Clinical Significance Of Angiotensin Converting Enzyme Gene Insertion/Deletion Polymorphism

Angiotensin converting enzyme is a membraneous glycoprotein constituent of vascular endothelial cells. It presents in tissue and body fluid. It occurs in a circulating form and as an ectoenzyme bound to cell membranes. ACE catalyzes the cleavage of carboxy-terminal dipeptidyl residues. Its physiological function is to catalyze the cleavage of histidyl-leucine from angiotensin I to yield angiotensin II. Another main function of ACE is the inactivation of bradykinin. Thus, ACE plays an important role in RAAS and bradykinin system as well. It is a focus to investigate ACE and its gene polymorphism.Objective: Recently the methods for determining serum ACE are improved, and the variety in serum activity of ACE has been valuable in the diagnosis of many disease. ACE gene is locus on chromosome 17q23, including 26 extrons and 25 introns. An insertion / deletion polymorphism of angiotensin converting enzyme gene has been described which is based on the presence(insertion) or absence (deletion) of a 287-base pair Alu-repeat DNA domain, resulting in the three genotypes homozygous DD, heterozygous DI, and homozygous I I. The aim of this study is investigate the relationship among the ACE activity, ACE gene I/D polymorphism and diseases such as diabetic nephropathy and cerebral stroke.Methods: 61patients meeting the criteria of type 2 diabetic mellitus and 48 patients with overt nephropathy were recruited;131 patients with cerebral stroke and 52 hyperpietics were recruited. The control group includes 50 age-match health cases. The I/D polymorphism of ACE gene was analyzedwith PCR amplification. The PCR fragments were separated on the horizontal 2% agarose gel by electrophoresis and visualized by staining with EB. All the patients and controls serum ACE activity were measured simultaneously. Some relative clinical data were collected. To avoid the mistyping, we used both DMSO and an insertion-specific primer, and compared the results of the two methods.Results:l)Diabetic nephropathy: The frequency of the ACE DD genotype in the patients with diabetic nephropathy was significantly higher than in the control group ( x 2=8.052 , P=0.005 ) , but similar to the diabetics. To determine whether ACE gene polymorphism was associated with the severity of diabetic nephropathy, we divided patients with diabetic nephropathy into dialysis and non-dialysis groups. But there was no difference in the frequency of DD genotype between two groups. The serum ACE activity was higher in DD homozygotes than in I I homozygotes, with intermediate values in DI heterozygotes. Those with diabetic nephropathy had increased ACE activity.2) Cerebral Stroke: The frequencies of DD genotype and D allele in the patients with cerebral stroke , including infarction and hemorrhage, was higher than normal controls. The frequencies of DD genotype and D allele in the cerebral infarction with hypertension group, cerebral hemorrhage with hypertension were higher than the control group. There was no difference in ACE activity between cerebral stroke group , hyperpietics group and control group.3) Methodology: In heterozygotes the I allele may be difficult to detect, thus overestimating DD frequency. It can be circumvented by adding 5% dimethylsulfoxide in the PCR or repeating the PCR with intron-specific primers. And these two methods have the same result in preventing mistyping of DI as DD genotypes.7Conclusions: 1) The DD genotype of ACE gene attributes to the susceptibility of diabetic nephropathy. The detection of ACE activity is useful for the diagnosis and therapy.2) There was a positive association between the D allele of the ACE polymorphism and cerebral stroke.3) The ACE gene I/D polymorphism regulates the activity of serum ACE.4) The mistyping of DI as DD genotypes was present. It could be circumvented by repeating the PCR with intron-specific primers or adding 5%DMS0, and there was no difference between them.