GADL1 (glutamate decarboxylase-like 1) is a pyridoxal-5'-phosphate-dependent decarboxylase localized to the cytoplasm that catalyzes the conversion of aspartate, cysteine sulfinic acid, and cysteic acid to β-alanine, hypotaurine, and taurine, respectively 1. Unlike classical glutamic acid decarboxylase, GADL1 exhibits no decarboxylation activity toward glutamate 1. The enzyme has tissue-specific expression patterns, peaking during early prenatal development in the brain, and is expressed exclusively in neurons rather than astrocytes 1. GADL1 plays critical roles in carnosine and β-alanine biosynthesis, with Gadl1-knockout mice demonstrating deficiency in these metabolites, particularly in the olfactory bulb, cerebral cortex, and skeletal muscle, accompanied by altered oxidative stress, energy metabolism, and anxiety phenotypes 2. Human genetic studies demonstrate strong associations between the GADL1 locus and plasma carnosine levels, subjective well-being, and muscle strength 2. GADL1 genetic variants (rs17026688, rs17026651) are significantly associated with lithium response in bipolar I disorder patients of Han Chinese descent, with sensitivity of 93% for predicting treatment response 3. Additionally, GADL1 overexpression suppresses cell migration through downregulation of migration-related genes and modulates immune responses and glycogen synthase kinase-3 signaling, which may underlie its role in lithium responsiveness 4, 5.