Apparent Mineralocorticoid Excess (AME) is a rare autosomal recessive syndrome characterized by plasma volume expansion, hypertension, hypokalemic acidosis, and a suppressed rennin-angiotensin-aldosterone system. Cortisol to cortisone conversion is impaired in patients, due to defects in the 11-Beta-Hydroxysteroid Dehydrogenase, Type II (HSD11B2) enzyme. Severe deficiency of this enzyme results in markedly elevated urinary ratio of cortisol (F), tetrahydrocortisone-F (THF), and allo-THF to cortisone (E), tetrahydrocortisone (THE), and allo-THE. Typical symptoms of the condition in children include low birth weight, failure to thrive, short stature, severe hypertension, hypokalemic metabolic acidosis, muscle weakness, delayed puberty, frequent urination and thirst, renal insufficiency, and hypokalemic nephropathy, resulting in nephrocalcinosis or polycystic kidneys. A milder version of the condition is also seen in some patients, in whom the disease manifests only in adulthood, and is characterized by a decreased rate of cortisol clearance and turnover but a normal urinary ratio of THF to THE. In such patients, some residual enzyme activity may be responsible for the milder phenotype. AME is extremely rare, with only fewer than 100 cases having been reported in medical literature.
Generally, the THF+allo-THF/THE ratio is used to diagnose AME in patients with mineralocorticoid excess. AME is associated with mutations in HSD11B2 gene. Therefore, molecular analysis of the HSD11B2 gene can be employed to confirm or diagnose the condition in patients. Treatment, however, is difficult. Sort-term treatment may involve a low-sodium diet and administering spironolactone. Dexamethasone is a more effective alternative; yet, it has growth suppressing effects, and therefore, is not suitable for children over a long period of time. Prognosis in some patients may not be good despite medications, and death within a few years of being diagnosed with AME is not uncommon.