Hypercalciuria in familial hyperkalemia and hypertension accompanies hyperkalemia and precedes hypertension: Description of a large family with the Q565E WNK4 mutation

Familial hyperkalemia and hypertension (FHH; pseudohypoaldosteronism type II) is an autosomal dominant disorder characterized by hyperkalemia, hypertension, and low renin. WNK1 kinase overexpression and WNK4 kinase inactivating missense mutations cause FHH. When expressed in frog oocyte, WNK4 inhibits Na-Cl cotransporter surface expression, and WNK1 relieves this inhibition. We have reported hypercalciuria in subjects with the WNK4 Q565E mutation. In contrast, in subjects with WNK1 overexpression, normocalciuria was found. Here we report a major extension of our previously described kindred that contains 34 subjects, 18 of them affected by the mutation. Hypertension was diagnosed in 13 affected subjects at the age of 31 ± 12 yr. Five of the affected or obligatory affected subjects had stroke, in four at the age of 50-62 yr. Seven subjects with FHH were diagnosed 27 yr previously. All four subjects who were normotensive at diagnosis became hypertensive during follow-up. The mean time between detection of hyperkalemia and appearance of hypertension was 13 yr. In the extended kindred, compared with the unaffected subjects, affected subjects had hyperkalemia, low transtubular potassium gradient, hyperchloremia, low bicarbonate, higher aldosterone, and marked suppression of renin. Urinary calcium levels in affected and unaffected subjects were 0.85 ± 0.27 and 0.28 ± 0.12 mmol/mmol creatinine, respectively (P < 0.0001). Hypercalciuria was accompanied by lower serum calcium levels [9.44 ± 0.15 vs. 9.81 ± 0.31 mg/dl (2.36 ± 0.04 vs. 2.45 ± 0.08 mmol/liter); P = 0.01], supporting a mechanism of renal calcium leak. The six affected, currently normotensive subjects had the same degree of hyperkalemia, hypercalciuria, and low renin as the affected hypertensive subjects. We conclude that in FHH with WNK4 mutations, with time all affected subjects will apparently develop hypertension. Hypercalciuria accompanies hyperkalemia, and both precede hypertension. Based on the recent findings that WNK4 regulates the renal outer medullary potassium channel as well as epithelial Cl ^-/base exchanger and the Na⁺-K⁺-2Cl^- cotransporter, we suggest that WNK4 interacts with a calcium channel or transporter.