Interaction of nutrition and genetics via DNMT3L-mediated DNA methylation determines cognitive decline

Low homocysteine levels and B vitamin treatment are reported to protect against declining cognitive health. Both B vitamins and homocysteine are involved in the production of S-adenosylmethionine, a universal methyl donor essential for the process of DNA methylation. We investigated the effect of a damaging coding variant within the DNA methyltransferase gene, DNMT3L (R278G, A/G) by examining B vitamin intake, homocysteine levels, cognitive performance, and brain atrophy in individuals in the VITACOG study of Mild Cognitive Impairment and the TwinsUK cohort. In the VITACOG study, individuals who received a two- year treatment of B vitamins and carried the G allele, showed better ‘visuospatial associative memory’ and slower rates of brain atrophy. In the TwinsUK study, improved ‘visuospatial associative memory’ was evident in individuals who reported regular vitamin intake and were A/A homozygotes. In silico modelling indicated that R278G disrupts protein interaction between DNMT3L and DNMT3A, affecting the DNMT3A-3L-H3 complex required for DNA methylation. These findings show that vitamin intake and genetic variation within DNMT3L interact to influence cognitive decline