Germline mutations of the hMLH1 and hMSH2 mismatch repair genes in Belgian hereditary nonpolyposis colon cancer (HNPCC) patients.
BACKGROUND
Hereditary nonpolyposis colon cancer (HNPCC-Lynch syndrome) is caused by mutations in genes involved in DNA mismatch repair (MMR), mostly in the hMLH1 and hMSH2 genes. The mutation spectrum in the Belgian population is still poorly documented.


OBJECTIVE
To report our experience on the mutation screening in Belgian familial colorectal cancer (CRC) patients, including the investigation of the pathogenicity of the missense and splice mutations. To increase the mutation detection rate by selecting the target population.


METHODS
Two hundred and twenty five Belgian patients with familial clustering of CRC were genetically tested. Point mutations in the hMLH1 and hMSH2 genes were screened by denaturing gradient gel electrophoresis (DGGE) followed by direct sequencing. Genomic deletions and duplications were assessed by multiplex ligase dependent probe amplification (MLPA) and multiplex PCR. Missense mutations were examined for pathogenicity by means of cosegregation of the mutation with the disease, microsatellite instability (MSI) in tumors, immunohistochemical staining of tumors and determination of the population frequency of the particular mutation.


RESULTS
Twenty five pathogenic mutations were identified from which 16 were novel: 7 frameshifts, one in frame deletion, 5 genomic deletions, 5 splice defects, 4 nonsense (stop) mutations and 3 missense mutations which were classified as pathogenic (out of 10 missense mutations). In retrospect, a mutation detection rate of 71% was obtained if MSI was used as a supplementary selection criterion in addition to familial clustering.


CONCLUSIONS
Different types of pathogenic mutations in the hMLH1 and hMSH2 genes were identified in a Belgian CRC group with familial clustering. The mutation detection yield drastically increased by preliminar selection of those familial CRC patients with a microsatellite instable tumor. Considerable attention went to the assessment of the pathogenicity of the missense mutations. In practice, the cosegregation with the disease was the most relevant criterion.
Spaepen
M
M
Center for Human Genetics, University Hospital of Leuven, Leuven, Belgium.
Vankeirsbilck
B
B
Van Opstal
S
S
Tejpar
S
S
Van Cutsem
E
E
Geboes
K
K
Legius
E
E
Matthijs
G
G
D048868:Adaptor Proteins, Signal Transducing; D020137:Base Pair Mismatch / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics*; D018389:Codon, Nonsense; D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000235:genetics*; D004260:DNA Repair / Q000235:genetics; D016368:Frameshift Mutation; D017353:Gene Deletion; D018095:Germ-Line Mutation; D006801:Humans; D018895:Microsatellite Repeats; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000235:genetics*; D020125:Mutation, Missense; D009687:Nuclear Proteins / Q000235:genetics*
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018389:Codon, Nonsense; C501486:MLH1 protein, human; D009687:Nuclear Proteins; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein