High-grade astrocytoma with piloid features (HGAP) is a recently described subtype of high-grade glioma that is characterized by a unique epigenetic signature, MAP kinase pathway activation (most often involving NF1, FGFR1, or BRAF) along with the combination of CDKN2A deletion and ATRX mutation, and an unfavorable clinical course intermediate between IDH-mutant gliomas and IDH-wildtype glioblastoma [23]. The gene discussed is IDH1; the disease is glioma.