Download Genetic Polymorphisms of N-Acetyltransferases 1 and 2 and Gene

Vol. 9, 557–562, June 2000
Cancer Epidemiology, Biomarkers & Prevention
Genetic Polymorphisms of N-Acetyltransferases 1 and 2 and Gene-Gene
Interaction in the Susceptibility to Childhood Acute
Lymphoblastic Leukemia1
Maja Krajinovic, Chantal Richer, Hugues Sinnett,
Damian Labuda, and Daniel Sinnett2
Service d’Hématologie-Oncologie, Centre de Cancérologie Charles-Bruneau,
Centre de Recherche, Hôpital Sainte-Justine (M. K., C. R., H. S., D. L., D. S.),
and Département de Pédiatrie, Université de Montréal, Montreal, Quebec, H3T
1C5 Canada (D. L., D. S.).
Abstract
Acute lymphoblastic leukemia (ALL) is the most common
pediatric cancer. In utero and postnatal exposures to
various carcinogens may play a role in the etiology of this
disease. N-acetyltransferases, encoded by the NAT1 and
NAT2 genes are involved in the biotransformation of
aromatic amines present in tobacco smoke, environment,
and diet. Their rapid and slow acetylation activity alleles
have been shown to modify the risk to a variety of solid
tumors in adults. To investigate the role of NAT1 and
NAT2 variants as risk-modifying factors in
leukemogenesis, we conducted a case-control study on 176
ALL patients and 306 healthy controls of FrenchCanadian origin. Slow NAT2 acetylation genotype was
found to be a significant risk determinant of ALL (odds
ratio, 1.5; 95% confidence interval, 1.0 –2.2) because of
overrepresentation of the alleles NAT2*5C and *7B and
underrepresentation of NAT2*4. Besides a slight increase
in NAT1*4 allele frequency among cases, no independent
association of NAT1 acetylation genotypes and ALL risk
was observed. However, the risk associated with NAT2
slow acetylators was more apparent among homozygous
individuals for NAT1*4 (odds ratio, 1.9; 95% confidence
interval, 1.1–3.4). When NAT2 slow acetylators were
considered together with the other risk-elevating
genotypes, GSTM1 null and CYP1A1*2A, the risk of ALL
increased further, which showed that the combination of
these genotypes is more predictive of risk then either of
them independently. These findings suggest that
leukemogenesis in children is associated with carcinogen
metabolism and consequently related to environmental
exposures.
Received 10/18/99; revised 3/22/00; accepted 3/28/00.
The costs of publication of this article were defrayed in part by the payment of
page charges. This article must therefore be hereby marked advertisement in
accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1
Supported by the Fondation Charles-Bruneau and Power Corporation Inc/
Fondation Hôpital Ste-Justine.
2
To whom requests for reprints should be addressed, at Centre de Cancérologie
Charles-Bruneau, Hôpital Sainte-Justine, 3175 Côte Ste-Catherine, Montréal
(Québec), H3T 1C5, Canada. Phone: (514) 345-4931; Fax: (514) 345-4731;
E-mail: [email protected].
Introduction
ALL3 is the most frequent form of cancer affecting children. As
a sporadic cancer, it can be considered as a complex disease in
which the effect of a series of low penetrance genes, modulated
by external factors, modify the individual’s risk of cancer (1).
Despite many efforts, little is known about leukemogenesis,
particularly with respect to genetic susceptibility and environmental factors (2–5). Individuals having a modified ability to
metabolize carcinogens seem to be at increased risk of cancer
(see review by Perera; Ref. 6). Furthermore, infants and children may be at greater risk than adults from a variety of
environmental toxicants because of differential exposure and/or
physiological immaturity (7–9). Therefore, functional polymorphisms in genes encoding carcinogen-metabolizing enzymes
may have relevance in determining susceptibility to pediatric
cancer. Recently, we showed that the GSTM1 null and
CYP1A1*2A genotypes were both significant predictors of ALL
risk in children (10), which suggests that polymorphisms in
genes that encode carcinogen-metabolizing enzymes may indeed play a role in leukemogenesis.
