LRFN1 (leucine rich repeat and fibronectin type III domain containing 1) is a neuronal transmembrane glycoprotein that plays a central role in excitatory synapse development and maintenance. The protein contains characteristic leucine-rich repeat, immunoglobulin-like, and fibronectin type III domains, with an extracellular N-terminus and intracellular C-terminus 1. LRFN1 promotes neurite outgrowth in hippocampal neurons and regulates excitatory synapse assembly through binding PSD95 at the postsynaptic density, facilitating clustering of key postsynaptic proteins including DLG4, DLGAP1, GRIA1, and GRIN1. Expression begins during immature neural development and persists into adulthood, predominantly in brain tissue 1. Beyond its synaptic functions, LRFN1 demonstrates emerging roles in cancer biology and disease pathology. In clear cell renal cell carcinoma, LRFN1 is directly targeted by miR-187-3p, and elevated LRFN1 expression promotes tumor progression, enhances immune infiltration (including M2 macrophages and CD8+ T cells), and serves as an independent prognostic biomarker 2. LRFN1 has been identified as a component of prognostic signatures in ovarian cancer and salivary gland carcinomas, where mutations associate with tumor subtype classification 3, 4. Additionally, LRFN1 methylation patterns are affected by maternal smoking exposure in utero 5. While LRFN1 localizes to a chromosome 19 region associated with autosomal dominant partial epilepsy with auditory features, sequence analysis has not identified disease-causing mutations in this gene 6.