Neuropeptide Y gene polymorphisms and chronic kidney disease progression

Background:Neuropeptide Y (NPY) is a neurotransmitter expressed in both the central and peripheral nervous systems, which is involved in regulating a multitude of physiological processes ranging from arterial pressure, energy balance, the immune response and inflammation and renal electrolyte transport. In a cohort of chronic kidney disease (CKD) patients, we recently showed that high plasma NPY levels predict renal disease progression independently of hypertension and other risk factors but the causal nature of this association remains unproven.Methods:In the same cohort of the previous study, we tested the relationship of NPY gene variability, as assessed by five single nucleotide polymorphisms (SNPs) that explained the whole gene variability, with the incidence rate of a predefined combined renal endpoint (dialysis/transplantation/estimated glomerular filtration rate reduction >30%) over a median follow up of 36months (inter-quartile range 35-37months) in 735 ethnically homogeneous patients with stage 2-5 CKD.Results:Two variants [rs16131 (recessive model for the T risk allele: TT, n=563; CT + CC, n=172) and rs16140 (dominant model for the G risk allele: GG + CG, n=413; CC, n=322)] were coherently associated with the incidence rate of renal events [hazard ratio (HR) ranging from 1.39 to 1.57, P <= 0.015] and this was also true when the two SNPs were jointly introduced into the same Cox model (P <= 0.043). The analysis of the biological interaction showed a significant synergism between the NPY rs16131 and rs16140 variants. Indeed, patients harboring NPY rs16131 TT and NPY rs16140 GG + CG risk genotypes had a much higher HR of renal events [HR: 1.80, 95% confidence interval (CI):1.16-2.79, P=0.009] than that expected in the absence of biological interaction under both the additive and multiplicative models and the attributable proportion due to interaction (AP) was 25% and 38% on crude and adjusted analyses, respectively.Conclusion:This study, based on the Mendelian randomization approach and using NPY gene variants as instrumental variables to test the link between NPY and CKD progression, is in line with findings indicating that high plasma NPY levels predict an increased risk for renal events and lend support to the hypothesis that NPY is causally involved in renal disease progression.