Research on Alzheimer's disease (AD), using the APP/PS1 mouse model and 13C-NMR metabolomics, has revealed a decrease in the lactate–alanine shuttle in the brain (Zhou et al., 2018), limiting the source of ammonia nitrogen from alanine that is used in the glutamate–glutamine cycle (Schousboe et al., 2003). The gene discussed is APP; the disease is Alzheimer disease.