Furthermore, HERV-W ENV downregulates 5-HT4 receptors and activates small-conductance calcium-activated potassium channels 2 and 3 (SK2/SK3), impairing hippocampal long-term potentiation and reducing neuronal excitability—mechanisms directly linked to cognitive deficits in schizophrenia [327,328,329,330]. The gene discussed is KCNN2; the disease is schizophrenia.