6. Candidate gene studies
Candidate genes are chosen for their assumed role in the pathogenesis of hypertension and can derive from experimental models or knowledge of the pathophysiology. The most plausible candidate genes are components of the renin–angiotensin–aldosterone system and genes involved in signal transduction (e.g. the G-protein subunit-β3 gene GNB3), salt and water handling (e.g. the adducin-α genes ADD1), regulation of vascular tone (e.g. the endothelial nitric oxide synthase gene NOS3) and production of or defences against oxidative stress. However, despite numerous reports on association in small and medium sized cohorts since publication of our previous review [14] there has been little evidence for a substantial association of any of these genes or single nucleotide polymorphisms (SNPs) within these genes with hypertension. The main reasons for this lack of positive results are (1) the individual contribution of genetic variants to the blood pressure phenotype is small; (2) most of the study designs lacked power to detect these small effects; (3) inconsistency of phenotyping did not allow results to be compared or combined; (4) selection of candidate genes depended on known pathways of blood pressure regulation precluding undiscovered pathways; (5) most of the candidate gene studies tended to be single SNP studies which was not completely informative of the gene variations and additional SNP identification needed sequencing resources which were not readily accessible; (6) studies of rare frequency variants were not done; and (7) the study design issues mentioned above precluded any meaningful study of gene–gene or gene–environment interactions. Nevertheless, the candidate gene approach remains one of the cornerstones of studies into the genetics of hypertension. We refer to recent reviews on the genetics of the renin–angiotensin–aldosterone system [63], [64] and [65], G-proteins [66], adducin [67], and oxidative stress [68] and [69] in hypertension, but will discuss the association of the aldosterone synthase gene (CYP11B2) with hypertension as an exemplar.
6. Candidate gene studiesCandidate genes are chosen for their assumed role in the pathogenesis of hypertension and can derive from experimental models or knowledge of the pathophysiology. The most plausible candidate genes are components of the renin–angiotensin–aldosterone system and genes involved in signal transduction (e.g. the G-protein subunit-β3 gene GNB3), salt and water handling (e.g. the adducin-α genes ADD1), regulation of vascular tone (e.g. the endothelial nitric oxide synthase gene NOS3) and production of or defences against oxidative stress. However, despite numerous reports on association in small and medium sized cohorts since publication of our previous review [14] there has been little evidence for a substantial association of any of these genes or single nucleotide polymorphisms (SNPs) within these genes with hypertension. The main reasons for this lack of positive results are (1) the individual contribution of genetic variants to the blood pressure phenotype is small; (2) most of the study designs lacked power to detect these small effects; (3) inconsistency of phenotyping did not allow results to be compared or combined; (4) selection of candidate genes depended on known pathways of blood pressure regulation precluding undiscovered pathways; (5) most of the candidate gene studies tended to be single SNP studies which was not completely informative of the gene variations and additional SNP identification needed sequencing resources which were not readily accessible; (6) studies of rare frequency variants were not done; and (7) the study design issues mentioned above precluded any meaningful study of gene–gene or gene–environment interactions. Nevertheless, the candidate gene approach remains one of the cornerstones of studies into the genetics of hypertension. We refer to recent reviews on the genetics of the renin–angiotensin–aldosterone system [63], [64] and [65], G-proteins [66], adducin [67], and oxidative stress [68] and [69] in hypertension, but will discuss the association of the aldosterone synthase gene (CYP11B2) with hypertension as an exemplar.
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