title: Investigating the potential role of genetic and epigenetic variation of DNA methyltransferase genes in hyperplastic polyposis syndrome.
abstract: BACKGROUND
  Hyperplastic Polyposis Syndrome (HPS) is a condition associated with multiple serrated polyps, and an increased risk of colorectal cancer (CRC). At least half of CRCs arising in HPS show a CpG island methylator phenotype (CIMP), potentially linked to aberrant DNA methyltransferase (DNMT) activity. CIMP is associated with methylation of tumor suppressor genes including regulators of DNA mismatch repair (such as MLH1, MGMT), and negative regulators of Wnt signaling (such as WIF1). In this study, we investigated the potential for interaction of genetic and epigenetic variation in DNMT genes, in the aetiology of HPS.
  
  
  METHODS
  We utilized high resolution melting (HRM) analysis to screen 45 cases with HPS for novel sequence variants in DNMT1, DNMT3A, DNMT3B, and DNMT3L. 21 polyps from 13 patients were screened for BRAF and KRAS mutations, with assessment of promoter methylation in the DNMT1, DNMT3A, DNMT3B, DNMT3L MLH1, MGMT, and WIF1 gene promoters.
  
  
  RESULTS
  No pathologic germline mutations were observed in any DNA-methyltransferase gene. However, the T allele of rs62106244 (intron 10 of DNMT1 gene) was over-represented in cases with HPS (p<0.01) compared with population controls. The DNMT1, DNMT3A and DNMT3B promoters were unmethylated in all instances. Interestingly, the DNMT3L promoter showed low levels of methylation in polyps and normal colonic mucosa relative to matched disease free cells with methylation level negatively correlated to expression level in normal colonic tissue. DNMT3L promoter hypomethylation was more often found in polyps harbouring KRAS mutations (p = 0.0053). BRAF mutations were common (11 out of 21 polyps), whilst KRAS mutations were identified in 4 of 21 polyps.
  
  
  CONCLUSIONS
  Genetic or epigenetic alterations in DNMT genes do not appear to be associated with HPS, but further investigation of genetic variation at rs62106244 is justified given the high frequency of the minor allele in this case series.
authors.affiliation: Colorectal Medicine and Genetics, Royal Melbourne Hospital, Department of Medicine, University of Melbourne, Parkville, Victoria, Australia. musa.drini@act.gov.au
authors.forename: Musa
authors.initials: M
authors.lastname: Drini
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Wong
authors.forename: Hamish S
authors.initials: HS
authors.lastname: Scott
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Craig
authors.forename: Alexander
authors.initials: A
authors.lastname: Dobrovic
authors.forename: Chelsee A
authors.initials: CA
authors.lastname: Hewitt
authors.forename: Christofer
authors.initials: C
authors.lastname: Dow
authors.forename: Joanne P
authors.initials: JP
authors.lastname: Young
authors.forename: Mark A
authors.initials: MA
authors.lastname: Jenkins
authors.forename: Richard
authors.initials: R
authors.lastname: Saffery
authors.forename: Finlay A
authors.initials: FA
authors.lastname: Macrae
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015179:Colorectal Neoplasms / Q000235:genetics; D018899:CpG Islands / Q000235:genetics; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics*; D019175:DNA Methylation / Q000235:genetics; D044127:Epigenesis, Genetic; D005091:Exons / Q000235:genetics; D005260:Female; D006801:Humans; D044483:Intestinal Polyposis / Q000201:enzymology* / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009154:Mutation; D009691:Nucleic Acid Denaturation; D011401:Promoter Regions, Genetic / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D044366:Transition Temperature; D018631:ras Proteins / Q000235:genetics
chemical_list: C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D004248:DNA (Cytosine-5-)-Methyltransferases; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins