The fact that efficient re-myelination in chronic MS patients depends largely on the ability of post-mitotic OPCs to up-regulate RxRγ at lesions, and OPC culture treatment with RxRγ antagonists leads to impaired OPC maturation [21], supports the view that these findings can be extended to premyelinating OLs. The gene discussed is RXRG; the disease is myeloid sarcoma.