What is the Origin of Apparent Mineralocorticoid Excess?

The name "Apparent Mineralocorticoid Excess" was coined because the patient presents with all the classic symptoms of mineralocorticoid overactivity, yet the primary hormone, aldosterone, is not actually elevated. The syndrome was first described clinically, and the underlying enzymatic defect was later identified, leading to the term apparent to denote the functional excess without a true hormonal overproduction. This nomenclature precisely reflects the clinical presentation juxtaposed with the distinct biochemical findings.

What is the Mechanism of Apparent Mineralocorticoid Excess?

The underlying cause is typically a genetic defect or inhibition of the enzyme 11-beta hydroxysteroid dehydrogenase type 2 (11β-HSD2), which is predominantly found in the renal tubules. This enzyme normally inactivates the potent glucocorticoid cortisol into the inactive cortisone. When 11β-HSD2 function is impaired, high local concentrations of cortisol inappropriately bind and activate the mineralocorticoid receptor (MR) with high affinity. This pathological MR activation leads to increased epithelial sodium channel activity, causing excessive sodium reabsorption and potassium excretion, which produces the clinical syndrome.

Apparent Mineralocorticoid Excess

Meaning

Apparent Mineralocorticoid Excess (AME) is a rare, inherited endocrine disorder characterized by the clinical triad of hypertension, hypokalemia, and metabolic alkalosis, which functionally mimics an excess of the mineralocorticoid hormone aldosterone. Crucially, laboratory testing reveals suppressed plasma renin activity and very low aldosterone levels, distinguishing it definitively from primary aldosteronism. This condition highlights a fundamental, non-aldosterone-driven issue in the body’s salt and water balance regulation, significantly impacting cardiovascular and renal health.