N-acetyltransferases 1 (NAT1) and 2 (NAT2) are conjugating enzymes involved in the metabolism of aryl- and heterocyclic amines (11, 12). Genetic polymorphisms that have been
described in both NAT1 and NAT2 genes correlate with biochemical phenotypes ranging from slow to fast acetylators
(11–16). Associations have been reported between these DNA
variants and the risk of a number of cancers including head and
neck, lung, breast, laryngeal and bladder cancers (14, 17–21) as
well as colorectal carcinomas (16, 22). Interestingly, both fast
and slow NAT2 acetylators were shown to represent susceptibility factors in different carcinomas (13, 14, 19, 21–25). Such
a dual effect is presumably attributable to differences in biochemical pathways of carcinogen activation in the liver and in
other organs that become eventually affected (14, 21, 22). The
prevalence of acetylator variants varies remarkably among different populations (11, 12). Therefore, special care has to be
taken to avoid interpretation errors attributable to population
heterogeneity. We recently proposed that French-Canadians
who represent a population founded in the 17th century by
immigrants from France (26, 27) constitute an appropriate
genetic model for such genetic epidemiology studies (10).
Here we report a case-control study on the relationship
between DNA variants in NAT1 and NAT2 genes and the
susceptibility to childhood ALL in the French-Canadian population from the Province of Quebec, Canada. We also exam-
3
The abbreviations used are: ALL, acute lymphoblastic leukemia; GSTM1 and
GSTT1, glutathione-S-transferase M1 and T1; CYP1A1, cytochrome P450 1A1;
NAT1 and NAT2, N-acetyltransferases 1 and 2; OR, odds ratio; CI, confidence
interval; WT, wild type.
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Role of NAT1 and NAT2 Polymorphisms in Childhood ALL
Fig. 1. Schematic illustration of NAT1 allelic variants. The WT allele (NAT1*4) and allelic variants tested in this study are shown. The NAT1*3 allele is characterized
by a silent C/A substitution at position 1095. When accompanied by T/A substitution at the position 1088 leading to the shift in a polyadenylation signal, it defines NAT1*10.
In addition to the diagnostic polymorphism at the position 640 (Ser-to-Ala replacement at codon 214), NAT1 *11 allele is also associated with other nucleotide changes
(indicated in italics): C/T at ⫺344, A/T at ⫺40, G/A at 445, G/A at 459, a 9-bp deletion between positions 1065 and 1090, and by C/A substitution at position 1095. A
G-to-A substitution at position 560 (Arg to Glu replacement at codon 187) on the NAT1*10 background defines NAT1*14A allele. A C-to-T substitution at the position
559 (change of Arg-to-stop codon) defines NAT1*15 allele. Numbering of nucleotide positions for NAT1 are as in Deitz et al. (30).
Fig. 2. Schematic illustration of NAT2 allelic variants. The WT allele (NAT2*4) and allelic variants analyzed in this study are shown. The NAT2*12A is characterized
by an A-to-G base substitution at position 803 (Lys-to-Arg substitution at codon 268). The NAT2*5A allele is characterized by a T/C substitution at position 341 (Ile-to-Thr
replacement at codon 114), which is accompanied by silent C-to-T mutation at position 481. The base substitution at the position 803 on the NAT2*5A background defines
the NAT2*5B allele. NAT2*5C differs from NAT2*5B by the absence of a mutation at position 481. The NAT2*6A allele is characterized by a G/A substitution at position
590 (Arg-to-Gln replacement at codon 197). NAT2*7B allele is defined by G-to-A substitution at position 857 causing Gly-to-Glu replacement at codon 286. Numbering
of positions is according to Cascorbi et al. (14).
ined the effect of the combined multilocus genotypes on childhood ALL susceptibility.
