FGF13 is a non-secreted intracellular fibroblast growth factor that functions primarily as a cytoplasmic and nuclear regulator of neuronal physiology 1. As a microtubule-binding protein, FGF13 stabilizes microtubules and regulates axonal development and neuronal polarization 1. A critical function involves regulating voltage-gated sodium channel (Nav) activity through direct protein-protein interactions with Nav channels, particularly at the axon initial segment 23. FGF13 interacts with the MAPK scaffolding protein IB2 and modulates mitochondrial anchoring through binding to mitochondrial proteins like MCH2, preventing release of damaged mitochondria 41. Beyond neurology, FGF13 regulates adipocyte mitochondrial function and glucose homeostasis, with obesity-induced FGF13 expression impairing metabolic health 5. Clinically, FGF13 mutations cause developmental and epileptic encephalopathy 90 and X-linked intellectual disability 6. Recent evidence associates FGF13 with autism spectrum disorder susceptibility through X-chromosome X, with sex-specific allele frequency differences 7. FGF13 dysregulation contributes to Parkinson's disease pathology through impaired mitochondrial control of neuroinflammation 4. In diabetic neuropathy, elevated FGF13/Nav1.7 ratios promote nociceptive signaling, making FGF13 a therapeutic target for pain management 3. These diverse functions position FGF13 as a multi-system regulator with significant disease relevance across neurological, metabolic, and pain pathways.