GAP43 (Growth Associated Protein 43) is a membrane-associated protein that plays crucial roles in neuronal development, synaptic function, and brain circuitry regulation. The protein facilitates neuronal differentiation through RNA modification mechanisms, as FBLL1-mediated 2'-O-methylation of GAP43 mRNA promotes neuronal differentiation 1. GAP43 serves as a reliable biomarker for neuron-derived extracellular vesicles, being co-expressed with neuronal proteins β-III-tubulin and VAMP2 2. In synaptic dysfunction, GAP43 acts as a presynaptic marker whose levels correlate with glial reactivity in aging and Alzheimer's disease, with relationships mediated by phosphorylated tau 3. The protein critically regulates corticostriatal circuitry, as glutamatergic neuron-specific GAP43 knockout mice exhibit novelty-induced hyperactivity due to enhanced corticostriatal transmission and impaired endocannabinoid-mediated plasticity 4. Clinically, GAP43 expression correlates with functional outcomes in cancer treatment, where growing GAP43-positive nerves associate with denervation patterns in oropharyngeal cancer survivors 5. Additionally, GAP43 genetic variants show association with schizophrenia susceptibility in Chinese Han populations 6, and the protein facilitates mitochondrial transfer mechanisms that enhance glioblastoma tumorigenicity 7.