USP18 and leukodystrophy: First, we will describe microgliopathies, which are white matter diseases believed to be caused primarily by microglial abnormalities (Prinz and Priller, 2014), including CSF1R-related leukodystrophy, Nasu–Hakola disease (NHD) related to recessive genetic variants in TREM2 and DAP12/TYROBP, and leukodystrophies related to recessive genetic variants in the LRRC33 (also known as NRROS) or USP18 genes.