DNMT3A and Hydrocephalus: In addition, the incidence of hydrocephalus in Dnmt3a2−/− mice was 1% (2 out of 203), a 34-fold increase compared to the background level of 0.029% in the inbred C57BL/6J strain (https://www.jax.org/news-and-insights/2003/july/hydrocephalus-in-laboratory-mice), strongly implicating Dnmt3a2 loss as a contributing factor.