A variant of hereditary stomatocytosis with marked pseudohyperkalaemia

A family with an unusual form of hereditary stomatocytosis is described. Th e affected members showed a mild, dominantly-inherited, haemolytic anaemia with intracellular Na and It levels of 41-48 and 44-53 mmol/(I cells) respe ctively. This anaemia was associated with marked 'pseudohyperkalaemia': tha t is, loss of It from red cells on storage at room temperature. At 37 degre es C, 'leak' tracer flux rates (assessed as the ouabain + bumetanide-resist ant K fluxes) showed a roughly 5-fold acceleration compared to normal, and an abnormal temperature dependence with a shallow slope between 37 and 20 d egrees 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 attr ibuted to the disparity between pump and leak at 20 degrees C. This is an i dentical mechanism to that previously shown for the haematologically trivia l condition, 'familial pseudohyperkalaemia'. No protein or lipid abnormalit y was found in the membrane of these cells.