Materials and Methods
Subjects. Childhood ALL patients (n ⫽ 176) were diagnosed
in the Division of Hematology-Oncology of Ste-Justine Hospital, Montreal, Canada, between August 1988 and September
1997. They comprised 108 males and 68 females with a median
age of 6.0 years. The distribution of ALL subtypes was as
follows: 142 pre-B and 21 T-cell ALLs and 13 with undetermined lineage. A control group (n ⫽ 306) was randomly
selected from a large institutional DNA bank. All of the participants were of French origin and resided in the Province of
Quebec, Canada. The inclusion criteria for patients and controls
have been described previously (10). The Institutional Review
Board approved the research protocol, and informed consent
was obtained from all of the participating individuals and/or
their parents.
Genotyping. DNA was isolated from buccal epithelial cells,
peripheral blood, or bone marrow in remission as described in
Baccichet et al. (28). All of the selected polymorphisms in
NAT1 (C559T, G560A, T640G, T1088A, and C1095A) and
NAT2 (T341C, C481T, G590A, A803G, and G857A) were
revealed by allele-specific oligonucleotide (ASO) hybridization
assays (29). In some cases the NAT1 and NAT2 genotypes were
confirmed by PCR-RFLP as described in Deitz et al. (30) and
Cascorbi et al. (14), respectively. The alleles defined by these
polymorphisms are given in Fig. 1 and 2.
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Cancer Epidemiology, Biomarkers & Prevention
Table 1
NAT2 allele
Rapid
*4
*12A
None
803
Slow
*5A
*5B
*5C
*6A
*7B
341, 481
341, 481, 803
341, 803
282, 590
282, 857
Total
a
Linkage of mutations (position)
Frequency of NAT2 alleles in ALL patients and controls
ALL patients (n ⫽ 176)
Controls (n ⫽ 291)
ORa
95% CI
P
25.9
0.3
0.6
2.5
0.5–0.9
0.4–15.0
0.01
0.4
2.4
44.2
1.0
24.9
1.2
1.6
0.9
3.1
1.2
2.9
0.7–3.4
0.7–1.2
1.1–8.5
0.9–1.6
1.1–7.4
0.3
0.5
0.02
0.3
0.03
n
%
n
%
65
3
18.5
0.9
151
2
13
148
11
100
12
3.7
42.0
3.1
28.4
3.4
14
257
6
145
7
352
100
582
100
ORs were calculated from the ratio of the number of alleles of interest versus all of the other alleles in ALL patients compared with the ratio in control individuals.
Statistics. The test for case-control differences in the distribution of the genotypes was based on ␹2 statistics. The level of
significance was calculated by Fisher’s exact test. ORs were
used to measure the strength of association between the tested
genotypes and ALL risk. Crude ORs are given with 95% CIs.
Unconditional logistic analysis was used to compute age and
gender as covariables as well as the effect of combined genotypes at risk of ALL susceptibility. All of the statistical tests
were based on two-tailed probability and were performed using
SPSS version 7.5. Linkage disequilibrium between NAT1 and
NAT2 alleles was tested with the software package GenePop
(version 3.1).
Results
The genotypes at 10 polymorphic sites in NAT1 and NAT2
genes (Fig. 1 and 2) were obtained for 176 children with ALL
and 306 healthy controls, both groups consisted of FrenchCanadians residing in the Province of Quebec, Canada. The
selected polymorphisms define the most common allelic variants found in populations of European descent (11, 31). Some
individuals were not successfully genotyped for the whole set
of tested polymorphisms, thus explaining a certain variation in
the total number of samples listed in Tables. In this study, both
pre-B and T-cell ALLs were considered together because no
significant differences were observed in terms of the tested
genotypes (data not shown).
