High frequency of exon deletions and putative founder effects in French Canadian Lynch syndrome families.

Lynch syndrome is one of the most common autosomal dominantly inherited cancer syndromes. Mutations in MLH1, MSH2, MSH6, and PMS2 account for greater than 98% of reported mutations in Lynch syndrome families. It has been reported that large genomic deletions in MLH1 and MSH2 are a frequent cause of Lynch syndrome in certain populations. Using a multimodal approach, we have identified mutations in MLH1, MSH2, and MSH6 in French Canadian families fulfilling the Amsterdam criteria for Lynch syndrome and who displayed abnormal staining for at least one of the Lynch syndrome proteins. Mutations were identified in 28 of our 29 French Canadian probands (97%). A total of 18 distinct mutations (nine in MLH1, seven in MSH2, two in MSH6) were identified, of which six (33%) were genomic exon deletions. Another four (22%) resulted in exon deletions in cDNA alone. Three (17%) are novel mutations. Five of these 18 mutations were detected in more than one distinct family (four in MLH1, one in MSH2) and haplotype analysis suggests the possibility of founder effects. Fifteen of the 29 (52%) families carried one of these five putative founder mutations. These findings may simplify genetic testing for Lynch syndrome in French Canadians.

The value of multi-modal gene screening in HNPCC in Quebec: three mutations in mismatch repair genes that would have not been correctly identified by genomic DNA sequencing alone.

Hereditary non-polyposis colorectal cancer (HNPCC) is a dominantly inherited cancer syndrome caused by a mutation in one of the mismatch repair genes, most frequently MLH1 or MSH2. The rate of mutation detection is influenced by many factors, including the diagnostic methods used. Large deletions, which occur frequently in MLH1 and MSH2, are not detected by exon-by-exon screening methods. Here, we describe three mutations in mismatch repair genes detected using a screening protocol that combines protein truncation test (PTT) analysis and multiplex ligation-dependent probe amplification (MLPA) with genomic and cDNA sequencing. Two of these mutations consist of large deletions in MLH1 that were detected by both MLPA and PTT but that would have been missed by genomic DNA sequencing. The third is a large deletion in MSH2 that could not be detected by PTT because of its location relative to the primers used to amplify the cDNA, or by sequencing. This mutation was detected by MLPA.

Invasive breast cancer following bilateral subcutaneous mastectomy in a BRCA2 mutation carrier: a case report and review of the literature.

BACKGROUND: Primary prevention of breast cancer through prophylactic mastectomy can reduce the risk of malignancy in high-risk individuals. No type of mastectomy completely removes all breast tissue, but a subcutaneous mastectomy leaves more tissue in situ than does a simple mastectomy. CASE PRESENTATION: We report a case of invasive breast cancer in a BRCA2-positive woman 33 years after bilateral subcutaneous mastectomy. To our knowledge, only one case of primary breast cancer after prophylactic mastectomy in a BRCA1-positive patient has been reported in the literature and none in BRCA2-positive individuals. CONCLUSION: Careful documentation and long follow-up is essential to fully assess the benefits and risks of preventive surgical procedures in BRCA1 and BRCA2 mutation carriers.

A survey of APC mutations in Quebec.

This is an 11-year survey of molecular analysis of APC germline mutations for the province of Quebec done at the Molecular Pathology Unit of the Jewish General Hospital which offers genetic testing for hereditary forms of colorectal cancer for the whole of Quebec province. We report on 47 unique mutations seen in 66 families affected with familial adenomatous polyposis. Of these unique mutations, 60% are short indels, 28% are point mutations, and 6% are whole exon deletions. The absence of founder mutations and the variety of mutations encountered reinforce the value of RNA-based testing and the need for gene dosage techniques such as multiplex ligation-dependent probe amplification.