Familial hypokalemia associated with renal interstitial fibrosis

Two brothers with persistent hypokalemia and elevated plasma renin levels were evaluated. No other consistent abnormalities of their blood chemistries or renal function were noted. The elder brother had symptomatic fatigue and muscle cramps, and complained of nausea and intermittent vomiting. He was also unable to conserve sodium when adhering to a low sodium diet. On a high sodium diet and triamterene, his potassium level returned to normal. Aldosterone levels were slightly elevated. On kidney biopsy, there was focal interstitial fibrosis and proximal tubular degeneration, but the juxtaglomerular apparatus appeared normal. The younger brother was asymptomatic and was able to retain sodium when placed on a sodium-restricted diet. A review of familial and nonfamilial causes of hypokalemia did not reveal a similar disease state. Three additional family members also had elevated plasma renin levels and/or decreased plasma potassium levels. It is possible that these brothers and their siblings represent a previously undescribed form of familial hypokalemia. The Inability to retain sodium while on a restricted diet with a normal glomerular filtration rate and elevated aldosterone levels suggests a possible defect in the proximal tubules as the fundamental abnormality in these patients.