Genotype-phenotype relationships for the renin-angiotensin-aldosterone system in a normal population

The renin-angiotensin-aldosterone system plays an important role in blood p ressure regulation by influencing salt-water homeostasis and vascular tone. The purpose of the present study was to search for associations of single nucleotide polymorphisms on 3 major candidate genes of this system with the plasma concentrations of the corresponding renin-angiotensin-aldosterone s ystem components considered as quantitative phenotypes. Genotyping was perf ormed in 114 normotensive subjects for different variants of the angiotensi nogen (AGT) gene (C-532T, G-6A, M235T), the angiotensin I-converting enzyme (ACE) gene [4656(CT)(2/3)], the aldosterone synthase (CYP11B2), and the ty pe 1 angiotensin II receptor (AT1R) gene (A1166C) by hybridization with all ele-specific oligonucleotides (ASO) or enzymatic digestion of polymerase ch ain reaction products. Plasma levels of AGT, ACE, angiotensin II (Ang II), aldosterone, and immunoreactive active renin were measured according to sta ndard techniques. Platelet binding sites for Ang II were analyzed by the bi nding of radioiodinated Ang II to purified platelets. B-max and K-D values of the Ang II binding sites on platelets of each individual were calculated to examine a possible relationship between these parameters and the AT1R g enotype. A highly significant association of the ACE 4656(CT)(2/3) variant with plasma ACE levels was observed (P<0.0001). ANOVA showed a significant effect of the AGT C-532T polymorphism on AGT plasma levels (P=0.017), but n o significant effect was detectable with the other AGT polymorphisms tested , such as the G-6A or the M235T. A significant effect association was also found between the C-344T polymorphism of the CYP11B2 gene and plasma aldost erone levels, with the T allele associated with higher levels (P=0.02). No genotype effect of the AT1R A1166C polymorphism was detected either on the B-max or the K-D value of the Ang II receptors on platelets.