A variant of hereditary stomatocytosis with marked pseudohyperkalaemia

A family with an unusual form of hereditary stomatocytosis is described. The affected members showed a mild, dominantly-inherited, haemolytic anaemia with intracellular Na and It levels of 41-48 and 44-53 mmol/(I cells) respectively. This anaemia was associated with marked 'pseudohyperkalaemia': that is, loss of It from red cells on storage at room temperature. At 37 degrees C, 'leak' tracer flux rates (assessed as the ouabain + bumetanide-resistant K fluxes) showed a roughly 5-fold acceleration compared to normal, and an abnormal temperature dependence with a shallow slope between 37 and 20 degrees C (mean Q(10) (ratio of reaction rates at temperature T and T - 10) over this interval, 1.6; normal 2.2). The pseudohyperkalaemia could be attributed to the disparity between pump and leak at 20 degrees C. This is an identical mechanism to that previously shown for the haematologically trivial condition, 'familial pseudohyperkalaemia'. No protein or lipid abnormality was found in the membrane of these cells.