Affected relative pairs (primarily sibling pairs) with AAA and no evidence of a family history of a connective tissue disorder were genotyped for 150 highly informative microsatellite polymorphisms marking the autosomal genome at a resolution of 20 cM. The linkage between AAA and these loci was tested using robust affected pedigree member methods to identify genomic regions which might contain genes that predisposed individuals to develop AAA. The existence of predisposing gene(s) were confirmed and their location refined using a defined search strategy, genotyping at increasing levels of resolution, and re-analysis of family data. The predisposing gene(s) were identified by a combination of saturation mapping and molecular analysis of candidate loci. The association of AAA with environmental measures was investigated to determine an equation for estimating risk for relatives of AAA patients based upon environmental measures and genotype. Power calculations based upon the number and structure of families already collected demonstrated the feasibility of identifying genes that predisposed to AAA using this strategy, even in the presence of significant heterogeneity with respect to the loci involved. In addition to identifying genes that were necessary for AAA by linkage analysis, a series of analyses of association were undertaken to identify true susceptibility genes that were neither necessary nor sufficient to cause disease, but which modified an individual's risk of developing AAA.