MAPT and Alzheimer disease: Valine correlated negatively with pTau181, suggesting a mitigating role against tau phosphorylation, while Leucine showed negative trends with amyloid ratios, consistent with reports that BCAAs regulate neurotransmitter synthesis, glutamate excitotoxicity, and mTOR signaling to influence synaptic plasticity and neuronal survival.70,71 In summary, our findings delineate a multifaceted biochemical landscape in AD that integrates fatty acid oxidation, glycolysis, one-carbon metabolism, oxidative stress, purine turnover, dietary influences, and genetic susceptibility.