The proposed algorithm is based on our observation that ATRX loss was 100% specific to the astrocytic phenotype, which confirms the data repeatedly reported in the literature [2, 13, 21], and that the co-occurrence of retained ATRX and loss of H3K27me3 in IDH-mutant gliomas was 100% specific to oligodendroglial phenotype. The gene discussed is ATRX; the disease is glioma.