GRK4 and hypertensive disorder: Although there were no differences in NOS3 genotype distribution according to the levels of blood pressure in both subgroups CENT p = 0.554 and CONT p = 0.069, a high degree of synergy was detected between hypertension grade and NOS3 genotype and also, an epistatic interaction although less strong than the latter was observed between ANG and GRK4 genotypes for longevity (Figure 3(a)).