Mismatch repair deficiency leading to a high number of mutations in microsatellites (MSI-H) has also been identified in numerous other tumor types, including a recently described subtype of IDH-mutant astrocytoma [111], and has subsequently been found in additional glioma subgroups, in the context of constitutional mismatch repair deficiency syndrome, Li–Fraumeni syndrome, Cowden syndrome, Lynch syndrome, or sporadically [53, 54]. The gene discussed is IDH2; the disease is astrocytoma (excluding glioblastoma).