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. This evidence concerns the gene MRC1 and central nervous system cancer.