Aldosterone, the most important mineralocorticoid, regulates electrolyte excretion and intravascular volume mainly through its effects on renal distal convoluted tubules and cortical collecting ducts. Excess secretion of aldosterone or other mineralocorticoids or abnormal sensitivity to mineralocorticoids may result in hypertension, suppressed plasma renin activity, and hypokalemia. Such conditions often have a genetic basis, and studies of these conditions have provided valuable insights into the normal and abnormal physiology of mineralocorticoid action. Deficiencies of steroid 11 beta-hydroxylase or 17 alpha-hydroxylase are types of congenital adrenal hyperplasia, the autosomal recessive inability to synthesize cortisol. These two defects often cause hypertension because of overproduction of cortisol precursors that are, or are metabolized to, mineralocorticoid agonists. These disorders result from mutations in the CYP11B1 and CYP17 genes encoding the corresponding enzymes. Glucocorticoid-suppressible hyperaldosteronism is an autosomal dominant form of hypertension in which aldosterone secretion is abnormally regulated by corticotropin. It is caused by recombinations between linked genes encoding closely related isozymes, 11 beta-hydroxylase (CYP11B1) and aldosterone synthase (CYP11B2), generating a dysregulated chimeric gene with aldosterone synthase activity. Apparent mineralocorticoid excess is a loss of functional ligand specificity of the mineralocorticoid receptor caused by a deficiency of the kidney isozyme of 11 beta-hydroxysteroid dehydrogenase, an enzyme that normally metabolizes cortisol to cortisone to prevent cortisol from occupying the receptor. This autosomal recessive form of severe hypertension results from mutations in the HSD11K (HSD11B2) gene.