IDH1 and central nervous system cancer: However, not all IDH-mutant gliomas, especially the non-canonical IDH mutant gliomas (about 20–25% of grade-2 and 5–12% of grade-3 gliomas), show the neomorphic activity of 2HG production [25], suggesting that 2HG detection alone may not always be sufficient for identifying the IDH mutation in gliomas.