["The Journal of Physiology, Volume 604, Issue 8, Page 3413-3430, 15 April 2026. ", "\nAbstract figure legend Potassium‐selective KV1.2 channels are encoded by the KCNA2 gene and regulate electrical signalling in neurons. KCNA2 genetic variants are associated with epileptic and developmental encephalopathy. We characterized two variants that subtly alter the channel's amino acid composition, p.H310D and p.G318D. They share several similarities: they occur in proximal and highly conserved positions; they both result in aspartate substitution; and they both prevent the surface‐trafficking of KV1.2 subunits, causing loss of KCNA2 function. Each KV1.2 channel is made of four subunits, and in heterozygous individuals both wild‐type and variant subunits coexist and may interact. p.H310D was a strongly negative‐dominant variant, as KV1.2(H310D) subunits suppressed the surface trafficking of wild‐type KV1.2 subunits. In contrast, KV1.2(G318D) subunits barely influenced the trafficking of wild‐type KV1.2 subunits. Since the p.G318D patient nevertheless has neurological symptoms, this suggests that the activity of one wild‐type KCNA2 allele is not enough; that is KCNA2 may be a haploinsufficient gene in humans.\n\n\n\n\n\n\n\n\n\nAbstract\nKCNA2 encodes the pore‐forming subunits of the voltage‐gated, potassium‐selective channel KV1.2, which controls the excitability of both central and peripheral neurons. Either gain‐ or loss‐of‐function KCNA2 variants can cause severe neurological disease, assigned developmental epileptic encephalopathy (DEE) type 32. Here, we report and characterize two apparently similar variants, p.H310D and p.G318D, both discovered in patients with global developmental delay and involving aspartate substitutions at positions highly conserved in the KV‐channel superfamily. We found that both are loss‐of‐function variants, completely abolishing channel current and subunit trafficking. Channel constructs of KV1.2‐variant subunits in tandem with KV1.4 had a conductance with inhibited voltage‐dependence, with shifted half‐activation potentials by 27 and 19 mV for p.H310D and p.G318D, respectively. p.H310D was strongly negative‐dominant: heterozygous cells exhibited only 7% conductance relative to homozygous wild‐type, while only half of wild‐type subunits could traffic to the surface. In contrast, p.G318D exhibited weaker negative dominance, with 32% conductance in heterozygous cells and 86% wild‐type‐subunit trafficking. Taken together with the p.G318D‐patient's neurological symptoms, the latter suggests that KCNA2 is a haploinsufficient gene in humans.\n\n\n\n\n\n\n\n\n\nKey points\n\nKCNA2 encodes the pore‐forming subunits of the KV1.2 voltage‐activated, K+‐selective ion channel, which regulates electrical signalling in neurons. We characterized two KCNA2 variants from patients with global developmental delay.\nBoth variants are aspartate substitutions of proximal, highly conserved positions in KV‐channels: p.H310D and p.G318D.\nIn frog oocytes and in primate cells, both variants cause loss of KCNA2 function, abolishing currents and surface trafficking, and inhibiting channel voltage‐dependent opening.\np.H310D is strongly negative‐dominant, potently suppressing wild‐type subunit functional expression.\nIn contrast, p.G318D is weakly negative‐dominant, leaving wild‐type subunits largely unaffected. This suggests that KCNA2 is a haploinsufficient gene in humans.\n\n\n"]