PKD2 and connective tissue disorder: Among the initial candidate genes discovered in gene expression and genome-wide linkage analyses are type III collagen (COL3A1), endoglin (ENG), fibrillin (FBN1), α1-antitrypsin (SERPINA1) and polycystin (PKD1, PKD2) (Nahed et al., 2007; Zhou et al., 2018), supporting observations of increased risk for IA formation in individuals with connective tissue disorders or PKD.