impairment chronicity, MCI-to-MCI) across the retest interval.