LGG carrying IDH-mutations split into the IDH-O (oligodendroglioma) group with co-deletions at Chromosome1p and Chr.19q (Chr1/19codel), the IDH-A and IDH-A’ (IDH-mut astrocytomas) groups without Chr1/19codel where IDH-A’ in contrast to IDH-A carries a deletion at Chr.19q. This evidence concerns the gene IDH1 and oligodendroglioma.