GJD3 encodes gap junction protein delta 3, also known as connexin 31.9 (Cx31.9) in humans or connexin 30.2 (Cx30.2) in mice, which forms transmembrane channels that allow low molecular weight materials to diffuse between adjacent cells 1. The protein plays a crucial role in cardiac conduction, specifically in atrioventricular node (AVN) function, where it facilitates electrical coupling between AV node cells and bundle of His cells 2. GJD3 is expressed in cardiac tissue beginning at embryonic day 12.5 and labels AVN cardiomyocytes and cardiac endothelial cells 2. In the inner ear, GJD3 is expressed in the organ of Corti and vestibular organs, particularly in the tectorial membrane and hair cell regions 1. Disease relevance includes associations with familial Meniere's disease, where rare missense variants may interfere with connexin assembly and gap junction formation 1. A protective missense variant (p.Pro59Thr) enriched in the Finnish population is associated with reduced varicose vein risk, suggesting GJD3 as a potential therapeutic target for venous disease 3. The gene has also been implicated in familial atrioventricular nodal reentrant tachycardia through calcium signaling pathways 4.