Unusual low plasma renin hypertension in a child

A four-year-old girl with hypertension (140/60) and chronic hypokalemic alkalosis was studied to determine the origin of this clinical feature. High exchangeable sodium (56.7 meq/kg vs. 45-55 meq/kg in controls) was associated with a low plasma renin activity (6 ng/1/min vs. 26 +/- 3.1 in controls) and reduced aldosterone secretion rate (5.56 mug/day; normal: 50-150 mug per day)). A low corticosterone secretion rate (0.228 mg/day vs. 0.50-0.65 in controls) and urinary tetrahydrodeoxycorticosterone (0.007 mg/day vs. 0.03-0.09 mg/day in controls) were found. The basal secretion rate of cortisol was also low (1.80 mg/m2/day vs. 5.4-16.7 mg/m2/day in controls) in spite of normal plasma ACTH: 78 pg/ml. The normal increase of the cortisol secretion rate (from 1.80 to 65 mg/m2/day) after synthetic ACTH stimulation ruled out a 17 alpha hydroxylase deficiency. The low sweat Na/K ratio (0.25) and the good suppressing efficacy of dexamethasone and of the spironolactones on hypertension and on the hypokalemic alkalosis agreed with the hypersecretion of a mineralocorticoid. The secretion rate of 18 hydroxydeoxycorticosterone was high (91 mug/day/1.73 m2 vs. 40-80 mug per day and per 1.73 m2). As the mineralocorticoid potency of this steroid is weak, we speculate that it might be the precursor of a more potent but unknown mineralocorticoid which could influence the ACTH secretion.