IDH1 and oligodendroglioma: The 5th edition (2021) of WHO Classification of CNS Tumors shows that IDH-mutations are typical for diffuse lower grade astrocytomas (in the absence of 1p/19q codeletion and typically mutation in TP53 and/or ATRX) and oligodendrogliomas (with codeletion of chromosomal arms 1p and 19q).