title: Functional characterization of rare missense mutations in MLH1 and MSH2 identified in Danish colorectal cancer patients.
abstract: Recently, we have performed a population based study to analyse the frequency of colorectal cancer related MLH1 and MSH2 missense mutations in the Danish population. Half of the analyzed mutations were rare and most likely only present in the families where they were identified originally. Some of the missense mutations were located in conserved regions in the MLH1 and MSH2 proteins indicating a relation to disease development. In the present study, we functionally characterized 10 rare missense mutations in MLH1 and MSH2 identified in 13 Danish CRC families. To elucidate the pathogenicity of the missense mutations, we carried out in vitro functional analyses. The missense mutations were analyzed for their effect on protein expression and repair efficiency. The results of the functional analysis were correlated with clinical data on the families carrying these mutations. Eight missense mutations resulted in proteins with expression and repair efficiency similar to the wild type. One missense mutation (MSH2 p.Met688Val) caused reduced protein expression and one (MSH2 p.Leu187Arg) caused both reduced protein expression and repair deficiency. The MSH2 p.Leu187Arg mutation was found in an Amsterdam II family presenting with high microsatellite instability and loss of MSH2 and MSH6 proteins in tumours. In conclusion, only 1/10 missense mutations displayed repair deficiency and could be classified as pathogenic. No final conclusion can be drawn on the MSH2 p.Met688Val mutation, which caused reduced protein expression. Although, no deficiencies have been identified in the proteins harbouring the other missense mutations, pathogenicity of these variants cannot be unambiguously excluded.
authors.affiliation: Molecular Diagnostic Laboratory, Aarhus University Hospital, Skejby, Denmark. liselotte.christensen@ki.au.dk
authors.forename: Lise Lotte
authors.initials: LL
authors.lastname: Christensen
authors.forename: Reetta
authors.initials: R
authors.lastname: Kariola
authors.forename: Mari K
authors.initials: MK
authors.lastname: Korhonen
authors.forename: Friedrik P
authors.initials: FP
authors.lastname: Wikman
authors.forename: Lone
authors.initials: L
authors.lastname: Sunde
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Gerdes
authors.forename: Henrik
authors.initials: H
authors.lastname: Okkels
authors.forename: Carsten A
authors.initials: CA
authors.lastname: Brandt
authors.forename: Inge
authors.initials: I
authors.lastname: Bernstein
authors.forename: Thomas V O
authors.initials: TV
authors.lastname: Hansen
authors.forename: Rikke
authors.initials: R
authors.lastname: Hagemann-Madsen
authors.forename: Claus L
authors.initials: CL
authors.lastname: Andersen
authors.forename: Minna
authors.initials: M
authors.lastname: Nyström
authors.forename: Torben F
authors.initials: TF
authors.lastname: Ørntoft
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000328:Adult; D015153:Blotting, Western; D015179:Colorectal Neoplasms / Q000235:genetics*; D003718:Denmark; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000235:genetics*; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D009687:Nuclear Proteins / Q000235:genetics*; D010375:Pedigree
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C501486:MLH1 protein, human; D009687:Nuclear Proteins; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein
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