(Hypertension. 1996;28:912-915.)
© 1996 American Heart Association, Inc.
Articles |
The Role of Genetic Polymorphisms of Angiotensin-Converting Enzyme in the Progression of Renal Diseases
the Renal Unit, Glasgow Royal Infirmary (K.J.M., M.B.J.-J.) and Western Infirmary (P.N.H., A.G.J.), and the Departments of Medicine and Therapeutics, Western Infirmary (S.U., J.M.C.C., A.G.J.), Glasgow, Scotland.
Correspondence to Dr Alan Jardine, Lecturer in Nephrology, Department of Medicine and Therapeutics, Western Infirmary, Glasgow G11 6NT, UK. E-mail a.g.jardine@clinmed.gla.ac.uk.
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Abstract |
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The renin-angiotensin system is likely to be important in the progression of renal diseases because of its effect on tissue hemodynamics and glomerular cell function. Recent evidence from small studies has suggested a possible role for the genetic determinants of angiotensin converting enzyme activity in the rate of progression of renal failure. We studied the effect of the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme gene on the rate of renal function deterioration in 822 patients with a variety of renal diseases. We found that the slope of the reciprocal serum creatinine–versus-time plot was steeper in patients homozygous for the deletion allele (DD) compared with those homozygous for the insertion allele (II) (P=.015). When patients with similar renal function at presentation (creatinine <200 µmol/L) were compared, II homozygotes had significantly improved renal survival (P=.039). Separate analyses of patients with glomerular diseases and tubulointerstitial diseases demonstrated an effect of this genotype in glomerular diseases only. These data provide further evidence of the possible role of the angiotensin-converting enzyme gene in the rate of progression of renal failure, although further studies are required to evaluate the role of this and other proposed candidate genes in renal diseases.
Key Words: polymorphism • renal disease • angiotensin-converting enzyme
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Introduction |
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The RAS is involved in the regulation of arterial BP and local tissue hemodynamics. The activity of this system is regulated by the rate of production of angiotensinogen and the activity of both renin and the ACE. The effects of the RAS are mediated by Ang II via its actions as a growth factor and pressor hormone. Genetic variation in the production of Ang II by the RAS has been proposed to contribute to the development of diseases such as hypertension and atherosclerosis. Recently, several studies have identified functional polymorphisms in the RAS, and polymorphic markers in the genes for angiotensinogen and ACE have been associated with the development of hypertension and cardiovascular disease.1 2 3 4 5
In the kidney Ang II also regulates cell growth and matrix production,6 which together with its hemodynamic effects may promote progression of renal disease. Studies have suggested a potential role for genetic polymorphisms in the RAS in the development of diabetic nephropathy and nondiabetic renal disease.7 8 9 Specifically, the insertion/deletion polymorphism in ACE that is associated with higher levels of circulating and tissue ACE and an enhanced response to exogenous Ang I has been associated with IgA nephropathy and diabetic nephropathy.10 11 12
In the present study we investigated whether these limited observations could be extended to all patients with primary renal disease by studying the relationship between ACE gene polymorphism and the natural history of renal disease in 882 patients with primary renal disease.
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Methods |
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Patients on RRT (ie, dialysis or transplantation) or those attending the renal clinic at two Glasgow teaching hospitals were included in the study. Clinical information was retrieved retrospectively from computerized hospital and biochemical records and included age at presentation, presenting creatinine level, SBP, DBP, protein excretion, and number of antihypertensive drugs being taken at the time of presentation. The rate of progression of renal failure was calculated by the least-squares regression method of reciprocal creatinine versus time.13 Only those patients who were followed up for >1 year, for whom there were >5 data points, and for whom the slope of the regression line could be fitted with a value of P<.01 were included. Ethics committee approval was granted for the study from both centers. The control population (n=371) included healthy volunteers and patients who were attending the Ophthalmology Outpatient Department with eye trauma; their median age was the same as that in the study population.
Genotyping
ACE genotyping was performed by two separate methods. First, as described in detail elsewhere,14 D and I alleles were amplified by the polymerase chain reaction with standard primers15 in a reaction mixture containing 5% DMSO; allele size was then determined on agarose gels. Putative DD genotypes were then confirmed by the triple-primer method.16
Statistics
The 
2 test was used to compare genotype frequency between groups. The Kruskal-Wallis test was used to compare continuous variables between groups, and the Kaplan-Meier method, using a log rank test, was employed for survival analysis (SPSS). The end points of the study were required renal replacement at the time of genotyping and the rate of deterioration of renal function as assessed by the slope of reciprocal creatinine.
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Results |
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A total of 822 patients were studied: 471 were male and 460 were on RRT at the time of study. The median age at presentation was 42 years (range, 8 to 82). The mean creatinine level at presentation was 131 µmol/L (range, 43 to 1620). The period of follow-up was the time to reach end-stage chronic renal failure or the time to censoring in patients who were not on RRT. The median follow-up period was 46 months (range, 0 to 252).
ACE Genotype
The genotype distribution in the patient group was 312 DD (38%), 366 ID (44.5%), and 144 II (17.5%). In the control group the genotype distribution was 93 DD (25.1%), 203 ID (54.7%), and 75 II (20.2%) (P<.05, 2). In patients who required RRT, the genotype distribution was DD 183, ID 206, and II 78 compared with respective values of 123, 151, and 64 in the group not requiring RRT (P=.62).
