Functional effects of genetic variants in the 11beta-hydroxylase (CYP11B1) gene.

Abstract

OBJECTIVE:

We previously described an association between the -344C/T 5'-untranslated region (UTR) polymorphism in the CYP11B2 (aldosterone synthase) gene and hypertension with a raised aldosterone to renin ratio (ARR); the same genetic variant is also associated with impaired adrenal 11beta-hydroxylase efficiency. The -344 polymorphism does not seem to be functional, so is likely to be in linkage with variants in CYP11B1 that determine the associated variation in 11beta-hydroxylase efficiency. We therefore aimed to determine whether there is an association between CYP11B1 variants and hypertension and/or an altered ARR.

DESIGN AND MEASUREMENTS:

We screened 160 subjects divided into four groups, normotensive controls, unselected hypertensive subjects, and hypertensive subjects with either a high (> or = 750) or low ARR (< or = 200), for variants in the coding region of CYP11B1 by single-stranded conformation polymorphism (SSCP) and direct sequencing. The effects of these variants on enzyme function were assessed by conversion of 11-deoxycortisol to cortisol and 11-deoxycorticosterone (DOC) to corticosterone.

RESULTS:

Eight novel missense mutations were identified in the CYP11B1 gene that alter the encoded amino acids: R43Q, L83S, H125R, P135S, F139L, L158P, L186V and T196A. In each case they were heterozygous changes. However, no mutations were identified that could account for hypertension and/or a raised ARR. The variants L158P and L83S severely impaired enzyme function while R43Q, F139L, P135S and T196A enzymes resulted in product levels that were approximately 30-50% that of wild-type levels. The variant enzymes H125R and L186V resulted in substrate-specific alterations in enzyme function. H125R decreased conversion of 11-deoxycortisol to cortisol and L186V increased 11-deoxycortisol conversion. Neither had an effect on the conversion of DOC to corticosterone.

CONCLUSION:

No variants were identified in the coding region of CYP11B1 that could account for hypertension and/or a raised ARR. However, this in vitro study identifies the importance of these affected residues to enzyme function and will inform subsequent studies of structure-function relationships.

• Authors: Marianne Barr, Scott M MacKenzie, Donna M Wilkinson, Christine D Holloway, Elaine C Friel, Stephen Miller, Tom MacDonald, Robert Fraser, John M C Connell, Eleanor Davies
• Journal: Clinical endocrinology (Clin Endocrinol (Oxf)) Vol. 65 Issue 6 Pg. 816-25 (Dec 2006) ISSN: 0300-0664 [Print] England
• PMID: 17121536 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Desoxycorticosterone
• Aldosterone
• Steroid 11-beta-Hydroxylase
• Renin
• Corticosterone
• Cortodoxone
• Hydrocortisone

Topics

• Adolescent
• Adult
• Aged
• Aged, 80 and over
• Aldosterone (metabolism)
• Animals
• Biological Assay (methods)
• Case-Control Studies
• Corticosterone (metabolism)
• Cortodoxone (metabolism)
• Desoxycorticosterone (metabolism)
• Humans
• Hydrocortisone (metabolism)
• Hyperaldosteronism (complications, genetics, metabolism)
• Hypertension (complications, genetics, metabolism)
• Middle Aged
• Mutation, Missense
• Polymorphism, Single Nucleotide
• Rats
• Renin (metabolism)
• Sequence Analysis, DNA
• Steroid 11-beta-Hydroxylase (genetics, metabolism)