In conclusion, we found that: (a) GPR17 receptor is widely expressed in oligodendroglial cells in MS subjects; (b) it mainly localizes to inflamed areas of WM; (c) in ALs, GPR17 is predominantly expressed by oligodendroglial cells with rounded morphology reacting against a demyelinating damage, whereas in NAWM there is a balance between ramified and rounded morphology. The gene discussed is GPR17; the disease is myeloid sarcoma.