HE and HPP. The most common form of HPP, diagnosed in infants with neonatal hyperbilirubinemia, is due to an SPTA1 HE-causing mutation in trans to the intronic SPTA1 variant c.6531-12C>T known as α^LELY (low-expression LYon). Familial studies at the time reveal that 1 parent carries the SPTA1 HE-causing mutation and has elliptocytosis (smear characterized by elliptically shaped red blood cells), while the other parent carries α^LELY with a normal erythrocyte phenotype. The blood smear in HPP is characterized by marked anisocytosis and poikilocytosis with bizarre microcytes and fragmented cells along with elliptocytes (scale bars, 14 µm; Wright-Giemsa stain). HPP RBCs were found early on to have increased thermal sensitivity; this is maybe the source of the name pyro (coming from the Greek word “πυρ” meaning fire)-poikilocytosis. Another possibility for the origin of the term is that the cells resemble the morphology of the blood smear in patients with the microangiopathic hemolytic anemia of patients with extensive burns.