Clustering of Lynch syndrome malignancies with no evidence for a role of DNA mismatch repair.

OBJECTIVES: We ascertained a large kindred with an excess of Lynch syndrome-associated cancers. Our objective was to determine if a defect in one of the DNA mismatch repair (DMMR) genes was the probable cause of cancer susceptibility as microsatellite instability (MSI) and immunohistochemical (IHC) analysis of the probands' tumors did not provide a clear indication.

METHODS: A detailed history and review of medical records was undertaken to construct a four-generation pedigree. Blood samples were obtained for analysis of germline DNA. Polymorphic repeats from the MLH1, MSH2, MSH6, and PMS2 loci were genotyped and the co-segregation of markers and disease was assessed. DMMR gene expression for all available tumors was evaluated by IHC. Combined bisulfite restriction analysis (COBRA) of MLH1 was utilized to test for germline epimutation.

RESULTS: Four gynecologic carcinomas, 3 colon carcinomas, and 13 cases of adenomatous polyps were identified. The family met Amsterdam II criteria. The mean age of cancer diagnosis in the kindred was 63 years (range 44-82 years). DNA marker analyses excluded linkage to MLH1, MSH2, MSH6, and PMS2. Furthermore, MSI and IHC analysis of tumors did not suggest a role for DMMR. Methylation of the MLH1 promoter was identified in the peripheral blood leukocytes (PBLs) of a family member with an early onset colon cancer.

CONCLUSIONS: We identified a large family with multiple Lynch malignancies and no evidence for an inherited defect in DMMR. This family represents an important but poorly understood form of autosomal dominant inherited cancer susceptibility. Aberrant MLH1 promoter methylation in normal tissues may be a marker for cancer susceptibility in families such as this.