Novel mutation in the epithelial sodium channel causing type I pseudohypoaldosteronism in a patient misdiagnosed with cystic fibrosis.

UNLABELLED: Cystic fibrosis (CF) is an inherited disorder with a devastating prognosis. Determination of chloride concentration in sweat has been the gold standard test for diagnosing CF for over 50 years and still remains the primary screening test. However, now that the genetic cause is known and can be studied, genetic confirmation is mandatory in every suspected patient. We present a patient who had been clinically diagnosed and whose genetic testing could not confirm CF, leading us to search for other options that may also give a positive sweat test. The patient turned out to suffer type 1 pseudohypoaldosteronism, a condition that may cause severe dehydration, hyponatremia and hyperkalemia episodes if not diagnosed and treated early with sodium supplementation. We found a genetic variation in the epithelial sodium channel gene which has not been reported previously, and we discuss the possibility of it being the cause of our patient's phenotype.
CONCLUSION: this patient clearly illustrates the usefulness of genetic confirmation for CF for the diagnosis and genetic counselling, even when it is clinically oriented, and describes a novel mutation of the amiloride-sensitive epithelial sodium channel possibly causing type 1 pseudohypoaldosteronism.