MTHFR polymorphisms, dietary folate intake and breast cancer risk in Chinese women.
ABSTRACT To evaluate the relationship between dietary folate intake and genetic polymorphisms of 5,10-methylenetetrahydrofolate reductase (MTHFR) with reference to breast cancer risk, we conducted a case-control study with 669 cases and 682 population-based controls in the Jiangsu Province of China. MTHFR C677T and A1298C genotypes were identified using PCR-RFLP (restrictrion fragment length polymorphism) methods. Dietary folate intake was assessed using an 83-item food frequency questionnaire. Odds ratios (ORs) were estimated with an unconditional logistic model. The frequencies of MTHFR C677T C/C, C/T and T/T genotypes were 32.37, 48.88 and 18.75% in cases and 37.66, 48.24 and 14.10% in controls, respectively. The difference in distribution was significant (chi(2)=6.616, P=0.037), the T/T genotype being associated with an elevated OR (adjusted for age, menopausal status, body mass index (BMI), income, work intensity and status of smoking and drinking) for breast cancer (1.62, 95% confidence interval (95% CI): 1.14-2.30). The frequencies of MTHFR A1298C A/A, A/C and C/C were 71.47, 27.08 and 1.44% in cases and 68.11, 30.13 and 1.76% in controls, respectively, with no significant differences being found (chi(2)=1.716, P=0.424). A significant inverse relationship was observed between folate intake and breast cancer risk. Compared with the lowest tertile of folate intake, the adjusted OR for breast cancer in the top tertile was 0.70 (95% CI: 0.53-0.92). However, no significant interaction was observed between folate intake and the MTHFR C677T polymorphism. Among individuals with the MTHFR A1298C A/A genotype, adjusted ORs for breast cancer were 0.89 (0.62-1.27) and 1.69 (1.20-2.36) for the second to the third tertile of folate intake compared with the highest folate intake group (tread test, P=0.0008). The findings of this study suggest that MTHFR genetic polymorphisms and dietary intake of folate may modify susceptibility to breast cancer.
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ABSTRACT: Folate plays a pivotal role in DNA synthesis, repair, methylation and homocysteine (Hcy) metabolism. Therefore, alterations in the folate-mediated one-carbon metabolism may lead to abnormal methylation proliferation, increases of tumor/neoplasia and vein thrombosis/cardiovascular risk. The serine hydroxymethyhransferase (SHMT), methionine synthase (MS), methionine synthase reductase (MTRR) and cystathionine beta synthase (CBS) regulate key reactions in the folate and Hcy metabolism. Therefore, we investigated whether the genetic variants of the SHMT, MS, MTRR and CBS gene can affect plasma Hcy levels and are associated with breast cancer risk. Genotyping was performed by PCR-RFLP method. Plasma Hcy levels were measured by the fluorescence polarization immunoassay on samples of 96 cases and 85 controls. (a) The SHMT 1420 T, MS 2756G, MTRR 66G allele frequency distribution showed significant difference between case and controls (p < 0.01 ~ 0.05). (b) The concentration of plasma Hcy levels of SHMT 1420TT was significantly lower than that of the wild type, while the plasma Hcy levels of MS 2756GG, CBS 699TT/1080TT significantly higher than that of the wild type both in case and controls. The plasma Hcy levels of MTRR 66GG was significantly higher than that of wild type in cases. The plasma Hcy levels of the same genotype in cases were significantly higher than those of controls except SHMT 1420CC, MS 2756AA, MTRR 66GG; (c) Multivariate Logistic regression analysis showed that SHMT C1420T (OR = 0.527, 95% CI = 0.55 ~ 1.24), MS A2756G (OR = 2.32, 95% CI = 0.29 ~ 0.82), MTRR A66G (OR = 1.84, 95% CI = 0.25 ~ 1.66) polymorphism is significantly associated with breast cancer risk. And elevated plasma Hcy levels were significantly linked to increased risk of breast cancer (adjusted OR = 4.45, 95% CI = 1.89-6.24 for the highest tertile as compared with the lowest tertile). The current study results seem to suggest a possibility that SHMT C1420T mutation may be negatively correlated with breast cancer susceptibility; while MS A2756G and MTRR A66G mutation may be positively associated with breast cancer risk. SHMT C1420T, MS A2756G, MTRR A66G, CBS C1080T, CBS C699T locus mutation may be factors affecting plasma levels of Hcy. The plasma Hcy levels could be metabolic risk factor for breast cancer risk to a certain extent.Hereditary Cancer in Clinical Practice 01/2014; 12(1):2. · 1.71 Impact Factor
