Frequency of rearrangements in Lynch syndrome cases associated with MSH2: characterization of a new deletion involving both EPCAM and the 5' part of MSH2

Lynch syndrome is caused by germline mutations in MSH2, MLH1, MSH6, and PMS2 mismatch repair genes and leads to a high risk of colorectal and endometrial cancer. It was recently shown that constitutional 3' end deletions of EPCAM could cause Lynch syndrome in tissues with MSH2 deficiency. We aim to establish the spectrum of mutations in MSH2-associated Lynch syndrome cases and their clinical implications. Probands from 159 families suspected of having Lynch syndrome were enrolled in the study. Immunohistochemistry and microsatellite instability (MSI) analyses were used on the probands of all families. Eighteen cases with MSH2 loss were identified: eight had point mutations in MSH2. In 10 Lynch syndrome families without MSH2 mutations, EPCAM-MSH2genomic rearrangement screening was carried out with the use of multiplex ligation-dependent probe amplification and reverse transcriptase PCR. We report that large germline deletions, encompassing one or more exons of the MSH2 gene, cosegregate with the Lynch syndrome phenotype in 23% (8 of 35) of MSI families tested. A new combined deletion EPCAM-MSH2 was identified and characterized by break point analysis, encompassing from the 3' end region of EPCAM to the 5' initial sequences of the MSH2 (c.859-1860_MSH2:646-254del). EPCAM-MSH2 fusion transcript was isolated. The tumors of the carriers show high-level MSI and MSH2 protein loss. The clinical correlation provided evidence that the type of mutation and the extension of the deletions involving the MSH2 gene could have different implications in cancer predisposition. Thus, the identification of EPCAM-MSH2 rearrangements and their comprehensive characterization should be included in the routine mutation screening protocols for Lynch syndrome.

Characterization of new founder Alu-mediated rearrangements in MSH2 gene associated with a Lynch syndrome phenotype

It has been reported that large genomic deletions in the MLH1 and MSH2 genes are a frequent cause of Lynch syndrome in certain populations. Here, a cohort has been screened and two new founder rearrangements have been found in the MSH2 gene. These mutations have been characterized by break point determination, haplotype analysis, and genotype-phenotype correlation. Mutations have been identified in the MLH1, MSH2, and MSH6 genes in 303 subjects from 160 suspected Lynch syndrome unrelated families. All subjects were tested using heteroduplex analysis by capillary array electrophoresis. Multiplex ligation-dependent probe amplification was used to detect rearrangements in mutation-negative index patients and confirmed by reverse transcriptase PCR. The break point of the deletions was further characterized by the array comparative genomic hybridization method. Immunohistochemical staining and microsatellite instability were studied in tumor samples. Hereditary nonpolyposis colorectal cancer-related phenotypes were evaluated. More than 16% (24 of 160) of the families had pathogenic mutations (8 MLH1, 15 MSH2, and 1 MSH6). Twelve of these families (50%) are carriers of a novel mutation. Seven of the 15 positive MSH2 families (47%) are carriers of a rearrangement. The exon 7 deletion and exon 4 to 8 deletion of MSH2 are new founder mutations. The segregation of a common haplotype, a similar phenotype, and anticipation effects were observed in these families. These findings will greatly simplify the diagnosis, counseling, and clinical care in suspected Lynch syndrome families and not just in specific geographic areas, so wide distribution may be explained by migration patterns.

Twenty-three novel BRCA1 and BRCA2 sequence alterations in breast and/or ovarian cancer families of Eastern Spain

It is well established that mutations in BRCA1 and BRCA2 genes significantly increase the risk of breast and ovarian cancer. We here report 23 novel genetic variants of the BRCA1 and BRCA2 genes found in 349 cancer-prone unrelated families from Eastern Spain detected during the first 2 years of performance of the Program of Genetic Counseling of Valencia Community. Mutational screening was performed by pre-screening the heteroduplex formed in the PCR products obtained amplifying BRCA1 and BRCA2 genes by conformation sensitive electrophoresis. We detected 10 deletereous mutations, four in BRCA1 (three frame-shift (FS) and one nonsense mutation (NS)) and six in BRCA2 (four FS and one NS mutation). Moreover, we detected 13 unclassified variants, four in BRCA1 (one missense (MS), two synonymous (SYN) and one intronic (I) variant) and nine in BRCA2 (six MS, one SYN and two I). The relevance of the novel mutations is discussed. Our contribution broadens the BRCA1/2 world mutational spectra.

[Molecular study of the BRCA1 and BRCA2 genes in 153 breast cancer families from Castilla and León (Spain): new nine unclassified variants identified]

BACKGROUND

It is estimated that 5-10% of breast cancers have an hereditary origin, germline mutations of BRCA1 and BRCA2 genes causing a predisposition. In the present study we analyzed BRCA1 and BRCA2 mutations in moderate to high risk breast cancer patients in order to find out the types and frequency of these mutations in the Spanish regional community of Castilla y León.

PATIENTS AND METHOD

We studied 207 moderate to high risk patients from 153 selected families. Genomic DNA was extracted from peripheral blood and analyzed by multiplex polymerase chain reaction-heteroduplexes-conformation sensitive gel electrophoresis (multiplex PCR-HA-CSGE). All variants detected were sequenced to further verify the mutation.

RESULTS

45 alterations (23 in BRCA1 and 22 in BRCA2) were identified in 74 families (48.4%), corresponding to 13 polymorphisms (29 families), 19 unclassified variants (26 families) of which 9 have not been previously described and 13 cancer-prone mutations (19 families; 12.42% of all families). Eight out of the 19 deleterious mutations (42.1%) were detected in the BRCA1 gene and 11 (57.9%) in the BRCA2 gene. The most prevalent mutation was 3036delACAA, which was detected in four unrelated families.

CONCLUSIONS

The high proportion of mutations, polymorphisms and unclassified variants we have detected may be the result of the sensitive procedure and the risk selection criteria used in this study. There is a high proportion of unclassified variants. Their role in the disease must be clarified through more studies, including their typing in control samples.