The frequency of NAT2 alleles as well as the distribution
of the genotypes in ALL patients and controls are given in
Tables 1 and 2, respectively. The observed allelic frequencies
were similar to those reported in other populations of European
descent (11, 29). Of note, we did not observe linkage disequilibrium between NAT1 and NAT2 loci as reported elsewhere
(31). The allele frequency distribution among ALL patients
differed from the control group: NAT2*5C and *7B were overrepresented in the patient group, whereas NAT2*4 was underrepresented (Table 1). When genotypes were determined, we
found that those predicting a slow NAT2 acetylator phenotype
(so-called NAT2 slow-acetylation genotype), i.e., two copies of
any “slow” allele (*5A, *5B, *5C, *6A, or *7B), was present in
64.8% of the patients as compared with 54.6% of controls
(Table 2). These results suggest that slow-acetylation activity of
NAT2 is associated with an increased risk of ALL (OR, 1.5;
95%CI, 1.0 –2.2; P, 0.03). At the same time, a significant
decrease in NAT2 rapid-acetylation genotypes (presence of at
least one copy of allele *4 or *12A) among cases pointed to a
protective role of NAT2 activity (OR, 0.7; 95% CI, 0.4 –1.0; P,
Table 2 Distribution of NAT2 genotypes in children with ALL and controls
The distribution of NAT2 genotypes between cases and controls differs significantly, ␹2 ⫽ 31.126; P ⫽ 0.04. Only the genotypes detected in at least one of the
groups are listed. ORs with 95% CIs and corresponding P values are given for
rapid and slow acetylator genotypes (in bold), *4/*4, and *4/*12A individuals
together, *4/*4 homozygous individuals, and NAT2 *4 heterozygous individuals
(in italics).
ALL patients
Controls
n
%
n
%
5
1
2.8
0.6
20
1
Genotype
Rapid acetylationa
*4/*4
*4/*12A
Total
OR (95% CI)
P
6.9
0.3
0.3 (0.1–1.0)
0.03
0.4 (0.2–1.0)
0.06
6
3.4
21
7.2
*4/*5A
*4/*5B
*4/*5C
*4/*6A
*4/*7B
*5B/12A
*6A/12A
2
28
0
21
3
1
1
1.1
15.9
0.0
12.0
1.7
0.6
0.6
3
75
2
30
0
1
0
1.0
25.8
0.7
10.3
0.0
0.3
0.0
Total
56
31.8
111
38.2
0.7 (0.5–1.1)
0.09
Sum of rapid
62
35.2
132
45.4
0.7 (0.4–1.0)
0.03
Slow acetylationb
*5A/*5B
*5A/*5C
*5A/*6A
*5B/*5B
*5B/*5C
*5B/*6A
*5B/*7B
*5C/*6A
*6A/*6A
*6A/*7B
7
1
3
29
9
38
7
1
17
2
4.0
0.6
1.7
16.5
5.1
21.6
4.0
0.6
9.7
1.1
7
1
3
51
3
64
5
0
23
2
2.4
0.3
1.0
17.5
1.0
22.0
1.7
0.0
7.9
0.7
1.5 (1.0–2.2)
0.03
Sum of slow
Total
114
64.8
159
54.6
176
100.0
291
100.0
a
Rapid acetylation genotype corresponds to the presence of at least one copy of
NAT2*4 or NAT2*12A.
b
Slow acetylation genotype corresponds to the presence of two alleles with slow
acetylation capacity.
0.03; Table 2), particularly in individuals homozygous for the
NAT2*4 allele (Table 2). Multivariate analysis that included
age and gender as covariables did not change the interpretation
of these results.
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Role of NAT1 and NAT2 Polymorphisms in Childhood ALL
Table 3
NAT1 allele
Linkage of mutationsa
(position)
*4
*3
*10
*11
*14A
*15
None
1095
1088, 1095
640, 1095
560, 1088, 1095
559
Total
Frequency of NAT1 alleles in childhood ALL patients and controls
ALL patients (n ⫽ 155)
Controls (n ⫽ 306)
n
%
n
%
244
3
51
6
5
0
78.7
1.0
16.8
1.9
1.6
0.0
447
16
122
20
5
2
73.0
2.6
19.9
3.3
0.8
0.3
310
100
612
ORb (95% CI)
P
1.4 (1.0–1.9)
0.4 (0.1–1.3)
0.8 (0.6–1.1)
0.6 (0.2–1.5)
2.0 (0.6–6.9)
0.4 (0.02–8.2)
0.06
0.1
0.2
0.3
0.3
0.6
100
a
Only the polymorphisms analyzed in this study are given. For instance, despite the presence of other polymorphisms associated with allele *11 (see Fig. 1), the nucleotide
substitution at position 640 was considered a diagnostic change for NAT1 *11.
b
ORs were calculated from the ratio of the number of alleles of interest versus all other alleles in ALL patients compared with the ratio in control individuals.
