Contribution of genetic polymorphism in the renin-angiotensin system to the development of renal complications in insulin-dependent diabetes: Genetique de la Nephropathie Diabetique (GENEDIAB) study group

Angiotensin-1 converting enzyme polymorphisms in chronic beryllium disease

To test the hypothesis that the angiotensin converting enzyme (ACE) genotype is associated with chronic beryllium disease (CBD) and disease severity, we studied 50 cases of CBD and compared their ACE genotype to that of two different control groups, consisting of: (1) 50 participants from a beryllium machining facility; and (2) 50 participants from a non-beryllium-associated workplace. We found no statistically significant difference in the frequency of the I or D allele or of the DD genotype among cases of CBD and either control group. The odds ratio (OR) for the CBD DD genotype as compared with the non-DD genotype was 1.58 (95% confidence interval [CI]: 0.68 to 3.66, p = 0.12) for the beryllium-exposed control group, and 1.09 (95% CI: 0.48 to 2.46, p = 0.56) for the non-beryllium-exposed controls. We found an association between serum ACE activity and the ACE genotype, with DD cases having the highest median serum ACE activity (p = 0.005). We evaluated the beryllium lymphocyte proliferation test (BeLPT), bronchoalveolar lavage (BAL) cell components, chest radiography, pulmonary function test results, and exercise physiology in our CBD cases. No statistically significant associations with these disease markers were found for the CBD cases with the DD genotype. Although the difference was not statistically significant, the DD cases had a shorter median duration of exposure to beryllium before diagnosis of CBD, and tended to have a weaker response in their blood and BAL BeLPT than did the non-DD cases. These findings may indicate that the ACE genotype is important in the immune response to beryllium and in progression to beryllium disease.

Renal changes on hyperglycemia and angiotensin-converting enzyme in type 1 diabetes

Hyperglycemia causes capillary vasodilation and high glomerular capillary hydraulic pressure, which lead to glomerulosclerosis and hypertension in type 1 diabetic subjects. The insertion/deletion (I/D) polymorphism of the angiotensin I-converting enzyme (ACE) gene can modulate risk of nephropathy due to hyperglycemia, and the II genotype (producing low plasma ACE concentrations and probably reduced renal angiotensin II generation and kinin inactivation) may protect against diabetic nephropathy. We tested the possible interaction between ACE I/D polymorphism and uncontrolled type 1 diabetes by measuring glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) during normoglycemia ( approximately 5 mmol/L) and hyperglycemia ( approximately 15 mmol/L) in 9 normoalbuminuric, normotensive type 1 diabetic subjects with the II genotype and 18 matched controls with the ID or DD genotype. Baseline GFR (145+/-22 mL/min per 1.73 m2) and ERPF (636+/-69 mL/min per 1.73 m2) of II subjects declined by 8+/-10% and 10+/-9%, respectively, during hyperglycemia; whereas baseline GFR (138+/-16 mL/min per 1.73 m2) and ERPF (607+/-93 mL/min per 1.73 m2) increased by 4+/-7% and 6+/-11%, respectively, in ID and DD subjects (II versus ID or DD subjects: P=0.0007 and P=0.0005, for GFR and ERPF, respectively). The changes in renal hemodynamics of subjects carrying 1 or 2 D alleles were compatible, with a mainly preglomerular vasodilation induced by hyperglycemia, proportional to plasma ACE concentration (P=0.024); this was not observed in subjects with the II genotype. Thus, type 1 diabetic individuals with the II genotype are resistant to glomerular changes induced by hyperglycemia, providing a basis for their reduced risk of nephropathy.

