Asymptomatic chronic hypomagnesemia and hypokalemia in a child: Cell membrane disease.

An 8-year-old boy was followed for four years because of chronic hypomagnesemia and hypokalemia. THe clinical manifestations were episodic and characterized by spontaneous carpopedal spasm. There were no other signs of magnesium or potassium deficiency. Metabolic studies revealed that the urinary exceretion of magnesium and potassium was elevated in relation to the serum level, but appropriate for a normal boy of that age. No abnormality was detected in the renin-angiotensin-aldosterone system, and the renal functions were normal. Various therapeutic attempts (oral magnesium and/or potassium supplements, spironolactone) failed to correct the abnormal serum concentrations of magnesium and potassium. This disease may represent a defect in the maintenance of a normal gradient between intra-and extracellular magnesium and potassium.