The oligodendrocyte-specific G protein-coupled receptor GPR17 is a cell-intrinsic timer of myelination and in an MOG35–55-induced experimental autoimmune encephalomyelitis model of MS, the Olig1-regulated GPR17 is upregulated in OPCs in the lesion and blocks oligodendrocyte maturation by increasing Id2 and Id4 expression (Chen et al. 2009). The gene discussed is OLIG1; the disease is myeloid sarcoma.