MTHFR and amyloidosis: Mild cognitive impairment (MCI) is a transitional cognitive stage between normal aging and dementia.1 Both lifestyle and genetic factors can play a role in the development of MCI.2,3,4 Apolipoprotein E polymorphism ε4 (APOE ε4) and methylenetetrahydrofolate reductase (MTHFR) TT genotype are well-recognized genetic risk factors for MCI and dementia.5,6,7 The status of APOE ε4 can contribute to the development of MCI by amyloid accumulation,8 whereas MTHFR TT genotype can mediate the level of homocysteine and vitamin B12 and folate concentrations, contributing to the incidence of MCI.9