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5,10-Methylenetetrahydrofolate Reductase Codon 677 and 1298 Polymorphisms
and Colon Cancer in African Americans and Whites

April 24, 2003

Abstraction Template
     
Key variables & Description Article

Reference
Complete the bibliographic reference for the article according to AJE format.

 

Keku T, Millikan R, Worley K, et al. 5-10-methylenetetrahydrofolate reductase codon 677 and 1298 polymorphisms and colon cancer in African Americans and whites. Cancer Epidemiol, Biomarkers Prev 2002; 11: 1611-21.

Category of HuGE information
Specify the types of information (from the list below) available in the article:

  1. Prevalence of gene variant
  2. Gene-disease association
  3. Gene-environment interaction
  4. Gene-gene interaction
  5. Genetic test evaluation/monitoring

 

  1. Prevalence of gene variant
  2. Gene-disease association
  3. Gene-environment interaction

 

Study hypotheses or purpose
The authors study hypotheses or main purpose for conducting the study

 

To investigate the roles of single nucleotide variant polymorphisms in MTHFR codons 677 and 1298 in colon cancer among African Americans and whites to estimate the main effects of the MTHFR genotypes and their joint effects with folate intake and alcohol consumption.

Gene(s)
Identification of the following:

  1. Gene name
  2. Chromosome location
  3. Gene product/function
  4. Alleles
  5. OMIM #

 

  1. Gene: MTHFR
  2. Chromosome location:  1p36.3
  3. Gene product/function: 5-10 methylenetetrahydrofolate reductase, an enzyme that reduces 5-10 methylenetetrahydrofolate to 5-10 methylhydrofolate.
  4. Alleles:  Codon 677: C (ala), T (val) and Codon 1298: A (glu), C (ala)
  5. OMIM #: 607093

Environmental factor(s)
Identification of the major environmental factors studied (infectious, chemical, physical, nutritional, and behavioral)

 

1. Folate intake, dietary and supplement use; (2) alcohol consumption

Health outcome(s)
Identification of the major health outcome(s) studied

 

1. Colon cancer
Study design
Specification of the type of study design(s)
  1. Case-control
  2. Cohort 
  3. Cross-sectional
  4. Descriptive or case series
  5. Clinical trial
  6. Population screening

 

1. Case-control

 

Case definition
For study designs 1, 4, and 5, define the following if available:
  1. Disease case definition
  2. Exclusion criteria
  3. Gender
  4. Race/ethnicity
  5. Age
  6. Time period
  7. Geographic location
  8. Number of participants
  1. Disease case definition: First-time diagnosis of a histologically confirmed invasive adenocarcinoma of the colon, North Carolina Central Cancer Registry.
  2. Exclusion Criteria:  By permission of primary physician only; race other than black or white; nonresident of 33-county study area in North Carolina; inability to give informed consent; mental incompetence to take part in study; or lack of a North Carolina ID/drivers’ license if less than age 65 years (for comparability with controls).
  3. Gender: 289 men, 265 women (note: gender data missing for n=1 case)
  4. Race/ethnicity: 244 African Americans, 311 whites
  5. Age: 40-85 years at time of diagnosis
  6. Time period: Diagnosis confirmed from 7/1/96 through 6/30/2000
  7. Geographic location: 33-county area of central North Carolina
  8. Number of participants: 555

 

