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 K levels of 41-48 and 44-53 mmol/(l cells) respectively. This anaemia was associated with marked 'pseudohyperkalaemia': that is, loss of K from red cells on storage at room temperature. At 37°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°C (mean Q10 (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°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.