(Circulation. 1996;93:1630-1633.)
© 1996 American Heart Association, Inc.
Articles |
From the Department of Internal Medicine, Awaji-Hokudan Public Clinic (K.K.), Hyogo, Japan; Hyogo (Japan) Prefectural Awaji Hospital (K.K., T.M.); and the Department of Pathology (N.K., K. Saito), Department of Community and Family Medicine (N.N.), and Department of Cardiology (K. Shimada), Jichi Medical School, Tochigi, Japan.
Correspondence to Dr Kazuomi Kario, 480, Ikuha, Hokudan, Tsuna, Hyogo, 656-16, Japan.
| Abstract |
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Methods and Results To study the association between the ACE I/D polymorphism and hypertensive cerebrovascular disease, we identified the ACE I/D genotype in 228 hypertensive and 104 normotensive Japanese subjects. Compared with its frequency (0.31) in the 90 hypertensives without lacunae detected by magnetic resonance imaging, the ACE*D allele frequency was significantly higher (0.47; P<.001) in the 138 hypertensives with silent or clinically overt ischemic stroke, whereas there was no significant difference between its frequency in hypertensives without lacunae and in 104 normotensive control subjects (0.34). The positive association between the ACE I/D genotype and ischemic stroke in hypertensive patients was independent of other risk factors.
Conclusions We found a positive association between the ACE*D allele and ischemic stroke in Japanese hypertensives in our study. The ACE*D allele may be an independent risk factor for the development of cerebrovascular disease in hypertensive patients.
Key Words: cerebrovascular disorders enzymes genes hypertension
| Introduction |
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Genes that influence the renin-angiotensin system are potentially etiologic candidates for causing cardiovascular disease because their products exert a profound systemic effect on vasoconstriction and ACE inhibitors reduce the risk of cardiovascular disease. This supposition is supported by recent reports that the ACE I/D polymorphism is associated with increased risk for myocardial infarction in whites1 2 and Japanese.3 However, there have been no reports on the association of this polymorphism and stroke. There are some racial differences in the demographics of cardiovascular diseases. In Japan, stroke (especially that which occurs in preexisting hypertension) is more common and coronary artery disease much less common than in western countries.4 We propose that the ACE I/D polymorphism might be associated with hypertensive cerebrovascular disease in Japanese.
| Methods |
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40 years of age) who
attended an annual health examination. The subjects all resided in the
same district (Awaji-Hokudan), and they did not include any
first-degree relatives. Ischemic stroke was diagnosed when neurological deficits were accompanied by corresponding abnormal findings depicted by brain CT, MRI, and/or magnetic resonance angiography and was classified on the basis of the clinical categories established by the National Institute of Neurological Disorders and Stroke,5 as described practically by Takano et al.6
Brain MRI
Brain MRI was performed with a superconducting magnet with a
main field strength of 1.5 T (Toshiba MRT 200 FXII). The brain was
imaged in the axial plane in 8-mm-thick slices. T1-weighted images
were obtained by use of a short spin-echo pulse sequence with a
repetition time of 500 ms and an echo time of 13 ms. T2-weighted images
were obtained by use of a long spin-echo pulse sequence with a
repetition time of 4000 ms and echo times of 60 and 112 ms. The matrix
was 256x224 pixels. The images were evaluated for the number and
location of lacunae. Lacunae were strictly defined as lowsignal
intensity areas (<1 cm) on T1-weighted images, which were visible as
hyperintense lesions on T2-weighted images as illustrated
previously.7 Lacunae as defined above might include
lesions other than true infarcts such as état criblé,
especially if their size were small (ie, <5 mm).7 All of
the MRI images were interpreted in a blind fashion.
Detection of ACE I/D Polymorphism
We extracted genomic DNA from citrated whole blood using
salt/chloroform by a modification of a previously described
method.8 Enzymatic amplification of DNA was performed by
PCR with 0.1 µg of DNA extract and thermostable Taq
polymerase (Takara Biochemical) according to the manufacturer's
instructions.9 10 The PCR was performed in a thermal
reactor (MJ Research). The oligonucleotide sequences of
the PCR primers were 5'-CTGCAGACCACTCCCATCCTTTCT-3' and
5'-GATGTGGCCATCACATTCGTCAGAT-3'.11 The DNA was amplified
for 35 cycles with denaturation at 94°C for 30 seconds, annealing at
60°C for 30 seconds, and extension at 70°C for 60 seconds. The PCR
products were separated by electrophoresis on 3% agarose gel
(NuSieve 3:1 agarose gel, FMC Bioproducts) in 45 mmol/L
tris-borate and 1 mmol/L EDTA (pH 7.7) containing 0.5 mg/mL
ethidium bromide and were visualized by use of UV light.
Identification of the ACE genotype of all samples was made in a blind manner by the same investigator (N.K., who is a professional in identification of the ACE genotype).
Statistical Analysis
Statistical analysis was performed with the Statistical
Analysis System (version 6.03; SAS Institute, Inc). Allele
frequencies in different groups were compared by use of gene counting
and
2 analysis. After one-way ANOVA,
Scheffé's F test was used for comparison between the mean values
for the two groups. In the multivariate logistic
regression analysis in 228 hypertensive patients,
ischemic stroke (silent or clinically overt stroke) was the
dependent variable and the independent variables were age (by
10-year groups), sex (1=male, 2=female), smoking status (1=nonsmoker,
2=current or ex-smoker), ECG-LVH (1=absent, 2=present), family
history of known stroke or sudden death (1=absent, 2=present),
metabolic variables (hematocrit, total
cholesterol level, HDL-cholesterol level, and
glucose level, based on a 1 SD difference of each variable in the
total group of hypertensive patients), and ACE
genotype (1=II; 2=ID+DD). The
association between differences with a probability value less than .05
was considered significant.
| Results |
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The clinical and metabolic characteristics of the subjects
studied are shown in Table 1
. There were no significant
differences among the three groups in prevalence of current or
ex-smokers, those with family history of known stroke or sudden
death, or any metabolic variable. In 228 hypertensive
patients, male sex and ECG-LVH were more common in the stroke group
than in the nonstroke group (P<.05).
