LRRC4B is a postsynaptic adhesion molecule that regulates excitatory synapse formation and maintenance. As a synaptic organizer, LRRC4B localizes to excitatory synapses and postsynaptic density membranes, where it mediates trans-synaptic cell-cell adhesion critical for synapse assembly 1. The protein functions through binding interactions with presynaptic partners; notably, FAM19A5 binds to LRRC4B to suppress spine density, and inhibiting this interaction increases spine density and synaptic strength 2. In neurodevelopmental disorders caused by SNAP25 variants, LRRC4B is among synaptic proteins significantly downregulated, contributing to reduced synaptic transmission 3. Beyond neurobiology, LRRC4B acts as a tumor-suppressive effector in breast cancer, suppressing cell proliferation by delaying cell cycle progression and modulating apoptosis 4. Additionally, LRRC4B expression is regulated by epigenetic mechanisms in atrial fibrillation, with DNA methylation disrupting transcription factor binding at this locus 5. These diverse functions suggest LRRC4B participates in both synaptic homeostasis and cellular growth control, making it relevant to neurological and oncological disease mechanisms.