Control definition
For study design 1, define the following if available:
  1. Control selection criteria
  2. Matching variables
  3. Exclusion criteria
  4. Gender
  5. Race/ethnicity
  6. Age
  7. Time period
  8. Geographic location
  9. Number of participants
  1. Control selection criteria: Taken from prospective sample of 3391 nulliparous French Canadian pregnant women, investigated for the development of hypertensive disorder at St-François d’Assise hospital.
  2. Matching variables: maternal age (±5 years), gestational age at delivery (±1 week), body mass index (kg/m2, <20, 20-24, 25-27, and >27), and month of the year of delivery. Attempted to match 2 control subjects for every case. See Table 1.
  3. Exclusion criteria: Multiple pregnancies, preexisting secondary hyptertension, and preexisting hypertension with superimposed preeclampsia.
  4. Gender: Female
  5. Race/ethnicity: White, French Canadian descent
    Age: 27±5 (for controls matched for Chronic Essential hypertension), 26±5 (for controls matched for preeclampsia)
  6. Time period: 1996-2000
  7. Geographic Location: St-François d’Assise hospital in Quebec City , Canada
  8. Number of participants: 357 controls for Chronic Essential Hypertension case group (10.5% of original prospective study) and 310 controls for Preeclampsia case group (9.76% of original prospective study).

 

Assessment of environment factors
For studies that include gene-environment interactions, define the following, if available:
  1. Environmental factor
  2. Exposure assessment
  3. Exposure definition
  4. Number of participants with exposure data (% of total eligible)

 

  1. Environmental factor: Folate intake
  2. Exposure assessment:The sum of results to NCI Food Frequency questionnaire with NCI nutrient analysis (including 10 questions for specific North Carolina foods) and a yes/no assessment of vitamin supplement use.
  3. Exposure definition: Less than 400 ug of folate per day, nonuse of a folate-containing supplement (vitamin).
  4. Number of participants with exposure data: 639 (99.4%) cases, 1048 (99.9%) controls
Genotyping
Specify the following:
  1. Gene
  2. DNA source
  3. Methodology
  4. Number of participants genotyped (% of total eligible) 

 

  1. Gene: MTHFR, codons 677 and 1298
  2. DNA source: Blood samples
  3. Methodology: Isolated from blood by Pure-Gene isolation kits, analyzed by PCR-RFLP and Taqman assay.
  4. Number of participants genotyped: 552 (85.8%) cases, 868 (82.7%) controls

 

Results
Describe the major results under each of the following HuGE categories. Include tables when data are provided:
  1. Prevalence of gene variant
  2. Gene-disease association
  3. Gene-environment interaction
  4. Gene-gene interaction
  5. Genetic test evaluation/monitoring

Prevalence of gene variant: MTHFR 677 C(ala)->T(val): African American controls; CC(80.2%), CT(17.9%), TT(1.8%); white controls, CC(49.2%), CT(41.4%), TT(9.4%).
MTHFR 1298 A(glu)->C(ala): African American controls, AA(66.0%), AC(30.0%), CC(4.0%); white controls, AA(43.8%), AC(43.6%), CC(12.6%).

Gene-disease association: No association was found between the reduced-activity MTHFR codon 677 TT genotype and colon cancer in either African Americans or whites. A slight protective effect was noted in whites for the reduced-activity MTHFR codon 1298 CC genotype (Table 1a). Significant inverse associations with colon cancer were found for whites who had the combined genotypes of 1298 CC + 677 CC (Table 1b).

Gene-environment interaction: When total daily folate intake was less than 400 ug, a positive association existed for 677 CC + CT normal and heterozygous genotypes (versus TT) and colon cancer in both races adjusted for age, gender and race, and for 677 CC normal (versus CT + TT). In whites a positive association existed for 677 CT + TT (versus CC), adjusted for age and gender, in the presence of low folate intake. When no dietary supplement was used, a significant positive association in whites existed only for 677 CC + CT and TT + CT (Table 2).

Genotypes 1298 AA + AC (versus CC) and for 1298 AA (versus CC + AC) in both races, where daily folate intake was less than 400 ug, were more likely to have colon cancer. In whites, a positive association existed between 1298 AA + AC (versus CC) and for 1298 AA (versus CC + AC) in the presence of no dietary supplement use (Table 2).

The authors did not detect any interaction between low folate intake and alcohol consumption. They found an inverse relation between colorectal cancer and never-drinkers with genotype 1298 CC, but this finding was significant only for whites (Table 3).

