There is no consensus definition in the literature, but experience in the field suggests that this diagnosis is based on the workup detailed in Box 4 (including lymphocyte phenotyping to search for cell populations of interest in the case of lymphocytic HE/HES, and FIP1L1::PDGFRA testing only in the presence of suggestive clinical or laboratory findings). The gene discussed is FIP1L1; the disease is hereditary elliptocytosis.