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The ACE genotype distributions of the hypertensive
stroke group were significantly different not only from those in the
normotensive control group but also from those in the hypertensive
nonstroke group (Table 2
), whereas there was no
significant difference between those in the hypertensive nonstroke
group and the normotensive control group. Compared with its frequency
(0.31) in the nonstroke group, the ACE*D allele
frequency was significantly higher in the stroke group (0.47;
P<.001), whereas there was no significant difference
between frequency of this allele in the nonstroke group and the
normotensive control group (0.34). There was no significant difference
in frequency of the ACE*D allele between the clinically
overt stroke group (0.50) and the silent stroke group (0.44), and both
were significantly higher than in the nonstroke group
(P<.05).
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In all 332 subjects studied (the 104 normotensive control subjects and
228 hypertensives), a significant increase in the prevalence of
clinically overt ischemic stroke was found across the three
ACE genotypes, with higher values associated with
the ACE*D allele (41% in those with the DD
genotype, 27% in those with the ID
genotype, and 16% in those with the II
genotype;
2=12.1, P<.005).
The ACE genotype distribution of the subjects with a
family history of known stroke or sudden death (II=21
[30%], ID=31 [45%], DD=17 [25%]) was
also significantly different from that of those without such family
history (103 [39%], 127 [48%], and 33 [13%], respectively;
2=6.55, P<.05). Frequency of the
ACE*D allele was also significantly higher in the former
group than in the latter (0.46 versus 0.37;
2=4.99, P<.05). In the association
study between the ACE genotype and risk factors
listed in Table 1
, no risk factor except family history was associated
with the ACE genotype.
In the multivariate logistic regression
analysis of hypertensive patients (Table 3
),
ischemic stroke (silent or clinically overt) was independently
associated with ACE genotype (OR=2.44,
P<.005) and age (OR=1.61, P<.01).
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| Discussion |
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Frequency of the ACE*D allele was significantly higher in the hypertensive stroke group than in the hypertensive nonstroke group or in the group of normotensive control subjects. The ACE I/D polymorphism is responsible in part for the interindividual variation in plasma ACE levels, such that subjects with the DD genotype have approximately twice the plasma levels of ACE compared with those with the II genotype.12 The ACE I/D polymorphism identifies genetic variants that may contribute to the risk of ischemic stroke through increased vasoconstriction, cellular hypertrophy, and thrombosis after an increase in angiotensinogen II levels and the inactivation of bradykinin.13 These possibilities are supported by the clinical and experimental observations that after the administration of an ACE inhibitor, cerebral blood flow is well maintained and a downward shift in the limits of autoregulation may occur.14 Increased levels of immunoreactive angiotensin II, angiotensin II binding sites, and ACE in the cerebrospinal fluid have been reported in the spontaneously hypertensive rat.15 Thus, the role of the renin-angiotensin system in the brain might be greater in hypertensives than in normotensives.
Overall, a significant increase in the prevalence of clinically overt ischemic stroke and family history of known stroke or sudden death was found across the three ACE genotypes, with higher values associated with the ACE*D allele. These results also support the concept of a close association of the ACE I/D polymorphism with hypertensive cerebrovascular disease.
Previously, the ACE gene polymorphism was reported to be
unrelated to essential hypertension in whites,1 2 16 17 18
although at least one report did not support this.19 This
discrepancy also was found in studies of Japanese.20 21
However, no thorough evaluation of hypertensive target organ damage has
been performed. Indeed, in the present study as well, the
distribution of ACE genotypes and the frequency
(0.36) of the D allele in the entire group of
asymptomatic hypertensives combined with nonstroke and
silent stroke groups were no different from those in the normotensive
control group. We evaluated silent cerebrovascular disease by MRI,
which is the most sensitive method for detection of hypertensive
cerebrovascular damage,7 and we found that frequency of
the ACE*D allele was significantly higher in the silent
stroke group than in the nonstroke group (0.44 versus 0.31;
2=5.10, P<.05). The absence of any
difference in frequency of the ACE*D allele between the
silent stroke group and the clinically overt stroke group indicates the
important contribution of the renin-angiotensin system
to the pathogenesis of lacunae formation, even in the clinically silent
stage.
Frequencies of the ACE*D allele in the asymptomatic hypertensive (0.36) and normotensive control groups (0.34) were lower than those reported previously for westerners and for Japanese populations (0.4 to 0.6).1 2 3 11 17 18 19 20 Since our normotensive control group consisted of healthy participants in annual health examinations, the lower frequency of the ACE*D allele is probably characteristic of our district.
In conclusion, we found a positive association between the ACE*D allele and ischemic stroke in our study of Japanese hypertensives. This association was independent of other risk factors, including ECG-LVH. Thus, the ACE*D allele may be an independent risk factor for the development of cerebrovascular disease in hypertensive patients. The consistency of our results in different racial populations and their pathological relevance still need to be assessed by larger prospective association studies or linkage-based family studies.
| Selected Abbreviations and Acronyms |
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| Acknowledgments |
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Received December 4, 1995; revision received February 14, 1996; accepted February 16, 1996.
| References |
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Thr variant on blood pressure and other
cardiovascular risk factors in two Japanese
populations. J Hypertens. 1995;13:717-722. [Medline]
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