Rather, they were pre-existing, resembling a case recently reported on by Ferris and colleagues, who reported a 1.8-fold increase in brain volume of a 2-year-old R222 RNaseT2 knockout rat with severe “spontaneous hydrocephalus.”22 The etiology of the “pre-existing” hydrocephalus (e.g., genetic) in rat #112 is unknown; another question is how a brain twice the volume of the normal brain could fit into the regular-sized skull. Here, RNASET2 is linked to Hydrocephalus.