Characterization of two Ashkenazi Jewish founder mutations in MSH6 gene causing Lynch syndrome.

Founder mutations are an important cause of Lynch syndrome and facilitate genetic testing in specific ethnic populations. Two putative founder mutations in MSH6 were analyzed in 2685 colorectal cancer (CRC) cases, 337 endometrial cancer (EnCa) cases and 3310 healthy controls of Ashkenazi Jewish (AJ) descent from population-based and hospital-based case­control studies in Israel, Canada and the United States. The carriers were haplotyped and the age of the mutations was estimated. MSH6*c.3984_3987dupGTCA was found in 8/2685 CRC cases, 2/337 EnCa cases, and 1/3310 controls, consistent with a high risk of CRC (odds ratio (OR) = 9.9, 95% confidence interval (CI) = 1.2­78.9, p = 0.0079) and a very high risk of EnCa (OR = 19.6, 95% CI = 1.8­217.2, p = 0.0006). MSH6*c.3959_3962delCAAG was identified in 3/2685 CRC cases, 2/337 EnCa cases and no controls. Each mutation was observed on separate conserved haplotypes. MSH6*c.3984_3987dupGTCA and MSH6*c.3959_3962delCAAG probably arose around 585 CE and 685 CE, respectively. No carriers were identified in Sephardi Jews (450 cases and 490 controls). Truncating mutations MSH6*c.3984_3987dupGTCA and MSH6*c.3959_3962delCAAG cause Lynch syndrome and are founder mutations in Ashkenazi Jews. Together with other AJ founder mutations, they contribute substantially to the incidence of CRC and EnCa and are important tools for the early diagnosis and appropriate management of AJ Lynch syndrome patients.

Accuracy of BRCA1 and BRCA2 founder mutation analysis in formalin-fixed and paraffin-embedded (FFPE) tissue.

BACKGROUND: A major limitation in counseling unaffected women from families with inherited breast and ovarian cancer is that a "true-negative" interpretation of wild type BRCA analysis of the proband cannot be inferred in the absence of demonstration of a BRCA mutation segregating in the kindred. Documentation of familial BRCA mutations from paraffin-derived DNA of deceased patients has been limited due to reports of technical complications leading to lack of reproducibility of BRCA testing of archival material. METHODS: DNA was extracted from formalin-fixed paraffin-embedded (FFPE) morphologically normal tissue of 161 blinded, coded samples from women previously genotyped for the three Ashkenazi Jewish BRCA founder mutations from lymphocyte-derived DNA. Multiplex PCR followed by denaturing polyacrylamide gel electrophoresis was performed for the three founder mutations to determine if analysis on FFPE tissue could produce results concordant with those of the lymphocyte-derived DNA. RESULTS: After disclosure of the sample codes, the results were compared with the original lymphocyte-derived DNA genotypes. Excluding one sample unevaluable due to PCR failure, there was 100% concordance of 160 genotypes (120 mutation samples) derived from DNA from archival FFPE tissue compared to peripheral lymphocytes. CONCLUSIONS: The method described reliably detected BRCA founder mutations in archival DNA derived from FFPE tissue. These results suggests that this technique may be useful in clinical settings to inform wild type BRCA results of unaffected probands, leading to avoidance of unnecessary intensified surveillance or risk-reducing surgery. With further validation this approach can also be applied to other populations where founder mutations are observed.

Clinicopathologic features of BRCA-linked and sporadic ovarian cancer.

