In her second lecture, Zoghbi explains how MeCP2 molecularly modulates neuronal function. Their studies uncovered a critical link between cytosine methylation, MeCP2, and the methylating enzyme Dnmt3a, in Rett Syndrome. They hypothesized that MeCP2 partially causes Rett-Syndrome symptoms by failure of reading methylated DNA marked by Dnmt3 and indeed showed that Dnmt3-dependent mCH plays a central role in Rett pathogenesis.