title: The methylenetetrahydrofolate reductase (MTHFR) gene in colorectal cancer: role in tumor development and significance of allelic loss in tumor progression.
abstract: OBJECTIVE
  Folate deficiency predisposes to sporadic colorectal cancer (CRC). Methylenetetrahydrofolate reductase (MTHFR) is a critical folate-metabolising enzyme and a polymorphism at position 677 (C677T), is associated with reduced enzyme activity. We investigated whether this functional polymorphism modulates the risk of developing CRC.
  
  
  METHODS
  This was a retrospective case-control study. 136 unselected cases of sporadic CRC and 848 normal population controls were genotyped for the MTHFR C677T polymorphism. Tumor tissue was genotyped to assess loss of heterozygosity (LOH).
  
  
  RESULTS
  MTHFR CT heterozygotes had a significantly increased risk of developing CRC (53.7% of CRC cases vs 38.4% of controls), odds ratio 1.86 (95% CI 1.3-2.7, p < 0.005). No increased cancer risk was observed in TT homozygotes. The MTHFR 'T' allele frequency was significantly higher in the cancer group (0.3713) as compared to controls (0.2900, p < 0.008). LOH at the MTHFR locus was observed in 18% of informative cancers, with exclusive loss of the variant 'T' allele, in all cases.
  
  
  CONCLUSIONS
  In this study of a homogenous northern European population, MTHFR CT heterozygotes had an almost two-fold increased risk of developing sporadic CRC. The exclusive pattern of MTHFR allele loss in cases of LOH, suggest that functional MTHFR activity within a tumor might play an important role in the survival and progression of a colonic neoplasm.
authors.affiliation: Department of Gastroenterology and Clinical Medicine, St. James's Hospital and Trinity College, Dublin, Ireland. bbryan@planet.nl
authors.forename: B M
authors.initials: BM
authors.lastname: Ryan
authors.forename: A M
authors.initials: AM
authors.lastname: Molloy
authors.forename: R
authors.initials: R
authors.lastname: McManus
authors.forename: Q
authors.initials: Q
authors.lastname: Arfin
authors.forename: D
authors.initials: D
authors.lastname: Kelleher
authors.forename: J M
authors.initials: JM
authors.lastname: Scott
authors.forename: D G
authors.initials: DG
authors.lastname: Weir
mesh_terms: D000230:Adenocarcinoma / Q000201:enzymology / Q000235:genetics*; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000201:enzymology / Q000235:genetics*; D018450:Disease Progression; D006801:Humans; D019656:Loss of Heterozygosity; D042965:Methylenetetrahydrofolate Reductase (NADPH2); D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000235:genetics*; D011110:Polymorphism, Genetic / Q000235:genetics; D012189:Retrospective Studies; D012307:Risk Factors
chemical_list: D000587:Oxidoreductases Acting on CH-NH Group Donors; D042965:Methylenetetrahydrofolate Reductase (NADPH2)