Mechanistically, a case-control study proposed that elevated MMA might trigger immune cells to release factors such as tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), reactive oxygen species (ROS), and reactive nitrogen species (RNS); these factors, along with MMA itself, could potentially cross the blood-brain barrier and induce cognitive impairment (41). This evidence concerns the gene TNF and Cognitive impairment.