CONTEXT: Most hereditary ovarian cancers are associated with germline mutations in BRCA1 or BRCA2. Attempts to define the clinical significance of BRCA mutation status in ovarian cancer have produced conflicting results, especially regarding survival. OBJECTIVE: To determine whether hereditary ovarian cancers have distinct clinical and pathological features compared with sporadic (nonhereditary) ovarian cancers. DESIGN AND SETTING: Retrospective cohort study of a consecutive series of 933 ovarian cancers diagnosed and treated at our institution, which is a comprehensive cancer center as designated by the National Cancer Institute, over a 12-year period (December 1986 to August 1998). PATIENTS: The study was restricted to patients of Jewish origin because of the ease of BRCA1 and BRCA2 genotyping in this ethnic group. From the 189 patients who identified themselves as Jewish, 88 hereditary cases were identified with the presence of a germline founder mutation in BRCA1 or BRCA2. The remaining 101 cases from the same series not associated with a BRCA mutation and 2 additional groups (Gynecologic Oncology Group protocols 52 and 111) with ovarian cancer from clinical trials (for the survival analysis) were included for comparison. MAIN OUTCOME MEASURES: Age at diagnosis, surgical stage, histologic cell type and grade, and surgical outcome; and response to chemotherapy and survival for advanced-stage (II and IV) cases. RESULTS: Hereditary cancers were rarely diagnosed before age 40 years and were common after age 60 years, with mean age at diagnosis being significantly younger for BRCA1- vs BRCA2-linked patients (54 vs 62 years; P=.04). Histology, grade, stage, and success of cytoreductive surgery were similar for hereditary and sporadic cases. The hereditary group had a longer disease-free interval following primary chemotherapy in comparison with the nonhereditary group, with a median time to recurrence of 14 months and 7 months, respectively (P<.001). Those with hereditary cancers had improved survival compared with the nonhereditary group (P=.004). For stage III cancers, BRCA mutation status was an independent prognostic variable (P=.03). CONCLUSIONS: Although BRCA-associated hereditary ovarian cancers in this population have surgical and pathological characteristics similar to those of sporadic cancers, advanced-stage hereditary cancer patients survive longer than nonhereditary cancer patients. Age penetrance is greater for BRCA1-linked than for BRCA2-linked cancers in this population.

Molecular genetic characterization of BRCA1- and BRCA2-linked hereditary ovarian cancers.

Hereditary ovarian cancers associated with germline mutations in either BRCA1 or BRCA2 were studied to determine whether somatic mutation of the P53 gene is required for BRCA-linked ovarian tumorigenesis and further, whether the spectrum of additional somatic molecular genetic alterations present in these tumors differs from that known to exist in sporadic ovarian cancers. Forty tumors, 29 linked to BRCA1 and 11 linked to BRCA2, were examined for mutational alterations in P53, K-RAS, ERBB-2, C-MYC, and AKT2. The presence of a P53 mutation in 80% of these cancers indicates that P53 mutation is common but not required for BRCA-linked ovarian tumorigenesis; notably, a significantly higher proportion of the P53 mutations in BRCA2-linked cancers were deletions or insertions compared with the more typical spectrum of missense mutations seen in BRCA1-linked cancers. Additionally, BRCA-linked ovarian carcinomas seem to develop through a unique pathway of tumorigenesis that does not involve mutation of K-RAS or amplification of ERBB-2, C-MYC, or AKT2.

Mutation analysis of the putative tumor suppressor gene PTEN/MMAC1 in primary breast carcinomas.

A novel gene was identified recently at chromosome 10q23, named PTEN or MMAC1, and based on several criteria it was designated as a potential human tumor suppressor gene. Loss of heterozygosity affecting this region of 10q is observed in several cancer types, especially glioblastoma, and inactivating mutations of the PTEN/MMAC1 gene are found in some of these cancers as well as cell lines and xenografts. Breast cancer is among the tumor types in which mutations are documented, and germline mutations of the gene appear to be responsible for the rare autosomal dominant familial cancer syndrome known as Cowden disease, which includes breast cancer among its clinical features. To further determine the role that PTEN/MMAC1 mutations may play in breast tumorigenesis, the entire coding region was screened for mutations in 54 unselected primary breast cancers. Two mutations were identified, a somatic 2-bp deletion in an apparently sporadic breast cancer, and a germ-line 4-bp deletion in a breast cancer patient with a clinical history consistent with Cowden disease. These data indicate that somatic mutations of PTEN/ MMAC1 occur in only a small fraction of primary breast cancers and confirm the role of this gene in the etiology of Cowden disease. Evidence is also presented suggesting that numerous polymorphisms and missense variants exist in the PTEN/MMAC1 transcript.