Each collaborating investigator is responsible for an essential element of the network: Eric Boerwinkle for genotyping and linkage analyses, Robert Ferrell for genotyping, Craig Hanis for recruiting Mexican-Americans, Richard Hutchinson for recruiting African-Americans, Sharon Kardia for cladistic and prediction analyses and data management, and Stephen Turner for recruiting Non-Hispanic whites and measuring physiologic variables. Between 1995 and 2000, the network carried out five specific aims to localize and characterize the genetic determinants of high blood pressure. Aim 1 used robust sibling pair linkage methods in 500 hypertensive sibling pairs in each racial group (a total of 1,500 sibling pairs) to localize genes influencing interindividual differences in the occurrence of essential hypertension. Aims 2 and 3 took advantage of previously collected blood pressure and intermediate predictor trait data from 1,488 normotensive sibling pairs from the Rochester Family Heart Study to localize genes contributing to essential hypertension. The linkage analyses (Aims 1-3) used both an extensive array of candidate genes and a large number of anonymous markers throughout the genome. Aim 4 used multiple diallelic sequence polymorphisms and cladistic analyses within a linked gene to identify haplotypes for further DNA sequencing in order to identify candidate functional DNA sequence variation contributing to interindividual differences in BP levels and essential hypertension status. Aim 5 evaluated the ability of candidate functional DNA sequence variation to predict essential hypertension status in the three racial groups.
The study was renewed in September 2000 to pursue two lines of investigation. The first is to identify and characterize genes contributing to atherosclerotic coronary heart disease using electron beam computed tomography (EBCT) to quantify coronary artery calcification as a measure of preclinical disease. Robust sibling-pair linkage methods will be used to determine whether any of the more than 375 highly polymorphic tandem repeat marker loci spanning the genome are linked to genes influencing EBCT measures of coronary artery calcification in at least 500 GENOA sibships from Rochester, Minnesota. Association analysis will be used to determine whether biallelic markers of DNA sequence variation in candidate genes identified by GENOA or others to influence blood pressure level or diagnostic category also influence EBCT measures of coronary artery calcification in at least 500 GENOA participants from Rochester, Minnesota. The second line of investigation extends analytical methods (linkage disequilibrium regression and combinatorial partitioning) to more finely localize positional candidate genes and loci, and to identify gene-gene and gene-environment interaction effects influencing the measured Family Blood Pressure Program and GENOA phenotypes.