Endocrine Abstracts

Isolated hyperreninemic hypoaldosteronism presents in infancy with failure to thrive, hyponatremia, hyperkalemia, markedly elevated plasma renin activity, and low or inappropriately normal aldosterone. It is usually caused by mutations in the CYP11B2 gene encoding aldosterone synthase. Patients have normal cortisol levels and no features of congenital adrenal hyperplasia. We report a patient who presented with hyperreninemic hypoaldosteronism in early infancy.

Case Report: A 38 years old presented on the 18th day of her birth with hyponatremia, hyperkalemia, dehydration and failure to thrive. Chromosomal analysis confirmed a normal female karyotype of 46, XX. She had normal cortisol and 17-hydroxyprogesterone levels by cosyntropin stimulation testing and normal ACTH levels. She had high plasma renin activity, low aldosterone level, and elevated 18-hydroxycorticosterone, compatible with type 2 aldosterone synthase deficiency. The patient was heterozygous for a novel CYP11B2 mutation: c. 1157C > A (p.Val 386Ala). She was treated with fludrocortisone and has been symptomatic. She delivered a healthy baby girl last year.

Discussion: Salt-wasting forms of congenital adrenal hyperplasia are relatively common causes of hyperreninemic hypoaldosteronism. Aldosterone regulates electrolytes and deficiency results in hyponatremia, hypovolemia, and hyperkalemia. Plasma renin activity (PRA) is elevated. Aldosterone synthase is a mitochondrial cytochrome P450 enzyme, CYP11B2. It is encoded by the CYP11B2 gene located on chromosome 8. Most patients with aldosterone synthase deficiency carry inactivating mutations in CYP11B2 gene. It is an autosomal recessive disorder, presenting with severe salt-losing in early infancy usually at the age of 1–2 months with diarrhea, failure to thrive, severe dehydration and no virilisation. Plasma electrolytes show. Patients have hyponatremia, hyperkalemia, and acidosis with normal cortisol response and elevated plasma renin activity with low aldosterone levels. All respond to fludrocortisone treatment. Our case illustrates the clinical significance to recognize this condition as it has a good long-term prognosis when adequate fludrocortisone replacement is instituted.