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ABSTRACT: Background:Many epidemiological studies have investigated the association between folate intake, circulating folate level and risk of breast cancer; however, the findings were inconsistent between the studies.Methods:We searched the PubMed and MEDLINE databases updated to January, 2014 and performed the systematic review and meta-analysis of the published epidemiological studies to assess the associations between folate intake level, circulating folate level and the overall risk of breast cancer.Results:In all, 16 eligible prospective studies with a total of 744 068 participants and 26 205 breast cancer patients and 26 case-control studies with a total of 16 826 cases and 21 820 controls that have evaluated the association between folate intake and breast cancer risk were identified. Pooled analysis of the prospective studies and case-control studies suggested a potential nonlinearity relationship for dietary folate intake and breast cancer risk. Prospective studies indicated a U-shaped relationship for the dietary folate intake and breast cancer risk. Women with daily dietary folate intake between 153 and 400 μg showed a significant reduced breast cancer risk compared with those <153 μg, but not for those >400 μg. The case-control studies also suggested a significantly negative correlation between the dietary folate intake level and the breast cancer risk. Increased dietary folate intake reduced breast cancer risk for women with higher alcohol intake level, but not for those with lower alcohol intake. No significant association between circulating folate level and breast cancer risk was found when the results of 8 identified studies with 5924 participants were pooled.Conclusions:Our studies suggested that folate may have preventive effects against breast cancer risk, especially for those with higher alcohol consumption level; however, the dose and timing are critical and more studies are warranted to further elucidate the questions.British Journal of Cancer advance online publication, 25 March 2014; doi:10.1038/bjc.2014.155 www.bjcancer.com.British Journal of Cancer 03/2014; · 5.08 Impact Factor
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ABSTRACT: There is conflicting epidemiological evidence on the role of folate and breast cancer risk. We conducted a systematic review and quantitative meta-analysis of folate intake and folate blood levels and the risk of breast cancer. Four electronic databases (Medline, PubMed, Embase, and Current Contents Connect) were searched to April 11, 2014, with no language restrictions for observational studies that measured folate intake or blood levels and the risk of breast cancer. The meta-analysis of dietary folate intake comprising 36 studies with 34,602 cases, and a total sample size of 608,265 showed a decreased risk of breast cancer, with an odds ratio (OR) of 0.84 [95 % confidence interval (CI) 0.77-0.91]. When stratified by menopausal status and by study design, none of the meta-analyses of prospective studies showed any statistically significant decrease in the risk of breast cancer. The meta-analysis of total folate showed no statistically significant association with breast cancer OR of 0.98 (95 % CI 0.91-1.07). There was no significant association between either dietary or total folate intake and breast cancer when stratified by hormonal receptor status. The meta-analysis of blood folate levels found no significant association with the risk of breast cancer, with an OR of 0.86 (95 % CI 0.60-1.25). Breast cancer does not appear to be associated with folate intake, and this did not vary by menopausal status or hormonal receptor status. Folate blood levels also do not appear to be associated with breast cancer risk.Breast Cancer Research and Treatment 04/2014; · 4.47 Impact Factor
MTHFR polymorphisms, dietary folate intake and
breast cancer risk in Chinese women
Chang-Ming Gao1, Jin-Hai Tang1, Hai-Xia Cao1, Jian-Hua Ding1, Jian-Zhong Wu1, Jie Wang1, Yan-Ting Liu1,
Su-Ping Li1, Ping Su1, Keitaro Matsuo2, Toshiro Takezaki3and Kazuo Tajima2
To evaluate the relationship between dietary folate intake and genetic polymorphisms of 5,10-methylenetetrahydrofolate
reductase (MTHFR) with reference to breast cancer risk, we conducted a case–control study with 669 cases and 682
