Multilocus analysis of hypertension: a hierarchical approach

While hypertension is a complex disease with a well-documented genetic component, genetic studies often fail to replicate findings. One possibility for such inconsistency is that the underlying genetics of hypertension is not based on single genes of major effect, but on interactions among genes. To test this hypothesis, we studied both single locus and multilocus effects, using a case-control design of subjects from Ghana. Thirteen polymorphisms in eight candidate genes were studied. Each candidate gene has been shown to play a physiological role in blood pressure regulation and affects one of four pathways that modulate blood pressure: vasoconstriction (angiotensinogen, angiotensin converting enzyme - ACE, angiotensin II receptor), nitric oxide (NO) dependent and NO independent vasodilation pathways and sodium balance (G protein-coupled receptor kinase, GRK4). We evaluated single site allelic and genotypic associations, multilocus genotype equilibrium and multilocus genotype associations, using multifactor dimensionality reduction (MDR). For MDR, we performed systematic reanalysis of the data to address the role of various physiological pathways. We found no significant single site associations, but the hypertensive class deviated significantly from genotype equilibrium in more than 25% of all multilocus comparisons (2,162 of 8,178), whereas the normotensive class rarely did (11 of 8,178). The MDR analysis identified a two-locus model including ACE and GRK4 that successfully predicted blood pressure phenotype 70.5% of the time. Thus, our data indicate epistatic interactions play a major role in hypertension susceptibility. Our data also support a model where multiple pathways need to be affected in order to predispose to hypertension.

Combinations of variations in multiple genes are associated with hypertension

The genetic analysis of hypertension has revealed complex and inconsistent results, making it difficult to draw clear conclusions regarding the impact of specific genes on blood pressure regulation in diverse human populations. Some of the confusion from previous studies is probably due to undetected gene-gene interactions. Instead of focusing on the effects of single genes on hypertension, we examined the effects of interactions of alleles at 4 candidate loci. Three of the loci are in the renin-angiotensin-system, angiotensinogen, ACE, and angiotensin II type 1 receptor, and they have been associated with hypertension in at least 1 previous study. The fourth locus studied is a previously undescribed locus, named FJ. In total, 7 polymorphic sites at these loci were analyzed for their association with hypertension in 51 normotensive and 126 hypertensive age-matched individuals. There were no significant differences between the 2 phenotypic classes with respect to either allele or genotype frequencies. However, when we tested for nonallelic associations (linkage disequilibrium), we found that of the 120 multilocus comparisons, 16 deviated significantly from random in the hypertensive class, but there were no significant deviations in the normotensive group. These findings suggest that genetic interactions between multiple loci rather than variants of a single gene underlie the genetic basis of hypertension in our study subjects. We hypothesize that such interactions may account for the inconsistent findings in previous studies because, unlike our study, prior studies almost always examined single-locus effects and did not consider the effects of variation at other potentially interacting loci.

Surgery for Aortic Arch Thrombosis

A localized thrombus involving the ascending aorta and arch rarely occurs in the absence of an underlying etiology such as chest trauma, atherosclerosis, a hypercoagulable state or instrumentation. A review of the literature between 1966 - 2003 yielded 38 reported cases of localized aortic arch thrombi, 21 of which were treated by surgical excision of the thrombus using different approaches. In this communication, we describe this clinical entity, with its diagnosis and management. The technical details that are important to ensure the safe conduct of the procedure are discussed.

Serum lipid and lipoprotein levels in Ghanaians with diabetes mellitus and hypertension

Both diabetes mellitus and hypertension alter lipid and lipoprotein metabolism and increase the risk of coronary artery disease. We have reported previously on lipid and lipoprotein levels in healthy Ghanaians, and this study deals with the levels of these biochemical parameters in Ghanaians with diabetes mellitus and hypertension. Fasting serum lipoproteins were determined on blood samples drawn from healthy male and female Ghanaians as well as age-matched individuals with either diabetes or hypertension. Cholesterol, high-density lipoprotein cholesterol (HDL-C), triglycerides, and fasting blood glucose were measured. Low-density lipoprotein cholesterol (LDL-C) and very low-density lipoprotein cholesterol (VLDL-C) were derived. Total serum cholesterol levels were 4.43 +/- 0.22 mmol/L and 4.67 +/- 0.26 mmol/L for diabetic males and females, respectively. High-density lipoprotein was 1.55 +/- 0.09 mmol/L and 1.50 +/- 0.09 mmol/L for male and female diabetics, respectively. Lipid and lipoprotein levels in the hypertensive patients did not differ from the above values. The levels of cholesterol and lipoprotein obtained in Ghanaians with hypertension and diabetes mellitus were similar to those of their age-matched healthy controls. These results suggest a reduced risk of coronary artery disease from the atherogenic effects of cholesterol in Ghanaians with diabetes mellitus and hypertension.