CYP11B2-CYP11B1 haplotypes associated with decreased 11 beta-hydroxylase activity.

Reduced adrenal 11 beta-hydroxylation has been associated with an aldosterone synthase (CYP11B2) polymorphism. The 11 beta-hydroxylase gene (CYP11B1) lies close to CYP11B2. We hypothesize that a molecular variant in CYP11B2 is in linkage disequilibrium (LD) with a key quantitative trait in CYP11B1 determining this phenotype. Polymorphisms and inferred haplotypes at CYP11B loci were studied in two independent populations from Europe (n = 100) and South America (n = 99). The latter underwent detailed hormonal studies. LD was estimated by alternative Bayesian methods for inferring the extent of LD when haplotypes at different loci are inferred. Population differences in single nucleotide polymorphisms were modest, indicating the stability of both genes across populations. Using five of nine potentially informative loci at CYP11B sites with allele frequency greater than 0.1, two major contrasting haplotypes, CwtCG and TconvGTA, were found. In both populations the CwtCG haplotype accounted for 44% and the TconvGTA for 32% of subjects. Haplotype distribution did not differ between Europeans and South Americans (chi(2) = 2.81; P = 0.09). In vivo 11 beta-hydroxylase activity, estimated from urinary steroid profiling, was lower in subjects with an increased aldosterone to renin ratio or with the TconvGTA haplotype. These findings indicate that genotypes at the CYP11B locus are in strong LD and that identified haplotypes predict 11 beta-hydroxylase activity.

Low prevalence of nonconservative mutations of serum and glucocorticoid-regulated kinase (SGK1) gene in hypertensive and renal patients.

BACKGROUND: The serum- and glucocorticoid-regulated kinase (SGK1) gene is an important mediator of aldosterone action, regulating the expression of the renal epithelial Na(+) channel. In renal failure, blood pressure (BP) is markedly salt-dependent and increases with decreasing renal function. Mutations of the SGK1 gene affecting phosphorylation could be responsible for salt-mediated increases in BP and hypertension-related progression to end-stage renal disease (ESRD). METHODS: The SGK1 gene was analysed for mutations in the exons 4, 5, 8 and 10-12, because of potential phosphorylation sites, in 591 subjects, including 311 ESRD patients (either dialysis or transplanted). In addition, an intron 6 single-nucleotide polymorphism (SNP) described previously was also investigated in this study. Genotyping was performed either by using a strategy based on single strand conformation polymorphism analysis of polymerase chain reaction (PCR) products and subsequent direct sequencing of identified gel shift variants or by using high throughput 5' nuclease allelic discrimination assay. RESULTS: Two SNPs in coding regions of SGK1 potentially influencing the phosphorylation of Sgk1 were identified. Both SNPs were synonymous. The prevalence of the first variant, a previously reported SNP at codon 240 in exon 8, did not differ between ESRD patients (16.3%) and controls (15.7%). There was no association between the SNP in exon 8 and either BP within the control population or progression of renal disease in the ESRD population. The second SNP at codon 398 in exon 12 was identified in one patient only. Intron 6 and exon 8 SNPs were in strong linkage disequilibrium, but did not show any association with either BP or renal diseases. CONCLUSIONS: Based on statistical analysis homozygosity for nonconservative mutations in the coding region of the SGK1 gene is estimated at < 1/300 000 when a white Caucasian population is considered, arguing against an important role of mutations of this coding region in hypertension and hypertension-associated progression of renal disease.