Table 4
Distribution of NAT1 genotypes in children with ALL and controls
ALL patients
Genotype
n
%
n
%
99
63.9
172
56.2
*4/*3
*4/*11
*4/*14A
1
4
3
0.6
2.6
1.9
12
14
4
3.9
4.6
1.3
Sum of */*4a
7
5.1
30
9.8
*3/*3
*3/*11
*11/*11
0
1
0
0.0
0.6
0.0
1
0
1
0.3
0.0
0.3
108
69.7
204
66.7
5
1
38
1
2
0
3.2
0.6
24.5
0.6
1.3
0.0
20
2
73
4
1
2
6.5
0.7
23.9
1.3
0.3
0.7
47
30.3
102
33.3
155
100.0
306
100.0
*4/*4a
Sum of non-*10b
*10/*10
*10/*3
*10/*4
*10/*11
*10/*14A
*10/*15
Sum of -*10b
Total
Table 5
Controls
OR (95% CI)
P
1.4 (0.9–2.1)
0.1
Association between NAT1 and NAT2 genotypes and childhood ALL
NAT1a
NAT2b
Cases
(n ⫽ 154)
Controls
(n ⫽ 266)
non-*4/*4
non-*4/*4
*4/*4
*4/*4
Rapid
Slow
Rapid
Slow
25
31
31
67
64
57
56
89
OR (95% CI)
P
1.0
1.9 (1.1–3.4)
0.03
a
1.0 (0.4–2.5)
1.0
1.1 (0.8–1.7)
0.5
0.9 (0.6–1.3)
0.5
a
The NAT1*4 was the only NAT1 allele with increased frequency in cases versus
controls; therefore, OR was estimated for homozygous and heterozygous (*/*4)
NAT1*4 individuals.
b
Because the presence of at least one copy of the NAT1*10 allele is presumably
associated with elevated acetylation capacity (16), individuals were stratified
according to the presence or absence of the allele *10.
The NAT1 genotyping data for the patient and the control
group are reported in Tables 3 and 4. A modest increase of
NAT1*4 allele is observed among ALL patients (OR, 1.4; 95%
CI, 1.0 –1.9; P, 0.06) compared with the controls (Table 3),
which could explain a higher, although not significant, prevalence (OR, 1.4; 95% CI, 0.9 –2.1; P, 0.1) of patients homozygous for this allele (Table 4). The patients and controls were
also arbitrarily grouped based on the presence or absence of the
putative rapid allele *10 (16). The frequency of NAT1*10
carriers and noncarriers did not differ between cases and controls (Table 4), which suggests that the NAT1 acetylation genotype is not independently related to overall risk of childhood
ALL. Involvement of NAT1 and NAT2 enzymes in similar
metabolic pathways prompted us to examine the effect of the
combined genotypes for these loci (Table 5). An increase in the
risk of ALL (OR, 1.9; 95%CI, 1.1–3.4; P, 0.03) for individuals
with NAT2 slow acetylators that are homozygous for the
NAT1*4 allele compared with the risk for individuals without
these genotypes was observed.
*4/*4, homozygous individuals for NAT1*4 allele; non-*4/*4, nonhomozygous
individuals for NAT1*4.
b
Rapid, rapid acetylation genotype; Slow, slow acetylation genotype.
From a previous study of the same case-control group, we
reported that children carrying the GSTM1 null genotype or at
least one CYP1A1*2A allele had an increased risk of ALL (10).
Here, we investigated whether this risk was increased further by
additionally considering NAT2 genotypes. The reference group
(OR, 1.0) was defined as children having the following “lowrisk” genotypes: NAT2 rapid acetylation, presence of GSTM1,
and absence of CYP1A1*2A allele. The estimated risk of ALL
for all of the combinations of genotypes at risk is given in Table
6. The presence of only one risk-elevating genotype did not
influence the risk. However, the overall risk of ALL increased
with the number of risk-increasing genotypes (P for trend,
0.0001), with ORs of 2.7 (95%CI, 1.4 – 4.9; P, 0.002) and 3.1
(95%CI, 1.1– 8.4; P, 0.03) for two and three genotypes, respectively (Table 6).
