Decreased levels of amino acids have been shown to be sensed by the integrated stress response (ISR) pathway that activates pro‐longevity genes (e.g., FGF21).[37] However, the active ISR pathway has also been linked to cognitive decline in aging.[40] Inhibition of ISR improved cognitive functions and was accompanied by decreased expression of Rtp4 in hippocampal samples of aged mice.[40] Interestingly, downregulation of Rtp4 is mimicked by PTS supplementation in our study (Figure 2B). The gene discussed is FGF21; the disease is Mental deterioration.