population-based controls in the Jiangsu Province of China. MTHFR C677T and A1298C genotypes were identified using
PCR–RFLP (restrictrion fragment length polymorphism) methods. Dietary folate intake was assessed using an 83-item food
frequency questionnaire. Odds ratios (ORs) were estimated with an unconditional logistic model. The frequencies of MTHFR
C677T C/C, C/T and T/T genotypes were 32.37, 48.88 and 18.75% in cases and 37.66, 48.24 and 14.10% in controls,
respectively. The difference in distribution was significant (v2¼6.616, P¼0.037), the T/T genotype being associated with an
elevated OR (adjusted for age, menopausal status, body mass index (BMI), income, work intensity and status of smoking and
drinking) for breast cancer (1.62, 95% confidence interval (95% CI): 1.14–2.30). The frequencies of MTHFR A1298C A/A,
A/C and C/C were 71.47, 27.08 and 1.44% in cases and 68.11, 30.13 and 1.76% in controls, respectively, with no significant
differences being found (v2¼1.716, P¼0.424). A significant inverse relationship was observed between folate intake and
breast cancer risk. Compared with the lowest tertile of folate intake, the adjusted OR for breast cancer in the top tertile was
0.70 (95% CI: 0.53–0.92). However, no significant interaction was observed between folate intake and the MTHFR C677T
polymorphism. Among individuals with the MTHFR A1298C A/A genotype, adjusted ORs for breast cancer were 0.89
(0.62–1.27) and 1.69 (1.20–2.36) for the second to the third tertile of folate intake compared with the highest folate intake
group (tread test, P¼0.0008). The findings of this study suggest that MTHFR genetic polymorphisms and dietary intake of folate
may modify susceptibility to breast cancer.
Journal of Human Genetics (2009) 54, 414–418; doi:10.1038/jhg.2009.57; published online 26 June 2009
Keywords: breast cancer; folate; genetic polymorphisms; methylenetetrahydrofolate reductase; susceptibility
Folate has an important role in DNA methylation, synthesis and
repair, and there is epidemiological evidence indicating that low intake
may increase the risk for neoplasia, including breast cancer.1,2The
mechanisms linking folate deficiency to cancer development could
include uracil misincorporation, increased DNA strand breaks,
aberrations in DNA methylation and disruption of DNA repair.3,4
The 5,10-methylenetetrahydrofolate reductase (MTHFR) is a key
enzyme in folate metabolism, irreversibly catalyzing the 5,10-methy-
lenetetrahydrofolate reaction to 5-methyltetrahydrofolate, the primary
circulatory form of folate and a carbon donor for remethylation of
homocysteine to methionine. The latter is the precursor for the
universal methyl donor, S-adenosylmethionine. Folate that is not
converted through this pathway enters another pathway that leads
to purine and thymidylate synthesis. Two polymorphisms in the
MTHFR gene that affect the efficiency of folate metabolism have
been described (MTHFR 677 C4T transition in exon 4 and MTHFR
1298 A4C transversion in exon 7).5The MTHFR 677 TT genotype
results in 30% enzyme activity in vitro compared with the CC wild-
type,6whereas the MTHFR 1298 CC genotype has been found to have
60% of the AAwild-type enzyme activity in vitro.7,8These low-activity
genotypes seem to be associated with reduced risk for a variety of
cancers, such as acute lymphocytic leukemia, lung, gastric and color-
ectal cancers.9,10A number of studies have evaluated the association
between the MTHFR genotype and breast cancer, but the results have
Our previous studies16–20have shown relationships between genetic
polymorphisms of MTHFR and susceptibility to stomach, esophageal
and colorectal cancers. To evaluate the relationship between dietary
folate intake and genetic polymorphisms of MTHFR with reference to
breast cancer risk, we conducted this case–control study in Jiangsu
Received 19 January 2009; revised 1 May 2009; accepted 25 May 2009; published online 26 June 2009
1Division of Epidemiology, Jiangsu Province Institute of Cancer Research, Nanjing, China;2Division of Epidemiology and Prevention, Aichi Cancer Center Research Institute,
Nagoya, Japan and3Department of International Island and Community Medicine, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka,
Correspondence: Dr C-M Gao, Division of Epidemiology, Jiangsu Provincial Institute of Cancer Research, 42 Baiziting, Nanjing 210009, China.