Discussion
ALL in children offers a unique opportunity to examine the
effect of carcinogen-metabolism genes in the risk of pediatric
cancers (10). The young ages of patients and, thus, a short
latency period between the appearance of the initiating mutation and the detection of tumor cells should facilitate the identification of risk factors, as compared with adult cancer patients
in whom many factors come into play because of long latency
periods. Here, we determined the frequencies of NAT1 and
NAT2 allelic variants in French-Canadians from Quebec, Canada. This population was founded by a few thousand immigrants from France in the 17th century (26, 27). After the
British conquest in the middle of 18th century, the flow of
French immigrants practically ceased. However, because of a
large demographic growth, this population grew naturally and
expanded to about 10 million in Quebec and elsewhere in North
America. Despite the founder effect (26), the overall frequencies of the genotypes tested in controls agree with those reported for other populations of European descent (11–14, 16,
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Cancer Epidemiology, Biomarkers & Prevention
Table 6
Association between NAT2, GSTM1, and CYP1A1 genotypes and childhood ALL
GSTM1
CYP1A1*2Aa
NAT2b
Cases (n ⫽ 174)
Controls (n ⫽ 285)
OR (95% CI)
No genotypes at risk
Present
⫺/⫺
Rapid
19
53
1.0 (referent)
One genotype at risk
Null
Present
Present
⫺/⫺
⫺/⫺
⫹/⫹; ⫺/⫹
Rapid
Slow
Rapid
29
33
2
60
69
9
1.3 (0.7–2.7)
1.3 (0.7–2.6)
0.6 (0.1–3.1)
0.5
0.5
0.7
64
138
1.3 (0.7–2.4)
0.5
60
9
11
69
10
5
2.4 (1.3–4.5)
2.5 (0.9–7.1)
6.1 (1.9–20.1)
0.006
0.1
0.003
80
84
2.7 (1.4–4.9)
0.002
11
10
3.1 (1.1–8.4)
0.03
Total
Two genotypes at risk
Null
Present
Null
⫺/⫺
⫹/⫹; ⫺/⫹
⫹/⫹; ⫺/⫹
Slow
Slow
Rapid
Total
Three genotypes at risk
Null
⫹/⫹; ⫺/⫹
Slow
P
⫺/⫺, absence of alleles; ⫹/⫹; ⫺/⫹, presence of at least one allele.
b
Rapid, rapid acetylation genotype; Slow, slow acetylation genotype (see in Table 2).
a
29, 32), which suggests that the implications of our results
could be extended to these groups as well.
We found that children carrying NAT2 slow-acetylation
genotypes were at increased risk of developing ALL (OR, 1.5;
95% CI, 1.0 –2.2), mainly because of the overrepresentation of
alleles NAT2*5C and *7B. We observed a lower prevalence of
the NAT2*4 allele in the patients’ group, which may suggest a
protective role for this allele. The effect was more obvious in
homozygous individuals as it was also reported by others (14).
To our knowledge, this is the first study documenting an association between NAT2 variants and the risk of hematological
malignancies, particularly in children. However, these data are
in agreement with the studies of solid neoplasias in adults that
report that NAT2 slow-acetylator individuals are at greater risk
of head and neck, breast, and laryngeal cancers (17–19) as well
as bladder cancer (20, 21). When NAT1*10 was considered
alone or combined with NAT2 slow-acetylation genotype, our
data provided no evidence of involvement of this allele in ALL
susceptibility. In other studies, NAT1*10 has been associated
with an increase of N-acetyltransferase activity (16), higher
levels of DNA adducts (33), and an elevated risk of colon,
bladder, or breast carcinomas (16, 23, 32). The risk of cancer
was accentuated when NAT1*10 genotypes were combined
with NAT2 at-risk genotypes (16, 32). However, in light of
conflicting data in the literature, the role of NAT1*10 in tumorigenesis still remains unclear (34 –36). On the other hand, we
noted a slight increase in the frequency of NAT1*4 among
cases, which, when combined with NAT2 slow-acetylator genotypes, further increases the risk of ALL (OR, 1.9; 95% CI,
1.1–3.4). Taken together, the results for NAT1 should be interpreted with caution because the functional significance of NAT1
variants remains to be clarified.
