Dehydrated hereditary stomatocytosis (DHS), also known as hereditary xerocytosis, is an autosomal dominant hemolytic anemia characterized by primary erythrocyte dehydration. DHS erythrocytes exhibit decreased total cation and potassium content that are not accompanied by a proportional net gain of sodium and water. DHS patients typically exhibit mild to moderate compensated hemolytic anemia, with an increased erythrocyte mean corpuscular hemoglobin concentration and a decreased osmotic fragility, both of which reflect cellular dehydration (summary by Zarychanski et al., 2012). Patients may also show perinatal edema and pseudohyperkalemia due to loss of
K+ from red cells stored at room temperature. A minor proportion of red cells appear as stomatocytes on blood films. Complications such as splenomegaly and cholelithiasis, resulting from increased red cell trapping in the spleen and elevated bilirubin levels, respectively, may occur. The course of DHS is frequently associated with iron overload, which may lead to hepatosiderosis (summary by Albuisson et al., 2013).
Dehydrated red blood cells, including those from hereditary xerocytosis patients, show delayed infection rates to Plasmodium in vitro, suggesting a potential protective mechanism against malaria (Tiffert et al., 2005). A polymorphism in PIEZO1 that is enriched in populations of African descent and results in xerocytosis conferred resistance to Plasmodium infection in vitro (see 611184.0016).
The 'leaky red blood cells' in familial pseudohyperkalemia show a temperature-dependent loss of potassium when stored at room temperature, manifesting as apparent hyperkalemia. The red blood cells show a reduced life span in vivo, but there is no frank hemolysis. Studies of cation content and transport show a marginal increase in permeability at 37 degrees C and a degree of cellular dehydration, qualitatively
similar to the changes seen in dehydrated hereditary stomatocytosis. Physiologic studies show that the passive leak of potassium has an abnormal temperature dependence, such that the leak is less sensitive to temperature than that in normal cells (summary by Iolascon et al., 1999).
Carella et al. (2004) noted that 3 clinical forms of pseudohyperkalemia unassociated with hematologic manifestations, based predominantly on the leak-temperature dependence curve, had been reported: (1) pseudohyperkalemia Edinburgh, in which the curve has a shallow slope; (2) pseudohyperkalemia Chiswick or Falkirk (see 609153), in which the curve is shouldered; and (3) pseudohyperkalemia Cardiff (see 609153), in which the temperature dependence of the leak shows a 'U-shaped' profile with a minimum at 23 degrees C. Gore et al. (2004) stated that potassium-flux temperature profiles are consistent both from year to year in an individual as well as consistent within affected members of a pedigree.
Genetic Heterogeneity of Hereditary Stomatocytosis
Dehydrated hereditary stomatocytosis-2 (DHS2; 616689) is caused by mutation in the KCNN4 gene (602754) on chromosome 19q13. Another form of stomatocytosis, involving familial pseudohyperkalemia with minimal hematologic abnormalities (PSHK2; 609153), is caused by mutation in the ABCB6 gene (605452) on chromosome 2q35. Cryohydrocytosis (CHC; 185020) is caused by mutation in the SLC4A1 gene (109270) on chromosome 17q21, and stomatin-deficient cryohydrocytosis with neurologic defects (SDCHCN; 608885) is caused by mutation in the SLC2A1 gene (138140) on chromosome 1p34. An overhydrated form of hereditary stomatocytosis (OHST; 185000) is caused by mutation in the RHAG gene (180297) on chromosome 6p12.
Reviews
Delaunay (2004) reviewed genetic disorders of red cell membrane permeability to monovalent cations, noting 'inevitable' overlap between entities based on clinical phenotype.
Bruce (2009) provided a review of hereditary stomatocytosis and cation-leaky red cells, stating that consistent features include hemolytic anemia, a monovalent cation leak, and changes in red cell morphology that appear to follow a continuum, from normal discocyte to stomatocyte to echinocyte in DHS, and from discocyte to stomatocyte to spherocyte to fragmentation in OHST. Bruce (2009) suggested that the underlying pathologic mechanism might involve misfolded mutant proteins that escape the quality control system of the cell and reach the red cell membrane, where they disrupt the red cell membrane structure and cause a cation leak that alters the hydration of the red cell, thereby changing the morphology and viability of the cell.
King and Zanella (2013) provided an overview of 2 groups of nonimmune hereditary red cell membrane disorders caused by defects in membrane proteins located in distinct layers of the red cell membrane: red cell cytoskeleton disorders, including hereditary spherocytosis (see 182900), hereditary elliptocytosis (see 611804), and hereditary pyropoikilocytosis (266140); and cation permeability disorders of the red cell membrane, or hereditary stomatocytoses, including DHS, OHST, CHC, and PSHK. The authors noted that because there is no specific screening test for the hereditary stomatocytoses, a preliminary diagnosis is based on the presence of a compensated hemolytic anemia, macrocytosis, and a temperature- or time-dependent pseudohyperkalemia in some patients. King et al. (2015) reported the International Council for Standardization in Haematology (ICSH) guidelines for laboratory diagnosis of nonimmune hereditary red cell membrane disorders. [from
OMIM]