HTR3A encodes the 5-hydroxytryptamine receptor 3A subunit, which forms serotonin-activated cation-selective ion channels that mediate fast depolarizing responses in neurons. The HTR3A receptor functions as a ligand-gated calcium channel, where serotonin binding leads to calcium influx and downstream signaling cascades 1. Mechanistically, HTR3A activation triggers Ca2+ influx, followed by CaMKIIα phosphorylation and NLRP3 inflammasome activation, demonstrating its role in inflammatory signaling pathways 1. The receptor shows significant disease relevance across multiple conditions. HTR3A polymorphisms are associated with psychiatric disorders, including bipolar disorder in Chinese populations and personality traits like harm avoidance in women 23. The gene also plays a role in gastrointestinal disorders, with specific polymorphisms linked to diarrhea-predominant irritable bowel syndrome 4. Additionally, HTR3A variants affect dopamine receptor availability in fibromyalgia patients, suggesting involvement in pain modulation 5. Clinically, HTR3A represents a therapeutic target, with antagonists used to treat emesis and IBS 6. The gene's polymorphisms may serve as biomarkers for psychotherapy response and are being investigated as predictors of treatment outcomes in psychiatric conditions 7.