(Circulation. 2000;101:2060.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Department of Geriatric Medicine, Osaka University Medical School (J.H., T.K., N.S., K.I., T.O.), and the Department of Preventive Medicine, National Cardiovascular Center (S.B., T.M., J.O.), Suita, Osaka, Japan.
Correspondence to Jitsuo Higaki, MD, PhD, Department of Geriatric Medicine, Osaka University Medical School, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan. E-mail tkatsuya{at}yo.rim.or.jp
| Abstract |
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Methods and ResultsUsing a large number of Japanese subjects (n=5014) that were randomly selected from the general population (the Suita Study), we examined the association between ACE DD and hypertension. The frequency of DD (17.1%) in hypertensive men was significantly higher (P<0.0015) than that (11.8%) in other mildly hypertensive or normotensive men, and the estimated odds prevalence for hypertension (DD vs II) was 1.75 (95% CI 1.21 to 2.53). In contrast, no significant association was confirmed in women (OR 1.17, 95% CI 0.79 to 1.72).
ConclusionsDespite the lower frequency of the DD genotype in Japanese than in whites, the ACE gene polymorphism was associated with increased risk for hypertension, suggesting that this polymorphism is a mild but certain genetic risk factor for essential hypertension in men.
Key Words: renin angiotensin genetics population
| Introduction |
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Two recent studies describe a linkage between the ACE locus and hypertension in a large number of hypertensive sibs.8 9 An insertion/deletion (I/D) polymorphism in intron 16 of ACE was significantly associated with hypertension only in men. The ACE I/D polymorphism, identified in 1990 by Rigat et al,10 is partially associated with the plasma ACE level.11 Although the ACE DD genotype increases the plasma ACE concentration and the risk for numerous cardiovascular-renal diseased states, such as myocardial infarction,12 cardiomyopathy,13 IgA nephropathy,14 and diabetic nephropathy,15 the findings from case-control studies have not been consistently positive. Genetic and environmental heterogeneity among different ethnic groups may account for the inconsistent results.16 If so, the effect of gene polymorphism should be examined within a large homogeneous population.17
The present study examines the association between hypertension and ACE I/D polymorphism as well as sex specificity in the Japanese population. This study is the first large-scale genetic epidemiologic investigation to assess the cardiovascular risk of the ACE DD genotype in Japan.
| Methods |
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Measurements
Basic clinical variables included age, BMI, smoking and
drinking habits, alcohol consumption (mL/d), TC, TG, HDL-C, FPG,
creatinine, antihypertensive therapy, and the presence of
diabetes mellitus and IHD. After >10 minutes of rest, SBP and DBP were
measured twice by a single physician. Hypertension was defined as a
mean SBP of
160 mm Hg or a mean DBP of
95 mm Hg or
currently under antihypertensive medication. Height and weight were
also measured, and BMI was calculated by dividing weight in kilograms
by height in meters squared.
Determination of Genotype
DNA was extracted from 200 µL of buffy coat separated from
fresh blood with the use of a QIAamp Kit (QIAGEN). Template genomic DNA
(100 ng) was amplified by polymerase chain reaction with a thermal
cycler (Omni Gene; Hybaid). I/D polymorphism was
determined by agarose gel electrophoresis with ethidium bromide
staining, and DD genotype was reconfirmed by
insertion allelespecific amplification according to the
Lindpaintners protocol19 with a minor
modification.
Statistical Analysis
All statistical analyses were conducted with the use of
StatView 4.5J (Abacus Concepts) and JMP 3.0 (SAS). The difference in
genotype or allele distribution between hypertensive
subjects and other subjects was examined by
2
analysis. The association between ACE I/D
polymorphism and clinical variables was examined by the 1-way
ANOVA. We assessed the quantitative effects of covariates by multiple
logistic regression analysis by using JMP. Since the
inheritance manner of the D allele has not been
clarified, we examined its effect separately as follows: recessive
(DD vs ID+II), additive (DD
vs ID vs II), or dominant
(DD+ID vs II).
| Results |
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Genotype Distribution of ACE I/D
Polymorphism
ACE genotype distribution was significantly
deviated from Hardy-Weinbergs expectation in women
(
2=8.4, P<0.004) but not in total
or in men (
2=0.22, P=0.58).
Although the ACE DD genotype frequency was similar
between Japanese men and women (P=0.96), the frequency of
the I allele and that of the II
genotype were significantly higher in women than in men
(P<0.04). The significant difference of ACE
genotype distribution (
2=9.9,
P<0.008) between men and women was observed in
Japanese.
Sex Specificity in Association With Hypertension
Both genotype and allele distribution of the ACE
I/D polymorphism were significantly different between
hypertensive subjects and other subjects (Table 2
). The estimated odds ratio for
hypertension in individuals with the D allele was 1.15
(95% CI 1.05 to 1.27). To examine the sex-specific association with
hypertension, we compared genotype and allele distribution
separately among men and women. The results showed that in men but not
in women, ACE DD was significantly associated with
hypertension (Table 2
). The mean SBP in all of the tested men
was significantly associated with the ACE genotype,
whereas DBP was not. The association between major classic risk factors
and the ACE genotype was not significant among the
total number of tested women (Table 3
).
Multiple logistic regression analysis revealed that the
ACE DD genotype is an independent risk for essential
hypertension. The test of the effect of confounding factors for
hypertension revealed that the effect of ACE DD is mild but
significant in men (Table 4
). After full
adjustment for confounding factors (age, BMI, alcohol consumption,
smoking habit, TC, TG, HDL-C, creatinine, FPG, presence of
ischemic heart disease [IHD], and presence of diabetes
mellitus), the estimated odds ratio of DD (vs II)
was 1.75 (95% CI 1.21 to 2.53). When hypertension was defined through
the use of only DBP >95 mm Hg, the fully adjusted odds ratio of
DD (vs II) was 1.71 (95% CI 1.17 to 2.47). In
the estimation of the risk for systolic hypertension defined as
DBP <95 mm Hg and SBP >160 mm Hg, the fully adjusted odds
ratio was increased to 2.77 (1.09 to 6.54). On the other hand, the
effect of the ID genotype did not reach a
significant level in the increase of hypertension risk, suggesting that
the effect of the D allele is recessive. No association
was identified between the ACE genotype and
hypertension in women (Tables 2
and 3
and Figure 1
).
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Age Dependence in Association With Hypertension
To examine the age dependence in the association between ACE
DD and hypertension, we compared the effect of ACE DD
for hypertension in young and elderly subjects (Figure 2
). Subjects
60 years old were
categorized as "young"; subjects >60 years old were categorized as
"elderly." The highest percentage of ACE DD was observed
in elderly men, but the significance in the difference between
hypertensive subjects and others was similar between young and elderly
subjects (Figure 2a
). Although the prevalence of hypertension
increases along with age, the difference between young and elderly
subjects in men is bigger than that in women. In the subjects with
DD genotype, the incidence of hypertension in young
men (25%) was significantly higher (
2=7.2,
P=0.008) than that in young women (13%) (Figure 2b
).
In elderly subjects, however, the incidence of hypertension in men is
similar to that in women (
2=0.2,
P=0.63). The estimation of fully adjusted odds ratios for
hypertension in 4 groups indicates that the effect of ACE DD
is strong in young men but weak in elderly women (Figure 2c
).
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Association Between Presence of IHD and ACE
DD
On the other hand, the prevalence (%) of IHD tended to increase
among individuals with the DD genotype (Table 3
). The fully adjusted odds ratio (DD vs
ID+II) for IHD was 1.56 (0.96 to 2.58) in men and
1.80 (0.96 to 3.19) in women. In the whole population, the significant
association was observed between the presence of IHD and DD,
and the fully adjusted odds ratio (DD vs
ID+II) was 1.62 (1.08 to 2.36).
| Discussion |
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We determined the ACE genotype of >5000
individuals. One advantage of this investigation is that the
participants were randomly selected urban residents. The selection bias
of cases and control subjects has been avoided because our population
was simply divided into 2 groups according to the criteria for
hypertension. Since the proportion of ACE genotype
in the mildly hypertensive subjects (140 mm Hg
SBP
<160 mm Hg or 90 mm Hg
DBP <95 mm Hg) is
similar to that of the normotensive subjects (SBP <140 mm Hg and
DBP <90 mm Hg), we examined the relation between hypertensive
subjects and others. Another advantage is that the participants are all
Japanese. The D allele frequency among Japanese (35.5%)
was significantly lower than that in whites (51.1%) estimated by the
Copenhagen City Heart Study16
(
2=625.1, P<0.0001). Despite the
smaller prevalence of the DD genotype among Japanese
(13.1%) compared with whites (26.2%), the significance of the
male-specific association between hypertension and ACE DD
genotype is higher in the Suita Study than in the Framingham
Study.8 Though many confounding factors were
different between hypertensive subjects and other subjects, the
significant independent association of ACE DD with
hypertension remained after these factors were adjusted. The
DD but not the ID genotype was associated
with a significant increase in relative risk for hypertension compared
with the II genotype. This finding suggested that
the hypertensive effect of the D allele appeared with
recessive inheritance. Similar results were obtained from two different
races, suggesting that the ACE DD polymorphism or an
unknown linked gene has a mild but certain effect in the pathogenesis
of essential hypertension.
The female ACE genotype distribution was not confirmed to Hardy-Weinbergs law in this study. One possible reason for the excess of DD is that ACE DD associates with longevity,21 but ACE genotype proportion in senior subjects (>70 years of age) was not different from that in young or middle-aged subjects (data not shown). In our preliminary result, the basic genotype distributions of other genes were not different between men and women, suggesting that this observation is specific for the ACE gene.
On the other hand, it is notable that sex specificity in the
association between ACE DD and hypertension was confirmed in
this Japanese population. The mechanism of the sex specificity of
association with hypertension remains unclear. One notion is that
estrogen protects against hypertension, although ODonnell et
al8 could not detect a relation with estrogen
replacement therapy or menopause status. Our results suggested that the
sex specificity decreased in elderly subjects and increased in young
subjects (Figure 2b
). The fact that estrogen replacement therapy
is uncommon in Japanese (<1% of Japanese women undergo this therapy)
also supports our hypothesis.
A minor difference from the Framingham Study is that ACE DD
was associated with SBP but not DBP. Since SBP reflects the increased
cardiac output or resistance of large arteries, the hypertensive effect
of ACE DD might be through an increased left
ventricular mass or atherosclerosis of
large arteries. Actually, the maximum odds ratio was observed in the
association with systolic hypertension. We did not examine
whether or not ACE and plasma concentration correlate, and
the difference of SBP in men between DD and II
was only 3.4 mm Hg in the present study (Table 3
).
Other limitations underlie this study. We did not make any adjustments
for medication, dietary factors, habits, and exercise, which seem to
affect blood pressure variance. However, it is also true that these
interventions also produce bias and alter the results. We would rather
conclude that ACE DD is associated with predisposition to
hypertension in men in a general Japanese population.
| Acknowledgments |
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Received June 15, 1999; revision received November 9, 1999; accepted December 2, 1999.
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