The Syndrome of Apparent Mineralocorticoid Excess

This chapter provides information on clinical features of the syndrome of apparent mineralocorticoid excess (AME) and explains the molecular genetic analysis of apparent mineralocorticoid excess (AME). The clinical features seen in patients with AME include moderate intrauterine growth retardation and postnatal failure to thrive. Hypokalemia is often more severe than that seen in primary aldosteronism, with consequences including nephrocalcinosis and nephrogenic diabetes insipidus and the latter condition causes polyuria and polydipsia. Hypokalemia also has deleterious effects on muscles ranging from elevations in serum creatine phosphokinase to frank rhabdomyolysis. Patients with AME have abnormal cortisol metabolism. Plasma cortisol half-life is prolonged from the normal of approximately 80 minutes to 120-190 minutes. This is due to a marked deficiency in 11β-dehydrogenation. A low salt diet, potassium supplementation, and spironolactone are the most often used therapies for AME. Triamterine and amiloride, other potassium-sparing diuretics, have also been successfully used, particularly because it is difficult to distinguish AME from Liddle's syndrome without specialized steroid assays. These two agents block the epithelial sodium channel. The hypertension of AME has also been treated with nifedipine. Although ACTH exacerbates the signs of this disorder, suppressing ACTH secretion with dexamethasone has been effective in ameliorating hypokalemia and hypertension only in mild cases. The hypertension in AME is salt-sensitive, so it is reasonable to speculate that reduced activity of 11-HSD2 from whatever cause could increase the sensitivity of blood pressure to salt loading in otherwise normal individuals and/or be a risk factor for developing hypertension. © 2009