Association Of Genetic Polymorphisms In Dimethylargine Dimethylaminohydrolase 1 Gene With Essential Hypertension

Essential hypertension (EH) is a multigenic disease with components of environmental and genetic factors. Genetic factors may account for about 30%～60% of blood pressure (BP) variance. The vascular endothelium plays an important role in maintaining the homeostasis of cardiovascular system. It has been reported that endothelial dysfunction is the early characterization of many cardiovascular disease including EH. Nitric oxide (NO) is one of the most important mediators that are involved in the maintainance of vascular endothelium function, and is synthesized from L-arginine catalyzed by NO synthase (NOS). Asymmetric Dimethylarginine (ADMA) is an endogenous inhibitor of NOS which can competitively inhibit NO production. About 80% of ADMA in plasma is metabolized and inactivated by dimethylarginine dimethylaminohydrolases (DDAH1 and DDAH2). Therefore, variation in the DDAH activity may influence NOS activity and consequently NO level through affecting plasma ADMA level. Genes coding for DDAH1 and DDAH2 are important candidates for EH susceptibility.Aims: To investigate the association of DDAH1 genetic polymorphi- sms with EH susceptibility in Chinese Han by a case-control study.Methods: By using the public data deposited in the NCBI database, single nucleotide polymorphisms (SNPs) at DDAH1 locus in Beijing Chinese Han were recorded. After analysis of linkage disequilibrium (LD) and establishment of haplotypes, haplotype tag SNPs (htSNPs) were selected for further study. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to genotype the candidate SNPs. A case-control study of 417 newly diagonised EH patients and 436 normotensive controls of Han nationality recruited from Hunan province was carried out. High-performance liquid chromatography-mass spectum (HPLC-MS) was employed to determine levels of ADMA in plasma. Unconditinal logistic regression was performed to evaluate association of genotypes with EH susceptibility after adjustment for risk factor.Results: (1) A total of 29 common SNPs were deposited in the NCBI database for the Chinese population. 6 major haplotypes with frequencies higher than 5% were inferred from these 29 SNPs. (2) Genotype frequencies for DDAH1 143611 CC,CG and GG genotypes were 57.4%,33.8% and 8.8%, respectively, in cases, and 51.6%,42.1% and 6.3%, respectively, in controls. Significant difference in genotype distribution of C143611G polymorphism was observed (P = 0.046) between cases and controls. Genotype frequencies for DDAH1 144563 CC,TC and TT genotypes were 45.6%, 45.4% and 9.0%, respectively, in cases, and 55.2%, 37.8% and 7.0%, respectively, in controls. Significant difference in genotype distribution of C144563T polymorphism was also observed (P = 0.020) between cases and controls. (3) When adjusted by EH risk factors including sex, age of onset, smoking, alcohol drinking, with or without hyperlipidemia and with or without EH history in the first degree relatives, results of unconditional logistic regression analysis showed that as compared with individuals genotyped as 143611CC, carryiers of the 143611G allele were associated significantly with decreased EH susceptibility (OR=0.701, 95% confidence index [CI]: 0.510-0.962,P=0.028). While as compared with individuals genotyped as 144563CC, carriers of the 144563T allele were associated significantly with increased EH susceptibility (OR=1.474, 95%CI: 1.103-1.969, P=0.009). (4) A significant difference in the frequency distribution of combined genotypes based on both SNPs of C143611G and C144563T was observed between cases and controls (x~2 =18.63, P=0.017), and this difference was resulted from significantly higher frequencies for the combined genotypes 143611CC/144563TC and 143611CC/144563TT in cases as compared with the controls (x~2=7.604, P=0.006). When unconditional Logistic regression for adjustment of EH risk factors was performed, individuals genotyped as 143611CC and carried the 144563T concurrently showed significantly increased EH risk (OR= 1.792, 95%CI: 1.263-2.548, P=0.001). (5) The plasma concentration of ADMA was 0.766±0.230μmol/L in cases, and 0.503±0.181μmol/L in controls, respectively. Cases showed significantly higher plasma ADMA level than controls (P<0.001). (6) In controls, carriers of the DDAH1 143611G allele showed significantly higher mean plasma ADMA level as compared with individuals homozygous for the 143611C allele (P=0.010). While compared with homozygotes of 144563C, carriers of the 144563T allele showed significantly lower mean plasma ADMA level (P=0.041) in controls. When combined genotype based on C143611G and C144563T polymorphisms was considered, 143611C homozygotes carrying the 144563T allele showed significantly lower plasma ADMA level as compared with other combinations in controls (P = 0.015). (7) Neither genotypes of C143611G polymorphism nor genotypes of C144563T polymorphism were associated with plasma ADMA level in EH cases. The combined genotypes based on C143611G and C144563T polymorphisms were not associated with plasma ADMA lever either in the overall cases. However, when the cases were stratified by a positive history of coronary disease, significant difference in mean plasma ADMA level was observed among combined genotypes 143611CC/144563TT (n=5), 143611CC/144563TC (n=17) and other combinations (n=30, P=0.0004).Conclusion: DDAH1 genetic polymorphisms are associated with EH susceptibility in Chinese, and DDAH1 is an important susceptible gene for EH. The plasma ADMA levels are elevated in EH patients. Synergetism between polymorphisms of DDAH1 C143611G and C144563T is existed in affecting plasma ADMA levels as well as EH risk.