IDH1 and astrocytoma (excluding glioblastoma): Regardless of the overall frequency, the type of IDH mutations differs in the described tumor entities: in astrocytoma and oligodendroglioma, more than 90% of all IDH mutations are of the IDH1R132H type (3), whereas the second most frequent type (about 4% of mutations) is IDH1R132C. It has been suggested recently that natural selection may act against the rare IDH1R132 mutations in human glioma due to the cytotoxicity of high levels of D-2-hydroxyglutarate (D2HG) (11).