In these three steps, mutations in isocitrate dehydrogenase (IDH) genes IDH1 and IDH2, alpha-thalassemia/mental retardation syndrome X-linked (ATRX) expression (nuclear ATRX is retained or lost) and possible co-deletions of 1p/19q (deletion of the short arm of chromosome 1 and the long arm of chromosome 19) are evaluated. The gene discussed is IDH2; the disease is alpha thalassemia spectrum.