Journal of Human Genetics (2009) 54, 414–418
& 2009 The Japan Society of Human Genetics All rights reserved 1434-5161/09 $32.00
MATERIALS AND METHODS
We recruited breast cancer cases using data of the Cancer Registries in Taixing,
Wuxi, Jintan and Huian cities of the Jiangsu Province of China, and also
recruited cases who visited the Jiangsu Province Cancer Hospital from these
cities from June 2004 to December 2007. All cases were histopathologically
diagnosed as having a primary breast cancer. Physicians at the hospital asked
eligible cases to participate in our study, and doctors or nurses interviewed the
participants and collected blood samples from a peripheral vein after obtaining
informed consent. Population-based controls were selected from healthy
residents in 11 villages or towns of Taixing, Wuxi, Jintan and Huian cities.
Doctors of the public health centers randomly selected one or two controls for
each case, after matching for ethnicity and age within 2 years using the records
of residents at the local governmental office, and then asked eligible residents
for their participation. Interviews were conducted and blood samples were
collected as for the cancercases. A total of 669 cases and 682 controls completed
the interview, and of these 624 and 624, respectively, donated blood. A few
patients and residents refused, but the rates for blood sampling were 93.3% for
cases and 91.5% for controls. The ethics committee of the Jiangsu Province
Institute of Cancer Research approved this study.
Data and biological sample collection
All participants completed an in-person interview that used a structured
questionnaire. Dietary intakes were assessed using an 83-item food frequency
questionnaire, capturing 90% of food intake and covering nutrients constitut-
ing up to 90% of the nutrient intake in urban and rural areas of the Jiangsu
province.21Each participant was asked about the frequency of a specific food
that was eaten, followed by a question on the amount typically consumed.
Dietary intakes of folate were calculated according to the consumption of
foods, with Standard Food Composition Tables for China.22
DNA extraction and genotyping
Whole blood was collected into EDTA (ethylenediaminetetraacetic acid)-coated
tubes and centrifuged for 15min, and the buffy coat layer was isolated.
Genomic DNAwas extracted from 200ml of buffy coat using a Qiagen QIAamp
DNA Blood Mini Kit (Qiagen, Valencia, CA, USA). MTHFR C677T and
A1298C mutations were detected after PCR amplification with corresponding
primers as detailed in our previous studies.17–20The restriction enzyme Hinf
was used to distinguish the 677 (C-T) polymorphism. The primers for PCR
GGTG-AGAGTG-3¢. The PCR product was subjected to Hinf I restriction
enzyme digestion, and samples were then analyzed by electrophoresis in 3%
agarose gels stained with ethidium bromide. There were three genotypes of
MTHFR C677T, namely C/C (198bp), C/T (198/175bp) and T/T (175bp). The
restriction enzyme Mboa was used to distinguish the 1298 (A-C) polymorph-
ism. The primers for PCR were 5¢-CTTTGGGGAGCTGAAGGACTACTAC-3¢
and 5¢-CACTTTGTGACCATTCCGGTTTG-3¢. The PCR product was subjected
to Mboa restriction enzyme digestion, and the samples were then analyzed by
electrophoresis in 4% agarose gels stained with ethidium bromide. There were
three genotypes of MTHFR A1298C, namely A/A (56bp), A/C (56/84bp) and
Odds ratios (ORs) were used to measure the association of breast cancer risk
with the MTHFR genotype and intakes of folate. Unconditional logistic
regressions from the statistical package SAS were used to obtain maximum
likelihood estimates of the ORs and their 95% confidence intervals,15after
adjusting for age, BMI, menopausal status, work intensity and status of
smoking and drinking. Age and BMI were included as continuous variables
throughout the study. Tertile distributions of dietary intake of folate among
controls were used to categorize the variables. The probability of the Hardy–
Weinberg equilibrium was assessed by w2-test.
The baseline characteristics of cases and controls are summarized in
Table 1. There were no significant differences between cases and
controls in terms of age, BMI and menopausal status. However,
significant differences were found for income per month, work
intensity, smoking status and alcohol drinking status. Cases also had
a lower intake of folate than controls.
