Low proportion of BRCA1 and BRCA2 mutations in Finnish breast cancer families: evidence for additional susceptibility genes

Identification of a founder BRCA2 mutation in Sardinia

Sardinian population can be instrumental in defining the molecular basis of cancer, using the identity-by-descent method. We selected seven Sardinian breast cancer families originating from the northern-central part of the island with multiple affected members in different generations. We genotyped 106 members of the seven families and 20 control nuclear families with markers flanking BRCA2 locus at 13q12-q13. The detection of a common haplotype shared by four out of seven families (60%) suggests the presence of a founder BRCA2 mutation. Direct sequencing of BRCA2 coding exons of patients carrying the shared haplotype, allowed the identification of a 'frame-shift' mutation at codon 2867 (8765delAG), causing a premature termination-codon. This mutation was found in breast cancer patients as well as one prostate and one bladder cancer patient with shared haplotype. We then investigated the frequency of 8765delAG in the Sardinian breast cancer population by analysing 270 paraffin-embedded normal tissue samples from breast cancer patients. Five patients (1.7%) were found to be positive for the 8765delAG mutation. Discovery of a founder mutation in Sardinia through the identity-by-descent method demonstrates that this approach can be applied successfully to find mutations either for breast cancer or for other types of tumours.

Genetic predisposition, environment and cancer incidence: a nationwide twin study in Finland, 1976-1995

Twin studies integrate genetic and environmental (including physical environment and life-style) information by comparing monozygotic and dizygotic twins for the occurrence of disease. Our objectives were to compare cancer incidence in twins with national rates and to estimate both the probability that co-twins of affected twins may develop cancer and the importance of genetic predisposition and environment in cancer development. The nationwide record linkage of the Finnish Twin Cohort Study, the Finnish Cancer Registry and the Central Population Register allowed the follow-up of 12,941 same-sexed twin pairs for incident primary cancers from 1976 to 1995. Zygosity was determined by use of a validated questionnaire in 1975. Methods included calculation of standardized incidence ratios and concordances and fitting of structural equation models. A total of 1,613 malignant neoplasms occurred in the cohort. The overall cancer incidence among twins resembled that among the general population. Monozygotic co-twins of affected twins were at 50% higher risk than were dizygotic co-twins. Based on genetic modeling, inherited genetic factors accounted for 18% (95% confidence interval 4-32%) of the liability in inter-individual variation in the risk of overall cancer, while non-genetic factors shared by twins accounted for 7% (0-16%) and unique environmental factors for 75% (65-85%). Our results appear to exclude a contribution greater than one-third for genetic predisposition in the development of cancer in the general population, thus pointing to the earlier confirmed substantial role of environment.

Germ-line TP53 mutations in Finnish cancer families exhibiting features of the Li-Fraumeni syndrome and negative for BRCA1 and BRCA2

Mutations in BRCA1 and BRCA2 account for a large portion of the inherited predisposition to breast and ovarian cancer. It was recently discovered that mutations in these two genes are less common in the Finnish population than expected. Because the genetic background of breast cancer, in particular, is largely obscure, it became necessary to search for mutations in other susceptibility genes. Because seven of our BRCA1 and BRCA2 mutation-negative families fulfilled the criteria of either Li-Fraumeni syndrome (LFS) or Li-Fraumeni-like syndrome (LFL), we decided to screen them for germ-line TP53 mutations in exons 5-8 using a dual-temperature single-strand conformation polymorphism assay (SSCP). Two missense mutations (Asn235Ser and Tyr220Cys) were identified. The clinical significance of these findings was evaluated by comparison to previously reported germ-line TP53 mutation data, and by using the tumor loss of heterozygosity (LOH) analysis. In addition, an immunohistochemical analysis of tumor specimens from mutation-positive individuals was performed. Our results suggest that the observed missense mutations confer susceptibility to cancer, and that germ-line TP53 mutations would therefore explain an additional fraction of hereditary breast cancer in Finland.

Frequency of BRCA1 mutation 5382insC in German breast cancer patients

OBJECTIVE

The aim of the study was to determine the frequency of the BRCA1 mutation 5382insC in German breast cancer patients with and without prior knowledge of a family history of breast cancer.

METHODS

Two groups of breast cancer patients were tested for the presence or absence of the 5382insC mutation using a PCR primer mismatch assay. A sample of 248 patients unrelated by genealogy was selected based on a history of breast and/or ovarian cancer in the families. In addition, a population-based sample of 800 unselected breast cancer patients was included in the analysis. Three intragenic DNA markers D17S1323, D17S1322, and D17S855, located at BRCA1 introns 12, 19, and 20, respectively, were utilized for allelic association studies as well as for haplotype analysis in 4 breast/ovarian cancer families.

RESULTS

The 5382insC mutation was identified in 10/248 (4.0%) familial breast cancer patients and in 8/800 (1.0%) unselected cases. Allelic association studies and haplotype analysis revealed an association of allele Nos. "6" at D17S1323 (chi2 value = 9.34, P = 0.007), "5" at D17S1322 (chi2 value = 3.62, P = 0.171), and "4" at D17S855 (chi2 value = 11.34, P = 0. 002) with the mutation 5382insC.

CONCLUSION

5382insC constitutes a frequent BRCA1 mutation in German breast cancer patients. The significant allelic association between this mutation and two intragenic DNA markers (D17S1323, D17S855) and the elevated allele frequency at marker D17S1322 suggest an ancient founder in the German breast cancer population. The PCR primer mismatch assay described herein provides a rapid and reliable detection method for the recurrent 5382insC mutation and will be useful for the analysis of large breast cancer populations.

Overestimation of hereditary breast cancer risk

OBJECTIVE

To find out how women with breast or ovarian cancer rate their chances of carrying hereditary factors for these cancers and to determine the extent to which they overestimate their risk.

SUMMARY BACKGROUND DATA

BRCA1 and BRCA2 are genes that cause breast and ovarian cancer when they are inherited in families. Testing for disease-associated mutations in these genes is now available commercially. Previous studies have shown that women overestimate their chances of carrying mutations. However, women's perceptions of risk have not been compared to objective estimates or to actual BRCA1 and BRCA2 testing results.

METHODS

This study examines estimates of carrying BRCA1 and BRCA2 mutations among women participating in a randomized trial comparing alternative precounseling educational materials. Estimates were provided by participants in a baseline mailed survey. Estimates given by participants were compared to those given by an expert panel and by a statistical model. Testing was offered free of charge and was done in an academic laboratory using standard techniques. Baseline estimates of participating women were compared to the estimates of the expert panel, to the carrier probability provided by the statistical model, and to actual testing results.

RESULTS

Women who have a personal history of breast or ovarian cancer significantly overestimate their risk of carrying hereditary factors for breast and ovarian cancer. Self-estimates exceeded the estimates of experts and a statistical model. One hundred women completed testing, and 21 mutations in BRCA1 or BRCA2 were found. Many test-negative women also overestimated their hereditary risk. Some women with a high carrier probability were negative for BRCA1 and BRCA2 mutations.

CONCLUSIONS

Overestimation of hereditary factors is common among affected women with a family history of cancer. Pretest education and counseling should reduce these high-risk perceptions. Better estimates of carrier probability will direct more intensive clinical services and research.