Hypermutation as well as germline and somatic variants in MMR genes were recently observed in the spinal metastasis, also a gliosarcoma, of a patient with a low-grade glioma [52], suggesting that defects in both polymerase proofreading and MMR may promote hypermutation, metastasis to the spinal cord, and gliosarcoma development. Here, MRC1 is linked to gliosarcoma.