CHR4 encodes the alpha-9 subunit of nicotinic acetylcholine receptors (nAChRs), which function as pentameric, ligand-gated cation channels with high calcium permeability 1. The gene is located on chromosome 4.1-p14 and contains five exons separated by four introns 1. CHR4 forms either homopentamers or heteropentamers with CHR4, creating calcium-permeable channels that mediate synaptic transmission in the inner ear between efferent olivocochlear fibers and hair cells 1. Beyond auditory function, CHR4 is expressed in various cell types including lymphocytes, keratinocytes, and B cells 23. The receptor plays important roles in skin homeostasis, where B cell-derived acetylcholine binding to CHR4 on keratinocytes reduces proliferation and controls inflammation 3. Clinically, CHR4 has significant disease relevance in cancer, particularly triple-negative breast cancer (TNBC), where it promotes tumor proliferation, enhances stemness properties, and suppresses ferroptosis through AKT, ERK, and STAT3 pathways 4. CHR4 polymorphisms interact with smoking exposure to increase breast cancer risk 5, and high expression correlates with poor survival outcomes 6. The receptor is also upregulated in psoriasis, correlating with disease severity scores 7.