Familial pseudohyperkalaemia Cardiff: a mild version of cryohydrocytosis.

We have investigated a Welsh pedigree showing the 'familial pseudohyperkalaemia' phenotype of dominantly inherited, red-cell-based, temperature-dependent pseudohyperkalaemia associated with normal haematology. The 'passive leak' to K across the membrane of these abnormal red cells showed a 'U-shaped' temperature dependence, with a minimum at about 23 degrees C, qualitatively similar to that seen in the frankly haemolytic 'cryohydrocytosis' variant of the hereditary stomatocytosis group. Like three previous pedigrees with cryohydrocytosis, these patients show an excess of ether lipids in the membrane. However, these patients differ from other 'familial pseudohyperkalaemia' pedigrees, in which the leak showed different temperature profiles.