Mutations in CYP11B1 gene converting 11 beta-hydroxylase into an aldosterone-producing enzyme are not present in aldosterone-producing adenomas

In the human adrenal cortex, cortisol and aldosterone are synthesized by th e isozymes 11 beta-hydroxylase and aldosterone synthase, respectively, enco ded by the 93% identical CYP11B1 and CYP11B2 genes. In vitro mutagenesis of CYP11B1 complementary DNA, resulting in the replacement of CYP11B1 codons by those encoding the corresponding amino acid residues of CYP11B2 enzyme ( exon 5, Ser(288)Gly; exon 6, Val(320)Ala), yields a complementary DNA encod ing a mutant enzyme with an efficient aldosterone synthase activity. Identi cal somatic mutations in the CYP11B1 gene in vivo would produce a gene enco ding an enzyme with C-18 activity and that would preserve ACTH responsivene ss due to the retained 5'-promoter in the mutated CYP11B1 gene. An ACTH-res ponsive aldosterone synthase activity of this type is commonly seen in pati ents with aldosterone-producing adenomas (APA). We examined the occurrence of mutations in exons 5 and 6 of the CYP11B1 gene in APA from 10 patients w ith primary aldosteronism. Patients were selected on preoperative evidence of a 50% or greater plasma aldosterone decrease after short term dexamethas one trial and no aldosterone response to upright posture. DNA from adenomas was amplified by PCR using two pairs of primers spanning the regions of CY P11B1 gene, i.e. exons 3-5 and exons 6-9, where mutations could be located. Targeted regions were screened for mutations by automated sequencing of PC R products. No point mutations of the CYP11B1 gene over the two regions exa mined were found in APA. This argues against involvement of mutations in th e pathogenesis of ACTH-responsive APA.