Data for associations between MTHFR genotypes, folate intake and
breast cancer risk are presented in Table 2. The frequencies of MTHFR
C677T C/C, C/T and T/T genotypes were 32.37, 48.88 and 18.75% in
cases and 37.66, 48.24 and 14.10% in controls, respectively, the
difference in distribution being significantly different (w2¼6.616,
P¼0.037). The T/T genotype was associated with an elevated OR
(adjusted for age, menopausal status, BMI, income, work intensity
and status of smoking and drinking) for breast cancer (1.62, 95% CI:
1.14–2.30). The frequencies of MTHFR A1298C A/A, A/C and C/C
Table 1 Comparison of cases and controls by selected descriptive
Heavy physical force work
Light and heavy
physical force work
Light physical force work
Alcohol drinking status
Intake of folate (mg/day)263.00±137.38 285.12±149.610.0047
Abbreviation: BMI, body mass index.
MTHFR polymorphisms, folate and breast cancer
C-M Gao et al
Journal of Human Genetics
were 71.47, 27.08 and 1.44% in cases and 68.11, 30.13 and 1.76% in
controls, respectively, with no significant differences being found
(w2¼1.716, P¼0.424). Among the controls, the distributions of
MTHFR genotypes did not differ from the predicted distribution
under the Hardy–Weinberg equilibrium (P40.05, w2¼0.287 for the
C677T polymorphism and w2¼3.638 for the A1298C polymorphism).
A significant inverse relationship was observed between folate intake
and breast cancer risk. Compared with the lowest tertile of folate
intake, the adjusted OR for breast cancer in the top tertile was 0.70
(95% CI: 0.53–0.92).
Results of associated effect on breast cancer risk between
MTHFR677 and 1298 genotypes are described in Table 3. When
MTHFR677 C/C with 1298 A/A genotypes were considered as the
reference group, MTHFR677 C/C with 1298 C/C genotypes showed
the lowest adjusted OR (0.61; 95% CI: 0.14–2.63). On the other hand,
MTHFR677 T/Twith 1298 A/C genotypes showed the highest adjusted
OR (1.97; 95% CI: 0.86–4.50), but these ORs were not statistically
The data were further analyzed to examine the combined effects of
MTHFR677 and 1298 genotypes and folate intake on risk for breast
cancer (Table 4). Among 677 C/C, C/Tand 1298 A/Agenotypes, the ORs
were increased along with a decrease in folate intake, the trend being
statistically significant for 677 C/T (P¼0.0062) and 1298 A/A genotypes
(P¼0.0008). Compared with the group having the 677 C/C genotype
and high folate intake, the 677 T/T genotype and high or low folate
intake groups all had elevated ORs for breast cancer. The 677
T/T genotype with high folate intake had the highest OR (2.41, 95%
CI: 1.22–4.74) for breast cancer. Among individuals with 1298 A/A and
677 C/T genotypes, ORs for breast cancer were increased along with a
decrease in folate intake, the adjusted ORs for breast cancer being 0.97
(0.53–1.77), 1.06 (0.57–1.97) and 2.19 (1.25–3.83) for the highest to the
third tertile of folate intake, respectively (trend test, P¼0.0005).
In this study of associations of two common polymorphisms in
MTHFR (C677Tand A1298C), a gene that has a central role in folate
metabolism, we found the MTHFR 677 TT genotype to significantly
increase the risk of breast cancer, whereas dietary intake of folate
showed an inverse association with the risk of breast cancer. We also
found that lower folate intake was particularly linked to increased risk
of breast cancer among individuals with MTHFR 1298A/A and
677C/C or 677C/T genotype.
Previous studies have generated inconsistent findings on the
MTHFR polymorphism and folate intake associations with breast
cancer risk. MTHFR 677TT and 1298CC genotypes cause decreased
enzyme activity,6–8and some studies have indicated that the MTHFR
677TT genotype confers greater risk of breast cancer, especially in
women in the premenopausal stage.13,14,23–27Many meta-analysis
studies have also supported this conclusion.11,15On the other hand,
no association between MTHFR genotypes and the risk of breast
cancer was noted in other studies28–32and two meta-analyses.12,33The
reasons for these inconsistent results are not clear, but clearly variation
with ethnicity and environment could contribute to differences in
influence on the development of breast cancer.
