1. ¹Department of Surgery, Kanazawa University School of Medicine, Takaramachi 13-1, Kanazawa 920-8641, Japan
2. ²Divisions of Tissue Pathology, Institute of Medical and Veterinary Science, Frome Road, Adelaide SA 5000, Australia
3. ³Molecular Pathology, Institute of Medical and Veterinary Science, Frome Road, Adelaide SA 5000, Australia
4. ⁴Colorectal Unit, Royal Adelaide Hospital, Adelaide SA 5000, Australia
5. ⁵School of Surgery and Pathology, University of Western Australia, Nedlands 6009, Australia

Correspondence: Dr B Iacopetta, E-mail: bjiac@meddent.uwa.edu.au

Received 1 September 2005; Revised 21 November 2005; Accepted 2 December 2005; Published online 17 January 2006.

Abstract

The CpG-island methylator phenotype (CIMP+) in colorectal cancer (CRC) is characterised by frequent hypermethylation of promoter regions in tumour suppressor genes. Low level methylation of some CpG islands is also seen in the normal colonic mucosa and increases with age; however, it is still unclear what other factors regulate this phenomenon. The first aim of our study was to determine whether the level of promoter methylation is elevated in the normal colonic mucosa of patients with CIMP⁺ tumours. The second aim was to investigate whether common, functional polymorphisms in genes involved in methyl group metabolism are associated with the level of methylation in this tissue. CpG islands within the ER, MYOD, P16(INK4A), MLH1, APC, P14(ARF), DAPK and TIMP3 genes were quantitatively evaluated for methylation in normal colonic mucosa from a large series of CRC patients using the MethyLight assay. Genotyping was carried out for polymorphisms in the MTHFR, TS, MS, MTHFD1 and DNMT3b genes. Methylation of ER and MYOD in normal colonic mucosa increased with age and was higher in female subjects. Methylation of P16(INK4A), MLH1, TIMP3 and DAPK in normal mucosa occurred at a lower level than ER and MYOD but also increased with age and was significantly higher in patients with CIMP⁺ tumours. The DNMT3b C46359T polymorphism was associated with significantly less methylation of MYOD and MLH1 and with trends for lower methylation in each of the other CpG islands examined. Our results demonstrate that age, gender and genetic factors can influence the methylation level of CpG islands in gene promoter regions of normal colonic mucosa. Further work is required to determine whether such methylation is associated with the development of CIMP⁺ CRC.