RT Journal Article SR Electronic T1 Mononucleotide microsatellite instability and germlineMSH6 mutation analysis in early onset colorectal cancer JF Journal of Medical Genetics JO J Med Genet FD BMJ Publishing Group Ltd SP 678 OP 682 DO 10.1136/jmg.36.9.678 VO 36 IS 9 A1 Loveena Verma A1 Michael F Kane A1 Cecilia Brassett A1 James Schmeits A1 D Gareth R Evans A1 Richard D Kolodner A1 Eamonn R Maher YR 1999 UL http://jmg.bmj.com/content/36/9/678.abstract AB Germline mutations in the MSH2 andMLH1 mismatch repair genes account for most cases of hereditary non-polyposis colon cancer syndrome (HNPCC). In addition, germline MSH2 andMLH1 mutations have been detected in patients with non-HNPCC early onset colorectal cancer. GermlineMSH6 mutations appear to be rare in classical HNPCC families, but their frequency in young colorectal cancer cases has not been studied previously. In a population based study of early onset colorectal cancer (<50 years) investigated for tumour microsatellite instability (MSI), we identified a subgroup of tumours with MSI for mono- but not dinucleotide repeat markers (m-MSI+ group). In contrast to tumours with classical MSI for dinucleotide markers (d-MSI+), the m-MSI+ group cancers were mainly left sided (6/7). As MSH6 mutations in yeast and human cell lines are associated with weak (and preferential mononucleotide) MSI, the complete MSH6 gene coding region was sequenced in blood DNA from the five m-MSI+ cases available for analysis. A germline nonsense mutation was identified in an isolated case of early onset colorectal cancer (age 43 years). These results support previous findings that germline MSH6mutations may not be associated with classical MSI and suggest a role for germline MSH6 mutations in isolated early onset colorectal cancer.