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Abstract

Developmental and epileptic encephalopathies (DEEs) represent rare but severe neurological conditions that place immense burdens on affected patients and their families. In 2015, we identified DEE patients with variants in KCNA2, a gene that encodes the voltage-gated potassium channel subunit KV1.2.1 DEE patients with KCNA2 loss-of-function (LOF) variants predominantly experience focal epileptic seizures.1 We recently generated a Kcna2+/P405L knock- in mouse model to understand both epileptogenic and compensatory effects for this LOF variant. We performed metabolic and behavioral phenotyping, intracranial video EEG monitoring, as well as patch clamp recordings from acute slices. Brains of mice aged P62-112 that previously underwent EEG were cut in coronar slices and stained against KV1.2 and Caspr to identify the paranodal region of nodes of Ranvier and c-Fos and NeuN to detect the unknown origin of focal seizures caused by this variant. Furthermore, we performed Golgi stainings for spine morphology. All Kcna2+/P405L mice with C57Bl/6 background died prematurely between one and two months of age, while roughly half of Swiss Kcna2+/P405L mice showed normal survival. In general, Kcna2+/P405L mice showed a slight hyperactivity, with males exhibiting underweight tendencies. Notably, during EEG recordings heterozygous Kcna2+/P405L mice exhibited focal and bilateral tonic-clonic seizures. We found significantly increased c-Fos expression in primary motor and somatosensory cortices and the hippocampus in brains of mutant animals. The distribution of channels including KV1.2 subunits at nodes of Ranvier was not different for Kcna2+/P405L animals compared to their wildtype littermates. Firing frequency of cortical pyramidal cells was similar to wildtype and the only difference in intrinsic properties was a significant increase in the afterhyperpolarization amplitude. To conclude, Kcna2+/P405L mice presented focal seizures and increased mortality. The origin of these seizures might lie in the cortex, since seizures often evolved from motor to bilateral tonic- clonic ones but is likely not driven by increased excitability of pyramidal neurons. In addition, Kcna2+/P405L mice were hyperactive, and males displayed underweight. 1 Syrbe S, Hedrich UBS et al. (2015). De novo loss- or gain-of-function mutations in KCNA2 cause epileptic encephalopathy. Nature genetics.