Introduction 1 1 2 3 2 4 9 10 11 12 16 15 17 19 20 21 22 23 24 24 10 25 28 24 CKD–CV disease link: RAS-cytokine pathway 26 28 29 25 30 32 1 33 10 11 24 34 Fig. 1 Activation of the renin angiotensin system (RAS) and an increase in the local production of angiotensin II (AT2) triggers the inflammatory host response  10 10 35 36 37 38 39 40 41 42 43 44 45 25 32 46 24 47 Genetic polymorphisms 1 48 Table 1 Glossary of common genetic terms Alleles: Biological pathway: Candidate gene: Epigenetics: Genome: Genotype: Haplotype: Heterozygous: Homozygous: Phenotype: Polymorphisms: Tag SNPs: 49 50 www.ncbi.nlm.nih.gove/projects/SNP/ 2 . Table 2 Candidate-gene polymorphisms and associations with renal and cardiovascular (CV) diseases among subjects with chronic kidney disease (CKD) Author a b n Clinical significance Renin Angiotensin System (RAS) 53 ACE haplotypes US diabetic nephropathy CKD (DCCT-EDIC)/cohort study Restricted to Caucasian cohort = 1,365 The genetic variation of the ACE gene is associated with microalbuminuria and diabetic nephropathy. 49 ACE insertion/deletion polymorphism European diabetic nephropathy CKD/case-control study Adult diabetic nephropathy cases = 1,057, controls = 1,127 The haplotype including the ACE deletion allele was associated with diabetic nephropathy. 57 ACE insertion/deletion polymorphism European Vesicoureteral reflux CKD/case-control study Pediatric VUR cases = 77, controls = 80 A deletion at both alleles is linked to renal scarring in VUR. 55 ACE insertion/deletion polymorphism European CKD (Nutritional Treatment of Chronic Renal Failure in Childhood Study)/cohort study Pediatric cohort = 95 A deletion at both alleles is linked to a higher risk of renal progression among children with congenital renal malformation. 58 ACE insertion/deletion polymorphism European ESRD/case-control study Adult ESRD cases = 260, controls = 327 A deletion at both alleles is linked to a higher risk of renal progression among adults. 54 ACE insertion/deletion haplotype US diabetic nephropathy CKD/case-control study Adult Caucasians type 2 with diabetic nephropathy cases = 291, controls = 167 The deletion allele haplotype is associated with diabetic nephropathy. 56 ACE insertion/deletion polymorphism European ESRD/case-control study Pediatric ESRD cases = 20, controls = 150 A deletion at both alleles is linked to ESRD. 64 AGT-6 G>A US CKD (ARIC Study)/ cohort study c Genotype A/A is linked to a higher risk of renal progression among African American CKD patients. 111 AGT M235T European kidney transplant/case-control study Adult kidney transplant cases = 82, controls = 100 Genotype Thr/Thr linked to chronic allograft dysfunction. 66 AT1R A>C European ESRD/case-control study Adult ESRD cases = 745, controls = 520 Genotype C/C or A/C is linked to higher risk of renal progression in adults. Interleukin (IL)-1 73 IL-1α g.-889 C>T US ESRD/case-control study Adult ESRD cases = 239, controls = 252 Genotype T/T is linked with risk for ESRD. 82 IL-1β g.-511 C>T European Henoch-Schonlein purpura disease (HSP)/case-control study Adult and pediatric HSP cases = 49, controls = 146 Carriage of the T allele linked to severity of renal involvement with Henoch-Schonlein purpura. Interleukin-1 Receptor Antagonist 83 IL-2RN*2 European ESRD/case-control study Adult ESRD cases = 602, controls = 433 Homozygous for the IL2RN*2 allele linked with more rapid progression in patients with glomerulonephritis and diabetic nephropathy and risk for ESRD. 73 IL-1RN*2 US ESRD/case-control study Adult ESRD cases = 239, controls = 252 Homozygous for the IL2RN*2 allele is linked to risk for ESRD. 81 IL-12N*2 Japanese IgA nephropathy CKD /case-control study Adult IgA Nephropathy cases = 106, controls = 74 Carriage of the IL2RN*2 allele is linked to severe proteinuria and increased creatinine in IgA nephropathy. Interleukin-6 72 g.-174G>C US ESRD (HEMO Study)/cross-sectional study Adult ESRD cohort = 187 Genotype G/G or G/C is linked to increased comorbid conditions and decreased functional status among dialysis patients. 86 g.