Effect of ACE gene on diabetic nephropathy in NIDDM patients with insulin resistance

We investigated the influence of the angiotensin-converting enzyme (ACE) gene on the onset and/or progression of diabetic nephropathy in 62 Japanese patients with non-insulin-dependent diabetes mellitus (NIDDM; type II diabetes). Because a number of factors are believed to be involved in the onset and/or progression of diabetic nephropathy, especially in patients with NIDDM, we selected the patients with well-matched risk factors, duration of disease, glycemic control, blood pressure, and others. All patients had normal renal function and none were receiving ACE inhibitors. Patients were divided into three groups according to albumin excretion rate (AER): group A, patients with an AER less than 15 microg/min (n = 29); group B, patients with an AER between 15 and 70 microg/min (n = 19); and group C, patients with an AER greater than 70 microg/min (n = 14). The glucose disposal rate was estimated using a euglycemic hyperinsulinemic clamp. We determined the mean glucose disposal rate in 132 patients with NIDDM (6.49 mg/kg/min). Patients with a glucose disposal rate less than the mean rate were considered to have a high degree of insulin resistance (n = 36). The presence of an insertion/deletion (I/D) polymorphism of the ACE gene was determined by the polymerase chain reaction method. Among patients with a high degree of insulin resistance, diabetic nephropathy was present in 2 of 11 patients with the II genotype of the ACE gene compared with 19 of 25 patients with the ID or DD genotype (P = 0.0024). The prevalence of diabetic nephropathy was greater in patients with both significant insulin resistance and the D allele (19 of 25) than in the remaining patients (14 of 37; odds ratio, 5.20). These results suggest that the ACE gene influences the onset and/or progression of diabetic nephropathy in patients with NIDDM with significant insulin resistance.

M235T angiotensinogen gene polymorphism and cardiovascular renal risk

OBJECTIVE

In this meta-analysis, we attempted to derive pooled estimates for the putative associations between various cardiovascular-renal disorders and the M235T polymorphism of the angiotensinogen gene.

METHODS

Case-control studies were combined, using the Mantel and Haenszel approach. Joint P values for continuous variables were calculated by Stouffer's method. Continuous measurements reported in different units were expressed on a percentage scale using the intrastudy mean of the MM genotype as denominator.

RESULTS

The computerized database used for this analysis included 69 reports with an overall sample size of 27,906 subjects. Overall, possession of the T allele was associated with an increased risk of hypertension. In comparison with the MM reference group (number of studies, n = 32), the excess risk was 31% (P = 0.001) in TT homozygotes and 11% (P = 0.03) in TM heterozygotes. The sensitivity analysis showed that this association was present only in whites (T allelic frequency, f = 42.2%), but not in blacks (f = 77.0%) or Asians (f = 78.0%). Atherosclerotic complications (n = 12), renal microvascular disorders (n = 13), cardiomyopathy (n = 2) or diabetic retinopathy (n = 3) were not correlated with the M235T polymorphism. Publication bias was observed for hypertension, but not for coronary heart disease, including myocardial infarction, and for microvascular nephropathy. Furthermore, in comparison with the MM control group, the circulating angiotensinogen levels (n = 8) were raised by 11 and 7% (P = 0.01) in TT and TM subjects, respectively. In contrast, plasma levels of the angiotensin I converting enzyme (n = 4) and body mass index (n = 15) were not associated with the T allele.

CONCLUSION

The T allele encoding angiotensinogen is not associated with atherosclerotic or microvascular complications, but in Caucasians behaves as a marker for hypertension. This association, which may have been inflated by publication bias, does not necessarily imply causality.

Hyperglycemia and angiotensin-mediated control of the renal circulation in healthy humans

Type 1 and type 2 diabetics have an enhanced renal vasodilator response to angiotensin-converting enzyme (ACE) inhibition despite suppressed plasma renin activity (PRA), indicating possible activation of the intrarenal renin angiotensin system. To investigate the role of hyperglycemia, we evaluated the renal hemodynamic response to ACE inhibition in 9 healthy subjects in high-salt balance after steady-state hyperglycemia (8.4+/-1 mmol/L) was achieved via intravenous glucose administration. Renal plasma flow (RPF) and glomerular filtration rate (GFR) responses to captopril and to angiotensin II (Ang II) were measured as paraminohippuric acid and inulin clearances. Hyperglycemia produced a significant increase in RPF of 117 mL. min-1. 1.73 m-2 after 90 minutes but not GFR. Administration of captopril at a dose of 25 mg during glucose infusion led to an increase in RPF of 173+/-24 mL. min-1. 1.73 m-2 (P<0.01) but did not significantly change RPF in the absence of hyperglycemia (7+/-21 mL. min-1. 1.73 m-2). Captopril did not alter GFR in the presence or absence of hyperglycemia. Ang II infusion during hyperglycemia decreased RPF by 45+/-16 mL. min-1. 1. 73 m-2, and this was significantly enhanced by captopril (-98+/-26 mL. min-1. 1.73 m-2, P<0.05). In contrast, there was no enhancement of the vasoconstrictor response to Ang II in the absence of hyperglycemia. PRA did not change with hyperglycemia. Enhancement of renal vasodilation during hyperglycemia by captopril without alteration of PRA suggests activation of the intrarenal renin angiotensin system.