It has been shown consistently that the pathophysiological
consequences of MTHFR genetic variants, especially the C677T
polymorphism, are significantly affected by demographic and envir-
onmental factors, such as folate status, age, smoking and alcohol
intake, all parameters that may additionally alter the fine equilibrium
of one carbon metabolism.10,34In particular, the phenotypic effects
of C677T and A1298C polymorphisms are affected by the folate
status.3,6,35It has been suggested that the stability of the polymorphic
enzyme is significantly modified by folate levels. Under conditions of
high intracellular folate, the folate molecule may be able to hold the
variant MTHFR protein in the appropriate and fully functional three-
dimensional form, thus stabilizing the thermolabile structure and
counteracting reduction in enzyme activity.35
Folate is an essential nutrient that supports nucleotide synthesis and
biological methylation reactions. A number of epidemiological studies
have suggested an inverse association between dietary intake and
blood levels of folate and breast cancer risk.34,36,37Several previous
studies have also indicated a gene–nutrient interaction between the
MTHFR C677T polymorphism and dietary folate intake in breast
carcinogenesis, in which the 677TT genotype was associated with an
elevated risk when dietary folate intake was low;14,24,38however, a
meta-analysis12concluded that there was no evidence of an interaction
between folate intake and the MTHFR genotype on breast cancer risk.
Table 2 Adjusted odds ratios (ORs) and 95% confidence intervals
(CIs) for breast cancer with respect to MTHFR polymorphisms and
dietary folate intake
Cases (%) Controls (%)ORa(CI)ORb(CI)
Folate intake (mg/day)
0.71 (0.55–0.92) 0.70 (0.53–0.91)
190 (28.40)227 (33.28) 0.69 (0.53–0.90) 0.70 (0.53–0.92)
Abbreviations: BMI, body mass index; MTHFR, 5,10-methylenetetrahydrofolate reductase.
aORs were adjusted for age and menopausal status.
bORs were adjusted for age, BMI, income, menopausal status, work intensity and status of
smoking and drinking.
Table 3 Interaction between MTHFR C677T and A1298C genotypes
and the odds ratios (ORs) for breast cancer
C677T A1298C Cases (n) Controls (n)ORa(95% CI) ORb(95% CI)
0.77 (0.51–1.15) 0.82 (0.54–1.24)
0.53 (0.12–2.24) 0.61 (0.14–2.63)
1.08 (0.80–1.47) 1.12 (0.82–1.53)
1.04 (0.41–1.53) 1.13 (0.76–1.68)
1.59 (0.46–5.46) 1.50 (0.41–5.50)
1.38 (0.94–2.03) 1.41 (0.95–2.09)
1.90 (0.85–4.26) 1.97 (0.86–4.50)
Abbreviations: BMI, body mass index; CI, confidence interval; MTHFR, 5,10-methyl-
aORs were adjusted by age and menopausal status.
bORs were adjusted by age, BMI, income, menopausal status, work intensity and status of
smoking and drinking.
MTHFR polymorphisms, folate and breast cancer
C-M Gao et al
Journal of Human Genetics
In this study, we found the total amount of dietary intake of folate to
be inversely associated with risk of breast cancer, that is, the ORs were
increasing along with decreasing folate intake among MTHFR677 C/C
and C/T genotypes. We also noted that groups with the MTHFR677
T/T genotype showed elevated ORs or breast cancer regardless of
high or low folate intake (Table 4). The protective effect of folate in
breast carcinogenesis might be dependent on MTHFR genotypes. In a
nested case–control study, Ericson et al.39found that high folate
intake increases the risk of breast cancer among women with
MTHFR677CT/TT-1298AA, whereas it tends to decrease the risk in
compound heterozygous (677CT-1298AC) women. Our similar
findings imply that folate might be involved in the development
of breast cancer, but its mechanism is incomprehensive from the
Several studies have indicated links between the MTHFR 677TT
genotype and decreased plasma folate, increased plasma homocysteine
and a low DNA uracil content.40,41The accumulation of uracil in
DNA can induce mutagenic lesions, including chromosome breaks.