We then analyzed the patient data subdivided by genotype to determine whether genotype had any influence on the natural history of disease. There was a trend for patients who were II homozygotes to be older and to have a slightly higher BP at presentation than did patients who were DD homozygotes. The median age and age range (in years) at presentation were as follows: DD, 40 (8 to 79); ID, 43 (14 to 82); and II, 43 (12 to 75) years (P=.078). Presenting SBP values were as follows: DD, 138 (88 to 220); ID, 142 (90 to 210); and II, 142 (105 to 240) mm Hg (P=.048). Presenting DBP values were as follows: DD, 86 (60 to 150); ID, 87 (52 to 130); and II, 90 (60 to 110) mm Hg (P=.06). Presenting creatinine values (median and range) for DD, ID, and II genotypes were 120 (43 to 1586), 130 (53 to 1080), and 145 (43 to 1620) µmol/L, respectively (P=.165). No difference was observed in the number of antihypertensive medications, the level of protein excretion, or the age at which RRT was started. The follow-up period (in months) was similar for all three groups: DD, 40 (0 to 252); ID, 48 (0 to 184); and II, 49 (0 to 164), respectively (P=.1). However, progression to renal failure occurred faster in DD homozygotes, as assessed by the slope of the serum creatinine–versus-time plot: DD, -3.0 (-6.7, 5.0); ID, -2.01 (-16.6, 1.6); and II, -1.88 (-10.7, 7.7) (slopex10-6 [L/µmol·day], P=.015; Fig 1
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Comparison of renal survival data as a function of genotype revealed no overall difference. In view of the observed trend toward older age and higher BP in the II group (which may suggest later presentation in this group), we analyzed a subgroup of patients who had a presenting serum creatinine level <200 µmol/L (n=225). Within this group there was no difference in age, creatinine level, BP at presentation, or duration of follow-up. Renal survival analysis for this group of patients (86 DD, 106 ID, and 33 II) showed a significant difference in favor of those with the II genotype (Fig 2; P=.039). The proportions of patients requiring dialysis were 23% (DD), 26.4% (ID), and 6.1% (II) (P=.047).
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Additional subgroup analysis was performed by independently comparing the effect of ACE genotype on renal disease progression in patients with glomerular and those with tubulointerstitial diseases. Four hundred nineteen patients with glomerular diseases included those with IgA nephropathy (171), unspecified glomerulonephritis (87), membranous glomerulonephritis (82), focal and segmental glomerulosclerosis (15), diabetic nephropathy (39), and mesangiocapillary glomerulonephritis (25). The group with tubulointerstitial diseases included those with reflux nephropathy (130), adult polycystic kidney disease (102), and chronic tubulointerstitial nephritis (49). An effect of ACE genotype on disease progression was observed only in patients with glomerular diseases (P=.015; Table).
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Discussion |
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Ang II has a potentially important role in the development of glomerulosclerosis17 through its actions as a growth factor and regulator of cell growth and matrix production. Furthermore, inhibition of Ang II production attenuates progression of both diabetic and nondiabetic renal disease.18 19 Association studies of the ACE genotype in renal and cardiovascular disease, however, have yielded conflicting results. In the present study we have shown an increased frequency of the DD genotype in patients with renal disease; other studies have not. Similarly, previous studies have suggested that a higher proportion of patients on dialysis have the DD genotype20 ; other studies21 22 including ours have failed to confirm this finding. Part of the reason for these discrepancies lies in the fact that large numbers of subjects are needed for association studies to prevent spurious conclusions. Inclusion of patients with different forms of disease creates an inhomogeneous group, with the consequent risk of "diluting out" minor gene effects in one disease group by including "uninformative" patients. This is particularly true of renal disease, whose incidence is low. Although the present study is the largest series reported, it is still inadequate to assess the role of the ACE genotype in individual disease groups.
Second, the choice of control group is important. If ACE genotype is associated with death due to cardiovascular disease, then the D allele may be "depleted" in older patients or populations with a high incidence of cardiovascular disease. Thus, a higher proportion of DD homozygotes in patients with renal disease than in a control group of similar age is consistent with an effect of ACE genotype on the development of either renal disease or clinically relevant disease.9 In support of this suggestion that genotype might be associated with disease severity and thus bring patients to clinical attention, DD homozygotes experience a more rapid deterioration of renal function, as determined by the slope of the serum creatinine–versus-time plot. Moreover, when we studied patients who presented without advanced renal failure (creatinine <200 µmol/L), we found evidence of significantly improved renal survival in favor of the II genotype.
We also performed separate subgroup analyses in patients with glomerular diseases and those with tubular diseases, since some evidence indicates a difference in response to ACE inhibition between these two groups.19 23 An influence of ACE genotype on the rate of renal function deterioration was observed only in the group of patients with primary glomerular diseases. This finding may suggest a mechanism for the disparate results observed in treatment with ACE inhibitors and may indicate that the role of the RAS and Ang II on glomerular hemodynamics and cell function is most important.
Whether the I/D polymorphism represents a functional mutation in the ACE gene or is simply proximal to a functional mutation remains unresolved. Likewise, results of association studies may be interpreted as the ACE gene's simply being close to a "true" candidate gene for renal/cardiovascular disease progression. Our results, however, suggest that the I/D polymorphism of the ACE gene may be related to the development and rate of progression of glomerular disease. These results will require confirmation by larger, collaborative studies to establish the role and relative contribution of individual candidate genes. Finally, while large prospective studies serve as the "gold standard" for testing the role of candidate genes in disease,24 25 genetic effects in multifactorial disease may be too subtle to detect when "all-or-none" end points and measurements (such as the rate of disease development, independent of other risk factors) are evaluated. With relatively uncommon diseases, such as primary glomerular diseases, informative studies will be achieved only by multicenter collaboration.26
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Selected Abbreviations and Acronyms |
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Acknowledgments |
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We gratefully acknowledge the support of the National Kidney Research Fund and the British Heart Foundation.
Received June 8, 1996; first decision July 11, 1996; accepted August 21, 1996.
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References |
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