A RARE CASE OF GENE CYP11B1 DEFICIENCY CAUSING HYPERALDOSTERONISM

M KAYES1, S TARAFDAR1, 2

1Department of Renal Medicine, Blacktown Hospital, Sydney, New South Wales; 2Western Sydney University, Sydney, New South Wales

Background: Defect in the gene CYP11B1 and the subsequent deficiency in the enzyme 11-beta-hydroxylase 1(11β-OH1) is a rare cause of congenital adrenal hyperplasia (CAH). 11β-OH1 plays a major role in cortisol synthesis by converting 11-deoxycortisol to cortisol. It also has a supportive role for 11β-OH2 in aldosterone synthesis by converting 11-deoxycorticosterone to corticosterone.

Clinical features of 11β-OH1 deficiency include ambiguous genitalia, accelerated skeletal maturation, short stature, precocious puberty due to androgen excess and hypokalaemic hypertension from excess 11-deoxycorticosterone.

Case Report: A 27 year old male presented with hypertensive urgency, hypokalaemia and metabolic alkalosis on a background of hypertension from age 21. Known to be noncompliant with treatment, investigations revealed a plasma aldosterone level of 547pmol/L with plasma renin concentration of <2.2mIU/L indicating an aldosterone to renin ratio of more than 200 (normal <30).  CT imaging of the adrenal glands were unremarkable. Given his young age and strong family history of early onset hypertension, patient had genetic testing revealing a large deletion in CYP11B1. There was no evidence of hyperandrogenism.

Conclusions: 11β-OH1 associated CAH is characterised by hyperandrogenism with accumulation of 11-deoxycortisol and 11-deoxycorticosterone. 11-deoxycorticosterone (which has intrinsic mineralocorticoid activity) causes hypokalaemic hypertension and supressed aldosterone production. However, our patient had a significantly elevated aldosterone to renin ratio suggesting that blockage of the cortisol pathway caused activation of the mineralocorticoid pathway instead of the androgen pathway.

This is the first documented case of a deletion in gene CYP11B1 presenting with both hypertension and hyperaldosteronism instead of hypertension, hyperandrogenism and hypoaldosteronism. This case suggests that depending on which pathway is predominantly activated (aldosterone or androgens), deletion of CYP11B1 can lead to either CAH or a novel hyperaldosteronism.

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