title: Frequency of defective DNA mismatch repair in colorectal cancer among the Alaska Native people.
abstract: The frequency of colorectal cancer (CRC) among the Alaska Native people is the highest of any ethnic group in the United States. In this study, CRC from 329 Alaska Native people (165 Eskimo, 111 Indians, and 53 Aleut) were evaluated for evidence of defective DNA mismatch repair (MMR) by testing tumors for altered protein expression (hMLH1, hMSH2, and hMSH6) and for the presence of microsatellite instability. Of the 329 samples tested, 46 (14%) showed both microsatellite instability and altered protein expression; 42 (91%) with a loss of hMLH1, 3 (7%) hMSH2, and 1 (2%) hMLH1/hMSH6. Tumors with loss of hMLH1 were further evaluated for hMLH1 promoter hypermethylation and for the presence of the BRAF-V600E mutation. Among cases tested, all 19 (100%) tumors among the Eskimo patients showed hMLH1 promoter hypermethylation, whereas this was the case for only 3 of the 7 (42%) tumors among the Aleut (P=0.002) and 5 of the 10 (50%) tumors from the Indians (P=0.002). The majority of hypermethylated cases (23 of 27) tested positive for the V600E alteration. Of the nine tumors from the Aleut and Indian patients that did not exhibit hMLH1 hypermethylation, eight tested negative for V600E. Overall, the frequency of defective MMR among the three groups was not statistically different (P=0.75). However, the data suggest that the pathogenesis of CRC may differ between the three groups. The CRC with defective MMR among the Eskimo sample fit the typical profile for hMLH1-related cancer associated with sporadic CRC, whereas the pattern in the Aleut and Indian suggests the possibility that germ line hMLH1 mutations may be present.
authors.affiliation: Division of Gastroenterology, Mayo Clinic College of Medicine, Minnesota 55905, USA.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Boardman
authors.forename: Anne P
authors.initials: AP
authors.lastname: Lanier
authors.forename: Amy J
authors.initials: AJ
authors.lastname: French
authors.forename: Karen V
authors.initials: KV
authors.lastname: Schowalter
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Burgart
authors.forename: Kathryn R
authors.initials: KR
authors.lastname: Koller
authors.forename: Shannon K
authors.initials: SK
authors.lastname: McDonnell
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Schaid
authors.forename: Stephen N
authors.initials: SN
authors.lastname: Thibodeau
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics; D000368:Aged; D000369:Aged, 80 and over; D000413:Alaska; D015179:Colorectal Neoplasms / Q000208:ethnology / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation; D053843:DNA Mismatch Repair; D005260:Female; D018095:Germ-Line Mutation; D006801:Humans; D004930:Inuit / Q000235:genetics*; D008297:Male; D053842:Microsatellite Instability; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000235:genetics; D009367:Neoplasm Staging; D009687:Nuclear Proteins / Q000235:genetics; D011401:Promoter Regions, Genetic; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D012737:Sex Factors
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C501486:MLH1 protein, human; D009687:Nuclear Proteins; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein