PRDM9 and Cognitive impairment: Because we identified a concomitant reduction in mRNA expression of histone methyltransferases (Kmt2a, Kmt2b, Kmt2d, and Setd1a) and H3K4me2 protein, we investigated whether pharmacological inhibition of LSD1 normalizes the epigenetic, behavioral, and cognitive deficits in mice expressing HERV-W ENV.