Compared to the sporadic forms of IDH mutant gliomas, gliomas occurring in OD patients are also mainly diffuse and low-grade, and more frequently involve frontal lobes; conversely, they are diagnosed at an earlier age (26 vs. 44 years) and show higher rates of multicentric lesions (49% in our review) and brainstem localization (29%), and significantly lower rate of glioblastomas histotype (7%). The gene discussed is IDH2; the disease is glioblastoma.