Definition:

Overhydrated hereditary stomatocytosis (OHST), which is clinically characterized by a hemolytic anemia, is a rare, dominantly inherited disorder of red blood cells (RBCs) associated with increased membrane permeability to monovalent cations and increased activity of the Na+K+-ATPase. The influx of Na+ exceeds the loss of K+ causing water influx and resulting in swollen erythrocytes, hemolysis, and stomatocyte formation. The OHST phenotype is also associated with a dramatic decrease or the absence of the 32-kDa membrane raft protein stomatin. OHST diagnosis is based on a hemolytic anemia associated with a massive right shift of the osmotic gradient ektacytometry curve and a decreased osmotic resistance, together with a major increase in a monovalent cation leak. Recently, OHST was found to be linked to amino acid substitutions in Rh-associated glycoprotein (RhAG).