Although there are a variety of different types of mutations in CDKN2A, including hemizygous deletion, missense, nonsense, frame-shift mutations, etc., these mutations are rare compared to CDKN2A deletion; evaluation of large lower-grade IDH-mutant glioma cohorts demonstrates a mutation rate of 0.8–3.7%, while homozygous deletion occurs in approximately 7–20% of these otherwise histologically lower-grade gliomas [12,18,21,22,23,24,25]. The gene discussed is IDH2; the disease is glioma.