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


METHODS
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.


CONCLUSIONS
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.
Barr
Marianne
M
Division of Cardiovascular and Medical Sciences, BHF Glasgow Cardiovascular Research Centre, University of Glasgow, Glasgow, UK.
MacKenzie
Scott M
SM
Wilkinson
Donna M
DM
Holloway
Christine D
CD
Friel
Elaine C
EC
Miller
Stephen
S
MacDonald
Tom
T
Fraser
Robert
R
Connell
John M C
JM
Davies
Eleanor
E
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000450:Aldosterone / Q000378:metabolism; D000818:Animals; D001681:Biological Assay / Q000379:methods; D016022:Case-Control Studies; D003345:Corticosterone / Q000378:metabolism; D003350:Cortodoxone / Q000378:metabolism; D003900:Desoxycorticosterone / Q000378:metabolism; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism; D006929:Hyperaldosteronism / Q000150:complications / Q000235:genetics / Q000378:metabolism*; D006973:Hypertension / Q000150:complications / Q000235:genetics / Q000378:metabolism*; D008875:Middle Aged; D020125:Mutation, Missense; D020641:Polymorphism, Single Nucleotide; D051381:Rats; D012083:Renin / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013252:Steroid 11-beta-Hydroxylase / Q000235:genetics* / Q000378:metabolism*
D003900:Desoxycorticosterone; D000450:Aldosterone; D013252:Steroid 11-beta-Hydroxylase; D012083:Renin; D003345:Corticosterone; D003350:Cortodoxone; D006854:Hydrocortisone