Hypertension genetics, single nucleotide polymorphisms, and the common disease: Common variant hypothesis

The investigation of heritable susceptibility to disease is an effort to associate disease phenotype with underlying genotype. Such genotype:phenotype associations have been demonstrated for a large number of monogenetic disorders. The usual strategy has been to use linkage mapping in affected families to identify chromosomal loci from which candidate genes and genotypes can be tested for association with disease. This strategy has not been similarly successful for common heritable disease susceptibilities including hypertension that involve multiple genes and gene-environment interactions. Development of extensive collections of single nucleotide polymorphisms (SNPs) raises the possibility that these SNPs can be used as markers in genome-wide association mapping studies to identify hypertension susceptibility loci. In this approach, large numbers of markers are typed in cases and controls with the expectation that markers interrogating SNPs that are involved in inheritance of disease susceptibility will emerge through their association with this trait in the affected population. Essential hypertension is a common disorder. The term "common" has 2 implications: first, that the disease is prevalent; and, second, that it is widespread. Such frequency and distribution characteristics could arise if the susceptibility alleles for hypertension were prevalent in the founding population of contemporary human beings and became distributed with human global dispersal. This common disease:common variant concept is attractive because it suggests that the genetic heterogeneity underlying hypertension susceptibility could be relatively small. It also allows the possibility that nonrandom association of alleles (linkage disequilibrium, LD) can be used to reduce the number of SNP markers required to identify disease susceptibility alleles because a single marker can act as a surrogate for variation flanking it. The influence of a number of important factors on the detectability of hypertension susceptibility alleles by SNP mapping approaches is not yet fully defined. These factors include the locus and allelic diversity of hypertension, the weaker relationship (compared with Mendelian traits) between genotype and phenotype, the accuracy of high throughput genotyping techniques, the extensive role of nongenetic factors, and the extent and heterogenous nature of LID across the genome.