It is difficult to predict how the genotypes at risk will
modify the infant’s (or fetus’) response to different exposures.
Epidemiological studies have led to the suggestion that in utero
and postnatal exposures to various biological, physical and
chemical factors may be important determinants of childhood
ALL (7, 37, 38). Children may be at greater risk than adults
from toxic substances because of differential exposure or physiological immaturity (7, 9, 19). We have recently shown that the
risk of ALL among children carrying certain CYP1A1 variants
was modified by maternal exposure to pesticides during the
pregnancy (39). Both NAT1 and NAT2 enzyme activities are
detectable in human placentas (40, 41), although it seems that
placental N-acetylation activity is predominantly attributable to
NAT1 (11, 40 – 42). Thus, it is possible that genetically deter-
mined variability in N-acetylation of aromatic amines present in
different environmental and occupational pollutants like dyes,
tobacco smoke, antioxidants, medications, or pesticides may
confer cancer susceptibility on children (13, 14, 19, 21–25).
Predominance of the competing N-oxidation in subjects with
NAT2 slow acetylation would lead to the formation of aryl
hydroxylamines. Because NAT1 is widely expressed in different tissue (11, 43), it can act locally, performing O-acetylation
of hydroxilated arylamines, which will result in the formation
of arylnitrenium ions and DNA adducts (44).
Recently, we reported that the GSTM1 null genotype and
the presence of at least one CYP1A1*2A allele were significant
predictors of ALL risk (10). When these two genotypes were
combined with genotypes predicting NAT2 slow acetylators,
we found that the presence of only one risk-elevating genotype
had little effect on OR estimates. However, the combination of
risk-elevating genotypes seemed to confer an increased risk of
ALL among the carriers compared with those with the more
beneficial genotypes (OR, 2.7; 95% CI, 1.4 – 4.9; and OR, 3.1,
95% CI, 1.1– 8.4, respectively). These results are similar to
those obtained in nonhematological malignancies for the combined effect of NAT2 and GSTM1 (19, 25, 45). However, the
basis of synergy between CYP1A1 and NAT2 is less obvious
because they are involved in different metabolic pathways. This
effect could be mediated through CYP1A2 that is involved in
the first step of the activation of the aromatic amines (13). It has
been recently shown that CYP1A2 activity was higher in individuals with GSTM1 null genotype or heterozygous for
CYP1A1 variants compared with individuals with GSTM1 or no
CYP1A1 polymorphisms (46). Consequently, slow acetylators
may not be able to compete with high activity of CYP1A2 for
aromatic amines.
In this study, the simultaneous analysis of several loci
suggests that the combination of risk-elevating genotypes is
more predictive of ALL risk than when they are taken independently. In other words, the etiology of childhood ALL
cannot be explained by allelic variability at a single locus
probably, because of the complexity of xenobiotics metabolism
and the diversity of chemicals to which individuals are exposed.
Acknowledgments
We thank all of the patients and control subjects who participated in this study as
well as the physicians and the clinical staff for their collaboration and Ulrike
Brockstedt for critical reading of the manuscript. D. S. is a scholar of the Fonds
de la Recherche en Santé du Québec.
Downloaded from cebp.aacrjournals.org on August 3, 2017. © 2000 American Association for Cancer Research.
561
562
Role of NAT1 and NAT2 Polymorphisms in Childhood ALL
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Genetic Polymorphisms of N-Acetyltransferases 1 and 2 and
Gene-Gene Interaction in the Susceptibility to Childhood
Acute Lymphoblastic Leukemia
Maja Krajinovic, Chantal Richer, Hugues Sinnett, et al.
Cancer Epidemiol Biomarkers Prev 2000;9:557-562.
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