Hereditary stomatocytosis

Hereditary stomatocytosis is the name for a number of inherited conditions, mostly autosomal dominant, that affect the red blood cell. On a peripheral blood smear the affected cells show a slit-like area of central pallor, the stomatocyte. Their membranes can abnormally leak sodium or potassium ions, which upsets cell volume. Two varieties are separated by hydration: overhydrated forms, linked to genes for the band three complex such as RHAG, and dehydrated forms, called hereditary xerocytosis, caused by mutations in PIEZO1 or more rarely KCNN4. The red cells are fragile and are destroyed early, so people may show fatigue, pallor, jaundice, an enlarged spleen and gallstones from long-running hemolysis. Hereditary stomatocytosis has to be distinguished from acquired causes of stomatocytosis, such as phenytoin toxicity and alcoholism, and from misleading appearances created while the smear is prepared.