 

Conclusion
State the author's overall conclusions from the study

Addressing biologic plausibility, Keku et al. (2002) suggest that normal MTHFR enzymatic activity in conjunction with low daily folate intake increases colon cancer risk because the reaction catalyzed by MTHFR leaves less of the 5-10-MTHF substrate available for improved DNA synthesis. They support this theory with findings that, among the low folate intake group, subjects with the normal allele were sometimes more likely to have colon cancer.

However, the authors did not find a significant inverse association between MTHFR 677 TT reduced-activity genotype and colon cancer. They indeed found an inverse association between MTHFR 1298 CC reduced-activity genotype versus the AA + AC genotype, but only in whites. They suggest this may implicate the 1298 codon more strongly than the 677 codon in colon cancer, unlike other studies (see below).

The authors explain that their findings may be inconsistent with others because daily folate exposure for the controls in their North Carolina study was lower than that of a representative sample of all U.S. citizens in 1994-1996. They assert that in low-folate intake populations, a protective effect of low-activity MTHFR is more difficult to detect.
Comments
Provide additional insight, including methodologic issues and/or concerns about the study

Keku et al. address a number of limitations in their study. They note a tendency for food frequency questionnaires to underreport folate intake. On the other hand, they may have overestimated folate intake in some participants by assuming that all dietary supplement tablets contain 400 ug of folate. To test this problem, they assumed lower values for the folate supplement tablets and found that their results did not change. Additionally, they mention that recall bias must be factored into these limitations because the questionnaires were administered post-diagnosis.

The authors argue that the effect of the polymorphisms may differ by tumor stage. They argue that the odds ratios they calculated for proximal tumors and the 677 TT genotype were more inverse than for distal tumors for both races. However, the ORs they calculated were not significant based on 95% confidence limits and data on tumor stage are not provided.

Overall, the literature is inconsistent regarding the association between MTHFR polymorphisms and colon cancer. Ryan et al. (2001) found that 677 CT heterozygotes were significantly more likely to have colorectal cancer (OR: 1.86, 95% CI: 1.3, 2.7). The study also determined that the mutant “T” allele was more frequent in the cases (p<0.008). Chen et al. (2002) conducted a nested case-control study of incident colorectal cancer cases among the prospective Physician’s Health Study cohort. First, they noted that C677T and A1298C were in linkage disequilibrium. Second, there was a non-significant inverse association with disease for the unusual 1298 CC genotype (OR: 0.73, 95% CI: 0.37-1.43). They concluded that A1298C was a less important independent risk factor than C667T. Delgado-Enciso et al. (2001) found a detrimental effect for normal and heterozygous genotypes 677 TT and CT versus CC (OR: 1.81, CI:0.97-3.3). They concluded, however, that a positive association existed between the mutated allele and colon cancer. Finally, a case-control study by

Ulrich et al. (2000) that stratified subjects by folate intake found no association between the C677T MTHFR polymorphism and colorectal cancer. Interestingly, their study did find a positive association between alcohol consumption and hyperplastic colorectal polyps, regardless of 677 MTHFR genotype.

From the findings in the present study, MTHFR does not appear to be strongly implicated in colon cancer. However, it confirms the importance of adequate folate intake in the reduction of colorectal cancer risk. Future studies may be of interest in different populations to help clarify the interaction of MTHFR and folate.

 

Supplementary Tables

Table 1a. ORs and 95% CI for colon cancer in relation to MTHFR codon 677 and 1298  

Table 1b. ORs* and 95% CI for combined MTHFR codon 677 and 1298 genotypes among African Americans and whites

Table 2. ORs and 95% CI for colon cancer, in relation to codons 677 and 1298, and folate intake, measured in micrograms per day, and use of a dietary supplement (vitamin tablet containing folate).

Table 3. ORs for colon cancer in relation to MTHFR codon 677 and 1298, and alcohol intake.

 

Last Updated August 23, 2004