title: DNA hypermethylation appears early and shows increased frequency with dysplasia in Lynch syndrome-associated colorectal adenomas and carcinomas.
abstract: BACKGROUND
  Lynch syndrome (LS) is associated with germline mutations in DNA mismatch repair (MMR) genes. The first "hit" to inactivate one allele of the predisposing MMR gene is present in every cell, contributing to accelerated tumorigenesis. Less information is available of the nature, timing, and order of other molecular "hits" required for tumor development. To this end, MMR protein expression and coordinated promoter methylation were examined in colorectal specimens prospectively collected from LS mutation carriers (n = 55) during colonoscopy surveillance (10/2011-5/2013), supplemented with retrospective specimens.
  
  
  RESULTS
  Loss of MMR protein corresponding to the gene mutated in the germline increased with dysplasia, with frequency of 0 % in normal mucosa, 50-68 % in low-grade dysplasia adenomas, and 100 % in high-grade dysplasia adenomas and carcinomas. Promoter methylation as a putative "second hit" occurred in 1/56 (2 %) of tumors with silenced MMR protein. A general hypermethylation tendency was evaluated by two gene sets, eight CpG island methylator phenotype (CIMP) genes, and seven candidate tumor suppressor genes linked to colorectal carcinoma (CRC). Hypermethylation followed the same trend as MMR protein loss and was present in some low-grade dysplasia adenomas that still expressed MMR protein suggesting the absence of a "second hit." To assess prospectively collected normal mucosa for carcinogenic "fields," the specimen donors were stratified according to age at biopsy (50 years or below vs. above 50 years) and further according to the absence vs. presence of a (previous or concurrent) diagnosis of CRC. In mutation carriers over 50 years old, two markers from the candidate gene panel (SFRP1 and SLC5A8) revealed a significantly elevated average degree of methylation in individuals with CRC diagnosis vs. those without.
  
  
  CONCLUSIONS
  Our findings emphasize the importance and early appearance of epigenetic alterations in LS-associated tumorigenesis. The results serve early detection and assessment of progression of CRC.
authors.affiliation: Division of Genetics, Department of Biosciences, University of Helsinki, Helsinki, Finland ; Department of Medical and Clinical Genetics, University of Helsinki, Helsinki, Finland.
authors.forename: Satu
authors.initials: S
authors.lastname: Valo
authors.affiliation: Department of Medical and Clinical Genetics, University of Helsinki, Helsinki, Finland.
authors.forename: Sippy
authors.initials: S
authors.lastname: Kaur
authors.affiliation: Genome-Scale Biology, Research Programs Unit, University of Helsinki, Helsinki, Finland ; Department of Pathology, HUSLAB, Helsinki University Central Hospital and University of Helsinki, Helsinki, Finland.
authors.forename: Ari
authors.initials: A
authors.lastname: Ristimäki
authors.affiliation: Department of Gastrointestinal and General Surgery, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Laura
authors.initials: L
authors.lastname: Renkonen-Sinisalo
authors.affiliation: Department of Gastrointestinal and General Surgery, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Heikki
authors.initials: H
authors.lastname: Järvinen
authors.affiliation: Department of Surgery, Jyväskylä Central Hospital, University of Eastern Finland, Jyväskylä, Finland.
authors.forename: Jukka-Pekka
authors.initials: JP
authors.lastname: Mecklin
authors.affiliation: Division of Genetics, Department of Biosciences, University of Helsinki, Helsinki, Finland.
authors.forename: Minna
authors.initials: M
authors.lastname: Nyström
authors.affiliation: Department of Medical and Clinical Genetics, University of Helsinki, Helsinki, Finland.
authors.forename: Päivi
authors.initials: P
authors.lastname: Peltomäki
keywords: Adenoma-carcinoma sequence; Colorectal cancer; CpG island methylator phenotype; DNA methylation; Lynch syndrome; MS-MLPA