Angiotensinogen (M235T) and angiotensin-converting enzyme (I/D) polymorphisms in association with plasma renin and prorenin levels

OBJECTIVE

The angiotensinogen T235 allele is associated with elevated plasma angiotensinogen levels whereas the angiotensin-converting enzyme (ACE) deletion (D) allele is associated with elevated ACE activity. It remains unclear, however, whether these genetically mediated elevations of angiotensinogen and ACE levels are functionally relevant Given that the renin-angiotensin system is subject to renin feedback regulation, we specifically investigated the associations between the angiotensinogen T235 allele and the ACE D allele with plasma renin and prorenin levels.

DESIGN AND METHODS

Plasma levels of renin, prorenin, angiotensinogen, ACE and aldosterone, as well as angiotensinogen and ACE genotypes were determined in 228 men and 168 women (age 52-65 years), who had participated in a population survey in southern Germany. Subjects taking antihypertensive drugs or oestrogen replacement therapy were excluded.

RESULTS

We corroborated previous findings demonstrating associations between the T235M polymorphism and plasma angiotensinogen levels (P < 0.05) and between the ACE I/D polymorphism and plasma ACE (P < 0.01). After adjustment for sex, age and blood pressure, the T235 allele of the angiotensinogen gene was also related to lower plasma prorenin (P < 0.03) and renin (P < 0.01) levels, but not to plasma ACE and aldosterone. By contrast, the ACE I/D polymorphism was not related to components of the system other than plasma ACE.

CONCLUSIONS

The angiotensinogen T235 allele is associated with decreased renin levels. This finding may point to a mechanism that counteracts the genetic elevation of angiotensinogen plasma levels and, thus, the plasmatic angiotensin II-generating pathway in subjects carrying the angiotensinogen T235 allele. These results may help to explain discrepant findings regarding associations between this allele and cardiovascular disorders. Furthermore, the presumed feedback downregulation of renin levels supports the importance of angiotensinogen as a determinant of angiotensin II generation. Finally, no evidence was found suggesting that the ACE D allele affects components of the circulating renin-angiotensin system other than plasma ACE.

Genetic polymorphisms of the renin-angiotensin system and the outcome of focal segmental glomerulosclerosis in children

BACKGROUND

The clinical course of primary focal segmental glomerulosclerosis (FSGS) in children is variable, with some patients having a much more rapidly progressing course than others. The purpose of our study was to compare the frequency of three polymorphisms of the renin-angiotensin system (RAS) in children with FSGS with that in healthy controls of matching ethnic groups, and to determine whether the clinical outcome of FSGS was associated with different RAS genotypes.

METHODS

Three RAS genotypes were examined in 47 Jewish and Arab children with biopsy-proven primary FSGS and in a large control group: the ACE insertion/deletion polymorphism in intron 16, the M235T mutation in the angiotensinogen gene, and the A1166C in the angiotensin II type 1 receptor gene (AT1R).

RESULTS

Arab patients showed a greater tendency towards progressive renal disease than their Jewish counterparts (12 of 21 vs. 9 of 26, P = 0.05) and were less likely to achieve remission (3 of 21 vs. 11 of 26, P < 0.04), despite similar clinical presentation, medical management and follow-up. The RAS allele prevalence was similar among patients and controls of matching ethnic backgrounds, and no difference in allele frequency was found between Arabs and Jews. Homozygotes for the ACE insertion genotype (II) were significantly less likely to have progressive renal disease than patients with the other genotypes (ID and DD; 0 of 6 vs. 21 of 41; P < 0.022). The other RAS polymorphisms were not associated with variations in the clinical course of childhood FSGS.

CONCLUSIONS

Homozygosity for the ACE insertion allele may have a protective effect in children with FSGS and can serve as a positive prognostic indicator at diagnosis. The D allele may exert a detrimental dominant effect on outcome. Neither the ACE gene polymorphism nor the other RAS polymorphisms studied are associated with disease prevalence. The AT1R and angiotensinogen gene polymorphisms are not associated with progression of renal disease in FSGS. Ethnic differences in the clinical course of the disease are not linked to these polymorphisms.

Angiotensin II, nitric oxide, and end-organ damage in hypertension

The adaptive changes that accompany hypertension and involve the kidney, heart, and vessels, namely, muscle hypertrophy/hyperplasia, endothelial dysfunction and extracellular matrix increase can, in fact, be maladaptive and eventually lead to end-organ disease, such as renal failure, heart failure, and coronary disease. However, these changes vary markedly between individuals with similar levels of hypertension. Nitric oxide (NO), an endogenous vasodilator and inhibitor of vascular smooth muscle and mesangial cell growth, is synthesized in the endothelium by a constitutive NO synthase (NOS). NO antagonizes the effects of angiotensin II on vascular tone and growth and also down-regulates the synthesis of angiotensin converting enzyme (ACE) and angiotensin II type 1 (AT-1) receptors. In hypertension, the physiologic response to the increased shear stress and cyclic strain is to upregulate NOS activity in endothelial cells. Upregulation of vascular NOS activity is a homeostatic adaptation to the increased hemodynamic workload that may help in preventing end-organ damage. Indeed, hypertension-prone salt-sensitive rats manifest a decrease (instead of an increase) in vascular NOS activity when hypertensive; these rats develop severe vascular hypertrophy, left ventricular hypertrophy, and renal injury. Studies in hypertensive humans suggest that, independent of the effects of salt on blood pressure, salt sensitivity may be a marker for susceptibility to the development of endothelial dysfunction as well as cardiovascular and renal injury. We hypothesize that in hypertension, recognition of markers of cardiovascular susceptibility to injury and the understanding of the pathophysiological mechanisms involved may open new opportunities for therapeutic intervention. In this context, only those antihypertensive agents that lower blood pressure and concomitantly restore the homeostatic balance of vasoactive agents such as angiotensin II and NO within the vessel wall would be effective in preventing or arresting end-organ disease.

Deletion polymorphism of the angiotensin converting enzyme gene predicts persistent proteinuria in Henoch-Schönlein purpura nephritis

OBJECTIVE

To study the influence of deletion/insertion polymorphism in the 16th intron of the angiotensin converting enzyme (ACE) gene on clinical manifestations of Henoch-Schönlein purpura nephritis.

STUDY DESIGN

Cross sectional study. ACE gene polymorphism was determined in patients (4-15 years old at onset) with Henoch-Schönlein purpura nephritis (n = 40) and compared with that in patients with IgA nephropathy (n = 79).

MAIN OUTCOME MEASURES

ACE genotypes, systemic blood pressures, urine protein excretion rate, haematuria, creatinine clearance, serum ACE activities.

RESULTS

The initial clinical manifestations of both Henoch-Schönlein purpura nephritis and IgA nephropathy were no different among homozygotes for insertion (II) and deletion (DD), and heterozygotes (ID) for the ACE gene. In patients with Henoch-Schönlein purpura nephritis, the incidence of moderate to heavy proteinuria at four and eight years after onset was more than five times higher in the DD genotype than in the II or ID genotypes. No such trend was seen in patients with IgA nephropathy. The number of patients with Henoch-Schönlein purpura nephritis in whom proteinuria resolved at four and eight years after onset was significantly lower in the DD genotype compared with the II genotype, whereas no differences were detected among the three different genotypes in patients with IgA nephropathy. Plasma ACE activities in patients with the DD genotype were significantly higher than in those with non-DD genotypes.

CONCLUSIONS

The ACE DD genotype predicts persistent proteinuria in Henoch-Schönlein purpura nephritis. The proteinuria might be related to a defective angiotensin system which is genetically determined by the D/I polymorphism.

Polymorphisms of angiotensin converting enzyme and plasminogen activator inhibitor-1 genes in diabetes and macroangiopathy1

BACKGROUND

An insertion or deletion (I/D) polymorphism in the angiotensin converting enzyme (ACE) gene and a 4/5-guanine tract polymorphism (4G/5G) in the promoter region of the plasminogen activator inhibitor-1 (PAI-1) gene are associated with the plasma activities of these substances and with coronary heart disease. In smooth muscle cells and mesangial cells, the angiotensin II synthesized by ACE increases mRNA expression and the activity of PAI-1, which promotes antifibrinolysis and the accumulation of extracellular matrix. Therefore, ACE and PAI-1 polymorphisms may have a synergistic effect on diabetic nephropathy and macroangiopathy.

METHODS

Using multivariate logistic regression analyses, we investigated the independent or synergistic effects of the ACE I/D and PAI-1 4G/5G polymorphisms on the development of diabetic nephropathy and macroangiopathy in 208 patients with non-insulin dependent diabetes mellitus (NIDDM) over a 15 year period.

RESULTS

Advanced diabetic nephropathy, defined as impaired renal function and diabetic retinopathy, was present in 98 patients. Manifest macrovascular diseases, confirmed by both clinical signs and physical and laboratory examinations, were present in 56 patients. There was no significant difference in the genotype distribution of ACE or PAI-1 polymorphisms between subjects with advanced nephropathy and those with normal renal function. There was no significant difference in the renal survival rate between patients with differing ACE or PAI-1 genotypes. Subjects with macroangiopathy had a higher frequency of the DD genotype than those without macroangiopathy. Subjects with both DD and 4G4G genotypes had a higher incidence of macroangiopathy than those with any other pair of genotypes. Multivariate logistic regression analysis showed that there was no association between ACE or PAI-1 polymorphisms and diabetic nephropathy. The ACE DD genotype and its interaction with the PAI-1 4G4G genotype and the presence of advanced diabetic nephropathy were positively associated with macrovascular disease.

CONCLUSION

These results indicate that the ACE DD genotype and its interaction with the PAI-1 4G4G genotype are independent risk factors for macroangiopathy, but not for the progression of diabetic nephropathy in NIDDM patients, and that the genotyping of PAI-1 and ACE polymorphisms, especially in patients with advanced diabetic nephropathy, may be useful for predicting and preventing macroangiopathy-related events.

Renal angiotensin converting enzyme promotes renal damage during ureteral obstruction

PURPOSE

We and others have shown that angiotensin II has a pivotal role in renal damage in various renal injuries. Although most angiotensin II actions are associated with the angiotensin type 1 receptor, there is increasing evidence that the angiotensin type 2 receptor also transduces some important effects of angiotensin II. In this regard we recently observed that mice with genetically engineered disruption of the angiotensin type 2 receptor, termed Agtr2 mutants, are more susceptible to structural renal damage after ureteral obstruction. Recent evidence suggests that a genetically determined increase in angiotensin converting enzyme activity in humans promotes end organ damage. Therefore, we determined whether renal damage in Agtr2 mutants is associated with heightened angiotensin converting enzyme activity.

MATERIALS AND METHODS

We studied 28 wild type and 19 Agtr2 mutant mice with unilateral ureteral obstruction. Seven days after obstruction was created serum samples were obtained to evaluate angiotensin converting enzyme activity. The obstructed and contralateral kidneys were harvested for histological analysis and determination of renal angiotensin converting enzyme activity by high pressure liquid chromatography.

RESULTS

Renal angiotensin converting enzyme was uniformly higher than serum angiotensin converting enzyme in normal wild type and Agtr2 mutant mice. However, even at baseline Agtr2 mutant mice had strikingly higher renal angiotensin converting enzyme activity than normal wild type mice (mean plus or minus standard error 1,492+/-83 versus 450+/-60 milliunits per gm. tissue weight, p <0.0005). Histological analysis revealed more extensive parenchymal damage in the obstructed kidneys of mutant mice than in identically treated controls. Notably while unilateral ureteral obstruction decreased renal angiotensin converting enzyme activity in each group, activity remained persistently higher in the Agtr2 mutants than in normal mice (mean 742+/-146 versus 310+/-43 milliunits per gm. tissue weight, p <0.005).

CONCLUSIONS

We propose that elevated renal angiotensin converting enzyme activity contributes to more severe renal parenchymal damage in ureteral obstruction by promoting the availability of growth factors, such as angiotensin II, or depleting antiproliferation factors, such as bradykinin or nitric oxide. These findings complement previous observations that angiotensin converting enzyme inhibition preserves the renal parenchyma after injury, including obstruction.

Pathogenesis, prevention, and treatment of diabetic nephropathy

It is likely that the pathophysiology of diabetic nephropathy involves an interaction of metabolic and haemodynamic factors. Relevant metabolic factors include glucose-dependent pathways such as advanced glycation, increased formation of polyols, and activation of the enzyme, protein kinase C. Specific inhibitors of the various pathways are now available, enabling investigation of the role of these processes in the pathogenesis of diabetic nephropathy and potentially to provide new therapeutic approaches for the prevention and treatment of diabetic nephropathy. Haemodynamic factors to consider include systemic hypertension, intraglomerular hypertension, and the role of vasoactive hormones, such as angiotensin II. The mainstay of therapy remains attaining optimum glycaemic control. Antihypertensive therapy has a major role in slowing the progression of diabetic nephropathy. Agents that interrupt the renin-angiotensin system such as angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists may be particularly useful as renoprotective agents in both the hypertensive and normotensive context.

Angiotensin converting enzyme gene polymorphisms and renal disease

In the past year there has been a profusion of reports identifying a possible association between the insertion/deletion polymorphism of the angiotensin converting enzyme and renal diseases. Rather than clarifying the situation, it has become more difficult to interpret its significance owing to small sample sizes and concerns over methodology; hence, studies are frequently contradictory. Despite these concerns there is evidence for a role of this polymorphism in progressive renal disease. This review summarizes the major studies in this field and suggests future strategies that might be employed to identify useful genetic markers in nephrology, for which the angiotensin converting enzyme polymorphism has acted as an important paradigm.

Diabetic nephropathy is associated with AGT polymorphism T235: results of a family-based study

Diabetic nephropathy is a serious and frequent complication of insulin-dependent diabetes mellitus (IDDM) that has a strong genetic component. Several case-control studies have reported conflicting results with regard to the role of angiotensinogen gene polymorphisms, specifically the M235T T allele, in the development of diabetic nephropathy. The primary limitation of the case-control approach is that bias may be introduced by unrecognized differences in the populations selected for cases and control subjects. In contrast, family-based approaches, such as the transmission/disequilibrium test, assess whether a particular variant, or allele, is transmitted preferentially from a parent having a single copy of that allele. Thus each family provides its own control, thereby eliminating spurious results caused by mismatched population samples. To take advantage of this study design for further investigation of M235T, we collected from the Joslin Diabetes Center in Boston 148 IDDM patients with diabetic nephropathy, 62 nephropathy-free patients with long-duration IDDM, and, very importantly, parents of all these individuals. We found that among males (but not females) the T allele of the M235T polymorphism was transmitted preferentially to those with nephropathy compared with IDDM patients without nephropathy (P=.05). Moreover, the T allele was transmitted preferentially to patients with the most severe manifestation of nephropathy, end-stage renal disease (P=.04). In conclusion, results obtained in our family-based study support a role of the angiotensinogen gene M235T polymorphism, and specifically the T allele, in the development of diabetic nephropathy in IDDM.

Nitric oxide in hypertension: relationship with renal injury and left ventricular hypertrophy

Hypertension is accompanied by architectural changes in the kidney, heart, and vessels that are often maladaptive and can eventually contribute to end-organ disease such as renal failure, heart failure, and coronary disease. Nitric oxide, an endogenous vasodilator and antithrombotic agent synthesized in the endothelium by a constitutive nitric oxide synthase, inhibits growth-related responses to injury in vascular cells. Specifically, in the presence of hypertension, nitric oxide may work in the kidney by inhibiting both mesangial cell hypertrophy and hyperplasia as well as synthesis of extracellular matrix and in the heart and systemic vessels by modulating smooth muscle cell hypertrophy and hyperplasia. The effects of nitric oxide are antagonistic of the effects of angiotensin II. Shear stress and cyclic strain, physical forces known to operate in hypertension, are accompanied by increases in endothelial nitric oxide synthase expression, nitric oxide synthase protein, and nitric oxide synthase activity in endothelial cells. Experimental studies using genetic models of hypertension show a variation in hypertension-modulated vascular nitric oxide synthase activity in different strains of rats. These studies suggest that upregulation of vascular nitric oxide synthase activity is a homeostatic adaptation to increased hemodynamic workload in hypertension and that this may help prevent end-organ damage. If these findings apply to humans, differences in end-organ disease seen in patients with similar degrees of hypertension may be due in part to genetic differences in vascular nitric oxide synthase activity in response to hypertension.

The deletion/insertion polymorphism of the angiotensin converting enzyme gene and cardiovascular-renal risk

OBJECTIVE

This meta-analysis attempted to derive pooled estimates for the associations between various cardiovascular-renal disorders and the deletion/insertion (D/I) polymorphism of the angiotensin converting enzyme (ACE) gene.

METHODS

Case-control studies were combined, using the Mantel-Haenszel approach. Joint P values for continuous variables were calculated by Stouffer's method. Continuous measurements reported in different units were expressed on a percentage scale using the within-study mean of the II genotype as the denominator.

RESULTS

The computerized database used for this analysis included 145 reports with an overall sample size of 49 959 subjects. Overall, possession of the D allele was associated with an increased risk of atherosclerotic and renal microvascular complications. In comparison with the II reference group, the excess risk in DD homozygotes (P < 0.001) was 32% for coronary heart disease (CHD; 30 studies), 45% for myocardial infarction (20 studies), 94% for stroke (five studies) and 56% for diabetic nephropathy (11 studies). The corresponding risk in DI heterozygotes amounted to 11% (P= 0.02), 13% (P= 0.02), 22% (P= 0.10) and 40% (P < 0.001), respectively. Hypertension (23 studies), left ventricular hypertrophy (five studies), hypertrophic or dilated cardiomyopathy (eight studies) and diabetic retinopathy (two studies) were not related to the DI polymorphism. Publication bias was observed for CHD, myocardial infarction and microvascular nephropathy, but not hypertension. In studies with DNA amplification in the presence of insertion-specific primers, the risk associated with the DD genotype increased to 150% [95% confidence interval (CI) 76-256; four studies] for diabetic nephropathy, but decreased to 12% (95% CI -3 to 28; seven studies) for CHD and 14% (95% CI -6 to 37; four studies) for myocardial infarction. On the other hand, the pooled odds ratios did not materially change if the meta-analysis was limited to articles published in journals with an impact factor of at least 4. Furthermore, compared with the II control group, the circulating ACE levels (29 studies) were raised 58 and 31% (P < 0.001) in DD and DI subjects, respectively. In contrast, plasma renin (10 studies), systolic and diastolic blood pressure (46 studies) and body mass index (30 studies) were not associated with the D allele.

CONCLUSION

The D allele is not associated with hypertension, but behaves as a marker of atherosclerotic cardiovascular complications and diabetic nephropathy. These associations do not necessarily imply a causal relationship and may have been inflated by publication bias. Nevertheless, their possible therapeutic implications may be subject to further investigation in prospective (intervention) studies.