Hypokalemia of renal origin can arise from genetic abnormalities in a variety of transporters or channel
proteins that mediate tubular handling of
potassium. Recently, mutations in
claudin 10 have been documented in patients with
hypokalemia in association with a range of other
electrolyte abnormalities and skin and sweat gland manifestations. We report a 12-year-old Hispanic boy who presented with anhydrosis, aptyalism,
alacrima,
hypokalemia, and hypocalciuria, in whom we detected a homozygous mutation in the
claudin 10 gene. During the 4-year follow-up period, he developed hypermagnesemia and a decline in estimated glomerular filtration rate to 59mL/min/1.73m2. His unaffected parents and siblings were heterozygous for the mutation. We summarize the clinical phenotype encountered in patients with
claudin 10 mutations. It is characterized by significant heterogeneity in
electrolyte and extrarenal abnormalities and is associated with a risk for progressive loss of kidney function in up to 33% of cases. Awareness of this association between
claudin 10 mutations and
electrolyte abnormalities, namely
hypokalemia and hypermagnesemia, sheds new light on the physiology of
potassium and
magnesium handling along the nephron and increases the likelihood of identifying the underlying tubular mechanism in patients with newly diagnosed
hypokalemia with or without concomitant hypermagnesemia.