Genomic rearrangements in MSH2, MLH1 or MSH6 are rare in HNPCC patients carrying point mutations.
Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant disease with high penetrance, caused by germline mutations in the mismatch repair (MMR) genes MLH1, MSH2, MSH6, PMS2 and MLH3. Most reported pathogenic mutations are point mutations, comprising single base substitutions, small insertions and deletions. In addition, genomic rearrangements, such as large deletions and duplications not detectable by PCR and Sanger sequencing, have been identified in a significant proportion of HNPCC families, which do not carry a pathogenic MMR gene point mutation. To clarify whether genomic rearrangements in MLH1, MSH2 or MSH6 also occur in patients carrying a point mutation, we subjected normal tissue DNA of 137 colorectal cancer (CRC) patients to multiplex ligation-dependent probe amplification (MLPA) analysis. Patients fulfilled the following pre-requisites: all patients met at least one criterion of the Bethesda guidelines and their tumors exhibited high microsatellite instability (MSI-H) and/or showed loss of expression of MLH1, MSH2 or MSH6 proteins. PCR amplification and Sanger sequencing of all exons of at least one MMR gene, whose protein expression had been lost in the tumor tissue, identified 52 index patients without a point mutation (Group 1), 71 index patients with a pathogenic point mutation in MLH1 (n=38) or MSH2 (n=22) or MSH6 (n=11) (Group 2) and 14 patients with an unclassified variant in MLH1 (n=9) or MSH2 (n=3) or MSH6 (n=2) (Group 3). In 13 of 52 patients of group 1 deletions of at least one exon were identified. In addition, in group 3 one EX1_15del in MLH1 was found. No genomic rearrangement was identified in group 2 patients. Genomic rearrangements represent a significant proportion of pathogenic mutations of MMR genes in HNPCC patients. However, genomic rearrangements are rare in patients carrying point mutations in MMR genes. These findings suggest the use of genomic rearrangement tests in addition to Sanger sequencing in HNPCC patients.
Pistorius
Steffen
S
Department of Visceral, Thoracic and Vascular Surgery, Technische Universität Dresden, Fetscherstr. 74, 01307 Dresden, Germany. stteffen.pistorius@uniklinikum-dresden.de
Görgens
Heike
H
Plaschke
Jens
J
Hoehl
Ruth
R
Krüger
Stefan
S
Engel
Christoph
C
Saeger
Hans-Detlev
HD
Schackert
Hans K
HK
D048868:Adaptor Proteins, Signal Transducing; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000235:genetics / Q000473:pathology*; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000235:genetics*; D017353:Gene Deletion; D006801:Humans; D008969:Molecular Sequence Data; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000235:genetics*; D009687:Nuclear Proteins / Q000235:genetics*; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D012689:Sequence Homology, Nucleic Acid
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C501486:MLH1 protein, human; D009687:Nuclear Proteins; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein