Hereditary Elliptocytosis (HE) and Hereditary Pyropoikilocytosis (HPP)

Hereditary elliptocytosis (HE) is clinically heterogeneous disorder. The presence of elliptically shaped red cells on the peripheral blood smear is the characteristic feature of HE. HE patients can have a diverse spectrum of clinical findings ranging from life threatening anemias to asymptomatic carrier state (Lazarova et al., 2017). The inheritance of HE is autosomal dominant, with rare reports of recessive mutations. Homozygous and compound heterozygous HE variants present with moderate anemia and hemolysis (Delaunay, 2007; An and Mohandas, 2008). Weakened lateral linkages in membrane skeletons due to either defective spectrin dimer-dimer interaction or weakened spectrin-actin-protein 4.1R junctional complex results in the decrease of mechanical stability in these patients (Gallagher, 2004). Significant fragmentation of red blood cells in addition to the classic elliptocytes are a feature of the disease (see Figure 3). Newborn infants may show high level of red cell fragmentation, so called hemolytic HE (as seen in Figure 3A), which improves by age 1–2 years (as seen in Figure 3B; Palek and Lux, 1983; Mentzer et al., 1987; An and Mohandas, 2008). In the family with 4.1 deficiency, homozygotes had more severe disease than heterozygotes.

(A) Depiction of smear in left panel, Osmoscan in middle panel (blue line depicts a mild case, red line depicts a severe case), and EMA histogram in right panel in cases of hereditary elliptocytosis with severe fragmentation. (B) Changes in the EMA histogram in a HE patient with severe fragmentation at birth, and improvement 1 year later. (C) EMA in an older child showing a prominent left shoulder, but mostly resolved fragmentation.

Hereditary elliptocytosis cases show distinctive indented plateau on osmoscans pattern (Tchernia et al., 1981; Johnson and Ravindranath, 1996; Silveira et al., 1997). HE cells generate a trapezoidal profile in an osmoscan, with a normally positioned O_min and O_hyper but diminished EI_Max. The truncated curve reflects the inability of the already elliptical cells to deform further under shear stress. These findings were conformed in more recent work (Suemori et al., 2015) and has been re-appraised with the use of the new generation ektacytometers (Da Costa et al., 2016).

On EMA scans a bimodal pattern comprised of distinct population of cells with decreased MCF (representing fragmented cells) and a population with normal to high MCF may be present, especially in neonates. The EMA histograms reflect the level of fragmentation seen on smears. In infants who show high numbers of fragmented cells (“hemolytic HE”) two distinct populations one with low MCF and another with high MCF) can be identified (Figure 3A). Often in such cases the level of fragmentation decreases as the infant gets older and the EMA histograms reflect this with a decrease in the size of the red cell population with low MCF (Figure 3B). This feature also distinguishes hemolytic HE cases from cases of HPP where the extreme fragmentation gives a single population of cells with low MCF (Figure 4). In older children and adults the curve may overlap the control or shifted slightly to right but a trailing population of fragment cells can identified on the left shoulder of the curve (Figure 3C). This is an important finding as, it expands the value of the EMA test beyond the diagnosis of HS. In a recently reported work, heterogeneity in the ovalization of the HE patients had no association with EMA binding (Suemori et al., 2015).

Depiction of smear in, Osmoscan (blue line: HPP, black line: control, red/green line: father/mother), EMA histogram in cases of hereditary pyropoikilocytosis.

Hereditary pyropoikilocytosis (HPP), originally thought to be a unique and separate disease process, has been reclassified as a subset of HE due to double heterozygosity of mutations in the alpha-spectrin gene (Gallagher, 2004). This severe subset of HE-type disorders, in which red blood cells appear like those seen in thermal burn patients (Zarkowsky et al., 1975), is characterized by neonatal jaundice and transfusion dependent hemolytic anemia that persists through life. A peripheral smear shows microspherocytosis or micropoikilocytes more than elliptocytes. A protein analysis of the phospholipid bilayer of HPP reveals a mild spectrin reduction but a greater increase in spectrin dimer content than in common HE (Zarkowsky et al., 1975). We have seen 3 families with HPP phenotype. In one family despite the name of the disorder we were unable to show heat instability by morphology or circular dichroism studies in purified spectrin (Ravindranath and Johnson, 1985). Molecular studies (courtesy of Bernard Forget, Yale University) showed double heterozygosity for mutations near the dimer-dimer association site in alpha spectrin (Alpha1 74 c.28 CGT to CAT p.Arg > His and Alpha1 50a at c209 CTG > CCG, Leu to Pro). There was significant reduction in alpha spectrin. In these patients (n = 3) there was extreme cellular fragmentation and transfusion requirements abated only after splenectomy. We noted the lowest MCF values, with MCF 213.9 ± 52 in these cases, consistent with the MCV values of <50 fl. There is also a very clear change in the O_min and the deformability index was severely decreased (see Figure 5). The red cells in HPP appear to have a significantly decreased ability to maintain deformability in the face of hypotonicity, evidenced by their critical hemolytic value occurring at an osmolality much higher than normal controls and HS cases. These parameters distinguish HPP cases from common hemolytic HE especially in infants where the fragmentation could be mistaken for HPP. Both osmoscans and EMA test separate the two entities (see Tables 5, ​,66).

Depiction of smear in left panel, Osmoscan in center panel, and EMA histogram in right panel in cases of Southeast Asian ovalocytosis.

Hereditary elliptocytosis.

Hereditary pyropoikilocytosis.