-174G>C European ESRD/case-control study Adult ESRD cases = 161, controls = 169 Carriage of the C allele linked to LVH in hemodialysis patients, especially those with diabetes. 87 g.-174G>C European Kidney transplant/cohort study Adult kidney transplant cohort = 158 Carriage of the C allele linked to decreased kidney allograft survival. Interleukin-10 88 g.-1082 G>A European ESRD/cohort study Adult ESRD cohort = 300 The A/A genotype is linked to a lower production of IL-10 and increased CV morbidity Tumor Necrosis Factor (TNF)-α 72 g.-308 G>A US ESRD (HEMO Study)/cross-sectional study Adult ESRD cohort = 187 Genotype A/A or A/G is linked to low serum albumin, increased comorbid conditions, and decreased functional status among dialysis patients. Transforming Growth Factor-β 106 g.-509C>T and g.+869T>C Japanese IgA Nephropathy CKD/cross-sectional study Adult IgA nephropathy cases = 329, controls = 297 The -509C/C and 869C/C genotypes are linked with heavy proteinuria and mesangial cell proliferation in patients with IgA nephropathy. 107 g.+915G>C US ESRD (HEMO Study)/cross-sectional, and cohort studies Adult ESRD cohort = 187 Genotype G/C vs G/G was linked with risk for prevalent vascular disease, new onset cardiac morbidity and cardiac mortality in HD patients. Plasminogen Activator Inhibitor (PAI)-1 113 4G/5G European ESRD/cohort study Adult ESRD cohort = 417 Genotype 4G/4G is linked to increased risk for fatal MI among HD patients. 111 4G/5G European Kidney transplant/case-control study Adult kidney transplant cases = 82, controls = 100 Carriage of the 4G allele linked to chronic allograft dysfunction. 112 4G/5G Chinese Systemic lupus erythematosus CKD/case-control study Adult diabetic nephropathy cases = 95, controls = 46 Genotype of the 4G/4G linked to increased severity lupus nephritis among SLE patients. ACE  AGT  AT1R  DCCT  EDIC  ESRD  ARIC  HEMO  VUR  HD  SLE MI a b c The renin-angiotensin system 51 52 30 49 53 54 55 58 59 60 61 62 63 64 65 66 67 68 Interleukin-1 and IL-1 receptor antagonist (IL-1Ra) 69 70 71 72 73 73 74 75 76 73 77 78 80 78 80 81 83 Interleukin-6 (IL-6) 84 84 85 47 86 87 Interleukin-10 (IL-10) 47 88 89 90 88 Tumor necrosis factor-α (TNF-α) 91 92 93 94 95 96 47 Transforming growth factor-β (TGF-β) 97 98 99 10 10 100 101 102 103 104 105 106 107 Plasminogen activator inhibitor-1 (PAI-1) 108 108 109 110 111 112 113 55 57 Finding the link between genotype and phenotype 47 3 . Table 3 72 Cytokine Genotype Transcription/secretion level (expected) Plasma level in pg/ml mean ± SD Interleukin (IL)-6 -174 C/C Low 12.2 ± 5.1 -174 G/G, G/C High a Tumor necrosis factor (TNF)-α -308 G/G Low 998.8 ± 1156.2 -308 G/A, A/A High 1131 ± 1616.2 IL-10 -1082 A/A Low 344.8 ± 356.3 -1082 G/A Intermediate 391.0 ± 440.5 -1082 G/G High b a  p b  p 24 114 115 Haplotype and HapMap http://www.hapmap.org 116 117 118 119 120 Potential limitations of gene association studies P −6 121 Type I and type II error 122  P 123 125  P 126  P 126  P P −6 121 126 127  P 122 124 128 129 130 131 132 132 131 125 Limitations in study design 122 125 133 134 135 125 136 133 134 137 134 134 134 Conclusions Genetic association studies have the potential to provide new insights into the factors responsible for CKD renal and CV progression. These investigations provide hope for new drug targets to treat or modify individual disease risk. In the case of CKD, genetic polymorphisms in the RAS–cytokine pathway may be responsible for the intraindividual variation in renal and cardiac progression in patients with CKD and may offer new targets for drug therapy. The Human Genome and HapMap projects have made it possible to evaluate a multitude of candidate genes that might be linked to CKD progression. The enthusiasm for these investigations must be tempered by acknowledging the limitations of gene association studies. Attention to biologic plausibility and appropriate study design will help the interpretability of published results. Independent investigations replicating initial findings are needed to support an inference of a causal association between the gene polymorphism of interest and the disease phenotype. 49 50 138 139