Efficiency of the revised Bethesda guidelines (2003) for the detection of mutations in mismatch repair genes in Austrian HNPCC patients.

The clinical diagnosis of hereditary nonpolyposis colorectal cancer (HNPCC) is based on the Amsterdam II criteria (ACII). The purpose of using the Bethesda guidelines (BG) is to select tumours for microsatellite analysis. Recently, the modified Amsterdam criteria (ACmod) and Bethesda guidelines (BGmod) were proposed to simplify definitions. We evaluated the efficiency of the ACmod and BGmod to identify patients with germ-line mutations in MLH1 and MSH2 in 81 unrelated Austrian HNPCC families. Microsatellite (MS) analysis was performed in 55 tumours. The new criteria included more families than the old ones: BGmod, n = 81; BG, n = 72; ACmod, n = 52 and ACII, n = 35. The more stringent old criteria tended to show greater positive predictive value for association with a germ-line mutation than the corresponding new criteria: BGmod, 23%; BG, 26%; ACmod, 31% and ACII, 37%. The larger number of patients analysed in the ACmod group resulted in greater sensitivity compared to the ACII. The increased workload for BGmod was not associated with greater sensitivity. Microsatellite instability (MSI) significantly enhanced specificity in all subgroups. We recommend the use of the ACmod criteria to select patients for primary sequence analysis, when microsatellite analysis is not possible. If the BG are used, we suggest that BG be given preference over BGmod, as the former signify a lesser workload.

Spectrum of germ-line MLH1 and MSH2 mutations in Austrian patients with hereditary nonpolyposis colorectal cancer.

BACKGROUND: Germ-line mutations in mismatch repair genes are associated with the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome, which is characterized by susceptibility to cancer of the colon, endometrium, small bowel or urothelium at an unusually young age and with a high degree of penetration in all generations. MATERIAL AND METHODS: One hundred and nine individuals from 46 Austrian families who fulfilled the Amsterdam criteria (n = 29) or at least one of the Bethesda guidelines (n = 17) were analyzed for mutations in MLH1 and MSH2. Microsatellite instability was determined in the tumors of index persons and affected relatives. RESULTS AND CONCLUSION: High-grade instability was present in 60.6% of the tumor samples from index patients. Twenty-three germ-line DNA sequence variants in 24/46 families and four somatic mutations in three tumors were detected in MLH1 and MSH2. Fifteen mutations are novel. None of the newly identified germ-line variants was found in 100 alleles of healthy control individuals. We were able to characterize two intronic variants (MLH1 c.589-10T>A; MSH2 c.367-1G>A) with regard to their effect on mRNA. Both created new splice sites that replaced the regular ones. Germ-line mutations occurred in 44.8% of the families fulfilling the Amsterdam criteria and in 35.3% of the Bethesda patients. The detection of a pathogenic mutation was strongly correlated with microsatellite instability in the tumor DNA (p=0.007). This study is the first comprehensive report of mutations in mismatch repair genes in Austrian patients with HNPCC.