KCNS3 encodes Kv9.3, a regulatory subunit of voltage-gated potassium channels that does not form functional channels independently but modulates delayed rectifier potassium channel activity when assembled into heteromeric complexes with KCNB1 (Kv2.1) 1. KCNS3-containing channels slow deactivation and inactivation kinetics, amplifying Kv2.1-mediated currents 1. In neurons, Kv2/KCNS3 heteromers comprise a distinct pharmacologically-separable conductance, particularly abundant in dorsal root ganglion neurons 2. KCNS3 is selectively expressed in parvalbumin-positive fast-spiking inhibitory neurons, where it is critical for their characteristic firing properties and participation in gamma-frequency oscillations 3. KCNS3 deficiency disrupts the precise timing of action potentials in these neurons, causing irregular spike trains and impairing gamma oscillation generation 3. Clinically, KCNS3 expression is significantly reduced (~23-40% lower) in prefrontal cortical parvalbumin neurons in schizophrenia patients, potentially contributing to impaired cognitive function and altered neural synchronization characteristic of the disease 43. Additionally, KCNS3 polymorphisms are associated with airway hyperresponsiveness in asthma 5, and specific variants show association with Parkinson's disease risk in Asian populations 6.