Per the original definition, tissue HE is present when >1 of the following features is documented: (i) the percentage of eosinophils exceeds 20% of all nucleated cells in BM sections, (ii) a pathologist is of the opinion that tissue infiltration by eosinophils is extensive (massive) compared with “normal physiologic ranges,” or (iii) immunostaining reveals extensive extracellular deposition of eosinophil granule proteins, such as eMBP1 or EPX (Table 1).15 The gene discussed is EMBP1; the disease is hereditary elliptocytosis.