KCNH3 encodes Kv12.2, the pore-forming alpha subunit of a voltage-gated inwardly rectifying potassium channel characterized by fast activation during depolarization followed by rapid C-type inactivation, enabling inward rectification with rapid recovery from inactivation 1. KCNH3 is primarily expressed in the nervous system, where it can form heteromultimeric complexes with other Elk family members (KCNH8, KCNH4) but not with other potassium channel families 2. The channel regulates neuronal excitability and membrane potential through potassium ion transport and voltage-gated potassium channel activity. Pathogenic variants in KCNH3 cause neurodevelopmental disorders. A de novo missense variant (p.Ala371Val) identified in a patient with global developmental delay, intellectual disability, autism spectrum behaviors, insomnia, and nocturnal seizures produces loss-of-function through enhanced inactivation kinetics and dominant-negative effects on wild-type channels 3. Another de novo missense variant (A371V) similarly demonstrates voltage-dependent loss-of-function with accelerated inactivation and altered gating properties affecting neuronal firing behavior 4. Additionally, KCNH3 has been identified as a candidate gene in microcephaly-associated neurodevelopmental disorders 5. These findings establish KCNH3 as a disease gene for neurodevelopmental syndromes, distinct from its relatives KCNH2 (cardiac) and KCNH1, expanding the pathogenic KCNH gene family beyond previously characterized cardiac and neurological phenotypes.