PURPOSE: Renal pseudohypoaldosteronism type 1 (PHA1) is a rare disease affecting infants. Symptoms are failure to thrive, vomiting, and weight loss. It is caused by gene variants in NR3C2 by which the mineralocorticoid receptor is dysfunctional, and patients develop hyponatremia, elevated plasma aldosterone, and renin but have normal blood pressure. Little is known about PHA1 in adults. We present four adults with PHA1, their clinical, biochemistry, and genetic data. METHODS: Clinical and biochemical data were collected from the medical files and clinical examination of the participants. Genetic testing was performed. RESULTS: Two adult dizygotic twins and their mother, as well as an adult man were included. One of the sisters and the man had had severe hyponatremia and been admitted several times as young infants, treated with sodium chloride and fludrocortisone. All had as adults elevated plasma aldosterone and normal sodium. The females now had normal plasma renin, but it was increased in the male. A novel genetic variant in NR3C2 was found in the twins and their mother (c.1816T>
C, p.(Cys606Arg)). All had normal blood pressure and were asymptomatic. CONCLUSION: In adulthood, PHA1 seems to be asymptomatic and long-term consequences favorable.