Beta-fibrinogen haplotypes and the risk for cardiovascular disease in a dialysis cohort

Antihypertensive pharmacogenetic effect of fibrinogen-beta variant -455G>A on cardiovascular disease, end-stage renal disease, and mortality: the GenHAT study

OBJECTIVE

The FGB gene codes for fibrinogen-beta, a polypeptide of the coagulation factor fibrinogen, which is positively associated with cardiovascular diseases. Studies show that angiotensin-converting enzyme (ACE) inhibitors lower plasma fibrinogen concentrations, whereas diuretics and calcium-channel blockers do not. As carriers of the FGB-455 minor 'A' allele have higher levels of fibrinogen while ACE inhibitors lower it, we hypothesize that 'A' allele carriers benefit more from antihypertensive treatment with ACE inhibitors than calcium-channel blockers or diuretics, relative to 'GG' genotype individuals.

METHODS

The Genetics of Hypertension Associated Treatment (GenHAT) study [ancillary to Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT)] genotyped hypertensive participants for several hypertension-related candidate genes, making this a post-hoc analysis of a randomized trial. In total, 90.1% of the ALLHAT population was successfully genotyped for FGB-455. We included participants (n=30 076) randomized to one of three antihypertensive medications (lisinopril, amlodipine, chlorthalidone), with two treatment comparisons: lisinopril versus chlorthalidone and lisinopril versus amlodipine. The primary outcome of ALLHAT/GenHAT was coronary heart disease, defined as fatal coronary heart disease or non-fatal myocardial infarction, and secondary outcomes included stroke, heart failure, all-cause mortality, and end-stage renal disease (ESRD) with mean follow-up time of 4.9 years. Genotype-by-treatment interactions (pharmacogenetic effects) were tested with the Cox regression.

RESULTS

Stroke: common 'GG' homozygotes had higher risk on lisinopril versus amlodipine [hazard ratio (HR)=1.38, P<0.001], whereas minor 'A' allele carriers had slightly lower risk (HR=0.96, P=0.76; P value for interaction=0.03). Mortality: 'GG' homozygotes had higher risk on lisinopril versus amlodipine (HR=1.12, P=0.02) or chlorthalidone (1.05, P=0.23), whereas 'A' allele carriers had slightly lower risk (HR=0.92, P=0.33 for lisinopril versus amlodipine; HR=0.88, P=0.08 for lisinopril versus chlorthalidone; P value for interactions 0.04 and 0.03, respectively). ESRD: 'GG' homozygotes had higher risk on lisinopril versus chlorthalidone (HR=1.27, P=0.08), whereas 'A' allele carriers had lower risk (HR=0.64, P=0.12; P value for interaction=0.03).

CONCLUSION

There was evidence of pharmacogenetic effects of FGB-455 on stroke, ESRD, and mortality, suggesting that relative to those homozygous for the common allele, variant allele carriers of the FGB gene at position -455 have a better outcome if randomized to lisinopril than chlorthalidone (for mortality and ESRD) or amlodipine (for mortality and stroke). For the models in which a pharmacogenetic effect was observed, the outcome rates among 'GG' homozygotes were higher in those randomized to lisinopril versus amlodipine or chlorthalidone, whereas minor 'A' allele carriers had lower event rates when randomized to lisinopril versus the other medications.

Reliability of high-throughput genotyping of whole genome amplified DNA in SNP genotyping studies

