The first two pathways consist of an IDH mutation followed by either a mutation of the tumor suppressor gene TP53 and loss of transcriptional factor ATRX to differentiate into an astrocytoma, or loss of heterozygosity of chromosomes 1p and 19q (1p/19q codel) to form an oligodendroglioma. The gene discussed is IDH2; the disease is astrocytoma (excluding glioblastoma).