Acknowledging that ATRX mutations in IDH mutant diffuse gliomas almost never co-occur with 1p/19q codeletions and result in loss of immunohistochemical ATRX staining of tumor cell nuclei, an algorithm was proposed for a stepwise diagnostic approach that could reduce the number of molecular analyses needed for a final diagnosis: initial immunohistochemistry for ATRX and IDH1 R132H mutant protein, when necessary (e.g., in case of positive ATRX staining of tumor cell nuclei and negative staining for IDH1 R132H) followed by 1p/19q analysis and subsequently by IDH sequencing [96]. The gene discussed is IDH1; the disease is neoplasm.