Analysis of these 11 clinically diagnosed HNPCC cases by NCI, MNR, IHC, and PNA methods showed that two cases were determined as MSS in all four tests, indicating that these two cases can be considered as familial colorectal cancer type X. In the remaining nine cases, MSI-H was determined by all four tests and mutations in MLH1 or MSH2 were detected (data not shown), which leads us to consider the nine cases are Lynch syndrome. This evidence concerns the gene MLH1 and Lynch syndrome.