Background: Hereditary nonpolyposis colorectal cancer (HNPCC) is linked genetically to mutations in DNA mismatch repair (MMR) genes. Because a deficiency in MMR does not predict a specific phenotype, the original selection criteria may be too restrictive in identifying additional families. The current study was performed to determine whether a relaxation of the Amsterdam criteria (AC) could be applied to identify more families associated with DNA MMR.
Methods: Twenty-eight unrelated Swiss families (15 complying with the AC and 13 fulfilling extended criteria [EC] to include other tumors of the HNPCC spectrum as well) were screened for mutations in the MMR genes hMSH2 and hMLH1, using single-stranded conformation polymorphism and direct DNA sequencing. Microsatellite instability (MSI) was determined in 14 families. A comparison was made between the phenotypic characteristics of the mutation positive and mutation negative families.
Results: Ten AC families (67%) harbored germline mutations in hMLH1 (6 kindreds) or hMSH2 (4 kindreds). In none of the EC kindreds could an unambiguous disease-causing mutation be identified. Seven of eight AC families were found to display MSI whereas all colorectal carcinomas (CRC) in eight EC kindreds were MSI stable. CRC patients from mutation positive families had an earlier age at diagnosis (44 years vs. 49 years) and appeared to have a better survival (11.1 years vs. 7.7 years).
Conclusions: Extending the AC to include extracolonic tumors of the HNPCC spectrum results in a very low mutation detection rate for hMSH2 and hMLH1. The EC families appear to represent an alternative genetic entity not necessarily related to DNA MMR gene mutations because they do not display MSI.