Chou et al.42reported that elevated plasma homocysteine levels may
be significantly linked to increased risk of breast cancer (adjusted OR:
2.89, 95% CI: 1.70–4.92 for the highest tertile compared with the
lowest tertile). Therefore, MTHFR C677T may modulate the risk of
breast carcinogenesis. However, the data are not all consistent. Several
studies have in fact reported that the MTHFR1298CC genotype is
associated with a reduced risk of developing breast cancer.24,43Chou
et al.35observed a significantly reduced risk associated with the
compound low-activity MTHFR genotypes and the reduction was
stronger among women with low plasma folate levels. They argued
that the reduced risk might perhaps be due to increasing 5, 10-
methylene-THF levels for DNA synthesis. In this study, we observed
an increased risk of breast cancer associated with low folate intake in
individuals with 1298 A/A genotypes (Table 4). Chen et al.24and Ergul
et al.27reported earlier that T677T/A1298A showed an increased risk
for breast cancer. In the Shanghai breast cancer study, elevated ORs
were associated with folate intake in the 1298AA group (P¼0.006).38
These findings may be attributed to the 1298C allele having limited
functionality or high linkage with the 677C low-risk allele.24
Two reviews indicated that folate may have dual modulatory effects
on the development and progression of cancer depending on the
intervention timing and dose.34,44High folate intake (mainly from
folic acid supplementation) could indeed be harmful. Stolzenberg-
Solomon et al.45reported that although food folate intake was not
significantly related to breast cancer risk, total folate intake, mainly
from folic acid supplementation, significantly increased breast cancer
risk by 32%. We observed an increased risk of breast cancer associated
with the 677 TT genotype among those with high folate intake (OR:
2.41, 95% CI: 1.22–4.74). It is likely that the less active MTHFR 677
enzyme and high folate intake cause an elevated folate status. Therefore,
the role of folate metabolism in breast carcinogenesis is highly complex.
Finally, some limitations require discussion. The main results
obtained in this study could also be affected by sources of selection
bias that commonly emerged in case–control studies. There are 40
ethnic subgroups in the Jiangsu population of China, although the
Han nationality accounts for 99.82% of the total population, and
variation of ethnic subgroups in the participants of this study was not
regulated. However, the allele and genotype frequencies of the two
MTHFR loci among our controls seemed consistent with those
derived from the Hardy–Weinberg equilibrium. In our study, the
T-allele frequency in MTHFR C677T is 0.38, and the C-allele
frequency in MTHFR A1298C is 0.17 in the control group. The
statistical powers were 95.3% (OR¼1.5) and 100% (OR¼2.0) for
C677T, and 80.8% (OR¼1.5) and 99.9% (OR¼2) for A1298C. The
genotyping method of PCR–RFLP (restrictrion fragment length poly-
morphism) and the lack of a-error adjustment for multiple factors
analysis might generate some potential limitations, and therefore the
interpretation of this finding needs caution.
Table 4 Joint associations of the MTHFR genotype and folate intake with breast cancer risk
Folate intake T1 (high) T2 T3 (low)
Genotype Case/cont.ORa(CI)Case/cont. ORa(CI)Case/cont. ORa(CI)Pfor trend
Abbreviations: BMI, body mass index; CI, confidence interval; cont, control; MTHFR, 5,10-methylenetetrahydrofolate reductase; OR, odds ratio.
aORs were adjusted for age, BMI, income, menopausal status, work intensity and status of smoking and drinking.
MTHFR polymorphisms, folate and breast cancer
C-M Gao et al
Journal of Human Genetics
In summary, this study showed a relevance of folate metabolism to
breast cancer susceptibility among the Chinese female population of
the Jiangsu province. Thus, the results add support to the literature
pointing to a role of folate metabolism in carcinogenesis of the breast.
However, further studies are needed for confirmation.
This study was supported in part by a Grant-in-Aid for International Scientific
Research, Special Cancer Research from the Ministry of Education, Science,
Sports, Culture and Technology of Japan, No. 11137311, and the Major
Research Projects Foundation for Society Development from the Department
of Science and Technology of Jiangsu Province of China, No. BS2006006.
The authors thank the staff of the Public Health Centers of Taixing, Wuxi,
Jintan and Huian cities for their assistance in data collection.
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