Whole genome amplification (wga) of DNA is being widely implemented in many laboratories to extend the life of samples only available in limited quantities for genetic analysis. We determined the reliability of wgaDNA genotypes in three sets of replicates from the same individuals: (i) 23 pairs of genomic DNA (gDNA), (ii) 43 pairs gDNA versus wgaDNA, and (iii) 29 pairs of independently amplified wgaDNA. Amplification was performed using multiple displacement amplification (MDA). Genotyping was successful for both DNA types for 1268 out of 1534 SNPs from 164 cardiovascular candidate genes assayed in a single Illumina panel. Amplified DNA failed for 77 SNPs (6%) that were genotyped successfully with genomic material. Percent of successful SNP calls, and concordance between pairs and kappa statistics (kappa) were determined. A total of 54 110 genotypes from gDNA-wgaDNA pairs were available for concordance analysis. Mean kappa for gDNA-wgaDNA pairs was 0.99. Concordance between gDNA-wgaDNA pairs was higher than amongst wgaDNA pairs (mean kappa for the 29 independently amplified pairs of wgaDNA was 0.95; interquartile range: 0.93-1.00). A statistical analysis of those SNPs which failed to genotype from amplified DNA only revealed that those loci were more likely to be closer to the telomeres and in locally GC-rich sequences. In summary, the MDA method produces wgaDNA samples that can be genotyped using high-throughput technology with a very high reproducibility to the original DNA but with slightly lower call rates. DNA amplification methodologies provide a useful solution for current and future large-scale genetic analyses especially with limited quantities of samples and DNA.

Gene polymorphism association studies in dialysis: vascular access

Complications of the vascular access site for hemodialysis are a major cause of morbidity, suboptimal dialysis, and hospitalization. Vascular access for dialysis that is achieved by central venous catheters is associated with complications such as infection and thrombosis. Arteriovenous fistulas and grafts are also at risk for infectious complications. Further, proliferation of the venous wall with secondary thrombosis is a common pathophysiological process that leads to vascular access dysfunction. Genetic polymorphisms that contribute to vascular access failure are found among factors of the coagulation cascade, and host mediators that induce endothelial dysfunction as well as vessel wall proliferation. The two most common mutations of coagulation factors seem to influence the risk of central venous catheter and fistula thrombosis. Indeed, both the single nucleotide polymorphism of the factor V gene at amino acid position 506 (factor V Leiden mutation) and the prothrombin 20210 polymorphism have been associated with thrombotic complications of the vascular access. Among the endothelium-directed factors, a polymorphism of the methylene tetrahydrofolate reductase gene coding for an enzyme that degrades the endothelium toxic product homocysteine, has been associated with fistula failure. While the angiotensin converting enzyme polymorphism does not seem to be associated with vascular access complications, polymorphisms of the profibrogenic cytokine transforming growth factor-beta1 are associated with the prognosis of native arteriovenous fistulae. The role of pro- and anti-inflammatory cytokine gene polymorphisms as prognostic factors for vascular access is yet to be clearly defined.

AMI is associated with polymorphisms in the NOS3 and FGB but not in PAI-1 genes in young adults

BACKGROUND

We investigated the relationship between NOS3, FGB and PAI-1 polymorphisms and endothelial dysfunction and risk factors for acute myocardial infarction (AMI) in young adults.

METHODS

Endothelial function was measured by response to flow mediated vasodilation (FMV) and induced by nitrate (FMN). Biochemical parameters were measured by standard enzymatic methods and plasma total nitrate was analyzed by the NOA system. NOS3 (T-786C, G894T and intron 4A/B STR), FGB (C-148T and G-455A) and PAI-1 (4G/5G) polymorphisms were determined by PCR-RFLP.

RESULTS

Concentrations of total and LDL cholesterol, apo B, triglycerides, nitrate, PAI-1 and fibrinogen were higher and apo AI, HDL cholesterol and FMV were lower in AMI patients than in controls (p<0.001). PAI-1 (p<0.001) but not nitrate was higher in AMI patients with low response to FMV. NOS3 T-786C and FGB C-148T polymorphisms were associated with AMI (p<0.050). NOS3 T-786C was also related to hypertension (p=0.049). NOS3 intron 4A/B STR was associated with increased concentrations of total cholesterol and apo B. NOS3-786TT/894GT haplotype was associated with increased FMV (p=0.018) than the other haplotypes.

CONCLUSIONS

Our data suggest NOS3 and FGB polymorphisms are associated with AMI. NOS3 is also related to hypertension, endothelial dysfunction and variation on serum cholesterol in young adults with AMI.