title: Conversion analysis for mutation detection in MLH1 and MSH2 in patients with colorectal cancer.
abstract: BACKGROUND
  The accurate identification and interpretation of germline mutations in mismatch repair genes in colorectal cancer cases is critical for clinical management. Current data suggest that mismatch repair mutations are highly heterogeneous and that many mutations are not detected when conventional DNA sequencing alone is used.
  
  
  OBJECTIVE
  To evaluate the potential of conversion analysis compared with DNA sequencing alone to detect heterogeneous germline mutations in MLH1, MSH2, and MSH6 in colorectal cancer patients.
  
  
  METHODS
  Multicenter study with patients who participate in the Colon Cancer Family Registry. Mutation analyses were performed in participant samples determined to have a high probability of carrying mismatch repair germline mutations. Samples from a total of 64 hereditary nonpolyposis colorectal cancer cases, 8 hereditary nonpolyposis colorectal cancer-like cases, and 17 cases diagnosed prior to age 50 years were analyzed from June 2002 to June 2003.
  
  
  METHODS
  Classification of family members as carriers or noncarriers of germline mutations in MLH1, MSH2, or MSH6; mutation data from conversion analysis compared with genomic DNA sequencing.
  
  
  RESULTS
  Genomic DNA sequencing identified 28 likely deleterious exon mutations, 4 in-frame deletion mutations, 16 missense changes, and 22 putative splice site mutations. Conversion analysis identified all mutations detected by genomic DNA sequencing--plus an additional exon mutation, 12 large genomic deletions, and 1 exon duplication mutation--yielding an increase of 33% (14/42) in diagnostic yield of deleterious mutations. Conversion analysis also showed that 4 of 16 missense changes resulted in exon skipping in transcripts and that 17 of 22 putative splice site mutations affected splicing or mRNA transcript stability. Conversion analysis provided an increase of 56% (35/63) in the diagnostic yield of genetic testing compared with genomic DNA sequencing alone.
  
  
  CONCLUSIONS
  The data confirm the heterogeneity of mismatch repair mutations and reveal that many mutations in colorectal cancer cases would be missed using conventional genomic DNA sequencing alone. Conversion analysis substantially increases the diagnostic yield of genetic testing for mismatch repair mutations in patients diagnosed as having colorectal cancer.
authors.affiliation: Department of Cancer Biology, Cleveland Clinic Lerner College of Medicine, Cleveland, Ohio 44195, USA. caseyg@ccf.org
authors.forename: Graham
authors.initials: G
authors.lastname: Casey
authors.forename: Noralane M
authors.initials: NM
authors.lastname: Lindor
authors.forename: Nickolas
authors.initials: N
authors.lastname: Papadopoulos
authors.forename: Stephen N
authors.initials: SN
authors.lastname: Thibodeau
authors.forename: John
authors.initials: J
authors.lastname: Moskow
authors.forename: Scott
authors.initials: S
authors.lastname: Steelman
authors.forename: Carolyn H
authors.initials: CH
authors.lastname: Buzin
authors.forename: Steve S
authors.initials: SS
authors.lastname: Sommer
authors.forename: Christine E
authors.initials: CE
authors.lastname: Collins
authors.forename: Malinda
authors.initials: M
authors.lastname: Butz
authors.forename: Melyssa
authors.initials: M
authors.lastname: Aronson
authors.forename: Steven
authors.initials: S
authors.lastname: Gallinger
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Barker
authors.forename: Joanne P
authors.initials: JP
authors.lastname: Young
authors.forename: Jeremy R
authors.initials: JR
authors.lastname: Jass
authors.forename: John L
authors.initials: JL
authors.lastname: Hopper
authors.forename: Anh
authors.initials: A
authors.lastname: Diep
authors.forename: Bharati
authors.initials: B
authors.lastname: Bapat
authors.forename: Michael
authors.initials: M
authors.lastname: Salem
authors.forename: Daniela
authors.initials: D
authors.lastname: Seminara
authors.forename: Robert
authors.initials: R
authors.lastname: Haile
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D020137:Base Pair Mismatch / Q000235:genetics*; D015139:Blotting, Southern; D002352:Carrier Proteins; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000235:genetics / Q000473:pathology; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000235:genetics*; D005785:Gene Conversion; D018095:Germ-Line Mutation; D006801:Humans; D007150:Immunohistochemistry; D018895:Microsatellite Repeats; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009154:Mutation / Q000235:genetics*; D009363:Neoplasm Proteins / Q000235:genetics*; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins / Q000235:genetics*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein