Background: Apparent mineralocorticoid excess (AME) is a cause of low-renin, low-aldosterone hypertension in which cortisol acts as a mineralocorticoid. The condition reflects an inability to inactivate cortisol to cortisone due to defective activity of the type 2 isozyme of 11b-hydroxysteroid dehydrogenase (11β-HSD2). Homozygous mutations in 11b-HSD2 gene in patients with AME have been described. A 7-year-old Brazilian girl had previously been found to have AME. Her father recently presented with mineralocorticoid hypertension at age 38 years.
Objective: To describe the clinical details, to perform steroid analyses and to assess the molecular basis for the hypertension in this kindred.
Methods: The 11βHSD2 gene was amplified from genomic DNA by the polymerase chain reaction and sequenced by direct chain-termination sequencing on an automatic DNA sequencer. The sequencing results were validated by restriction-site polymorphism. The mutant 11β-HSD2 protein was expressed in Chinese hamster ovary polyoma cells and enzymatic activity was assessed by metabolizing cortisol in vitro.
Results: Sequence analysis of genomic DNA revealed a novel C1061T point mutation in exon V of the human 11β-HSD2 gene, resulting in an amino acid substitution of alanine by valine at codon 328 of the enzyme protein (A328V). Expression studies confirmed that the mutant protein was devoid of 11β-HSD2 activity. A HhaI restriction-site polymorphism confirmed that the proband was homozygous for the mutation whereas both parents were heterozygotes. The father of the proband had hypertension, a normal serum potassium level, suppressed plasma renin activity and plasma aldosterone level and a moderately elevated urinary cortisol: cortisone metabolite ratio.
Conclusions: AME in this kindred is caused by a novel mutation in the 11β-HSD2 gene. Detection of hypokalaemia, at least in this kindred, is an insensitive screening test for mineralocorticoid-based hypertension. In contrast to results from previously investigated kindreds, we have demonstrated that this kindred has an abnormal phenotype in the heterozygote state. Further studies are now required in order to evaluate the role of 11β-HSD2 activity in the pathophysiology of 'essential' hypertension.