Search

The HH genotype of the nonconservative amino acid substitution polymorphism N372H in the BRCA2 gene was reported to be associated with a 1.3- to 1.5-fold increase in risk of both breast and ovarian cancer. As these studies concerned sporadic cancer cases, we investigated whether N372H and another common variant located in the 5'-untranslated region (203G > A) of the BRCA2 gene modify breast or ovarian cancer risk in BRCA1 mutation carriers. The study includes 778 women carrying a BRCA1 germ-line mutation belonging to 403 families. The two BRCA2 variants were analyzed by the TaqMan allelic discrimination technique. Genotypes were analyzed by disease-free survival analysis using a Cox proportional hazards model. We found no evidence of a significant modification of breast cancer penetrance in BRCA1 mutation carriers by either polymorphism. In respect of ovarian cancer risk, we also saw no effect with the N372H variant but we did observe a borderline association with the 5'-untranslated region 203A allele (hazard ratio, 1.43; CI, 1.01-2.00). In contrast to the result of Healey et al. on newborn females and adult female controls, we found no departure from Hardy-Weinberg equilibrium in the distribution of N372H alleles for our female BRCA1 carriers. We conclude that if these single-nucleotide polymorphisms do modify the risk of cancer in BRCA1 mutation carriers, their effects are not significantly larger than that of N372H previously observed in the general population.

Although screening for large deletions or duplications of the BRCA1 gene is becoming a routine component of the molecular diagnosis of familial breast cancer, little is known about the occurrence of such rearrangements in the BRCA2 gene. Because of the high frequency of BRCA2 mutations in breast cancer families with at least one case of male breast cancer, we selected a cohort of 39 such families, tested negative for mutations in the coding regions of BRCA1 and BRCA2, and developed an assay for BRCA2 rearrangements, based on quantitative multiplex PCR of short fluorescent fragments (QMPSF). We found three rearrangements: (1) a deletion of exons 12 and 13; (2) a duplication of exons 1 and 2; and (3) a complete deletion of BRCA2. We determined the boundaries of the deletion of exons 12 and 13, showing that it resulted from an unequal recombination between Alu sequences. We mapped the complete BRCA2 deletion, which extends over at least 298 kb and showed that it does not affect APRIN/AS3, previously characterized as a tumor suppressor gene, but it comprises several loci corresponding to proven or putative transcripts of unknown functional significance. These data suggest that screening for BRCA2 rearrangements should be done, especially in male breast cancer families tested negative for BRCA1 and BRCA2 mutations.

The glutathione S-transferase (GST) genes are involved in the metabolism of various carcinogens. Deletion polymorphisms in the genes GSTM1 and GSTT1 and a base transition polymorphism at codon 105 (Ile-->Val) in GSTP1 were investigated in relation to breast cancer risk. Tobacco smoking and reproductive factors were examined as potential effect modifiers. Individual data from seven case-control studies were pooled within the International Collaborative Study on Genetic Susceptibility to Environmental Carcinogens. To measure the effect of GSTs on breast cancer risk, odds ratios and 95% confidence intervals were computed adjusting for study center and age. The modifying effect was investigated by stratification on variables of smoking habits and reproductive history. A total of 2,048 cases with breast cancer and 1,969 controls were analyzed. The relative odds ratio (95% confidence interval) of breast cancer was 0.98 (0.86-1.12) with the GSTM1 null, 1.11 (0.87-1.41) with the GSTT1 null, 1.01 (0.79-1.28) with GSTP1 heterozygous mutants, and 0.93 (0.62-1.38) with GSTP1 homozygous mutants. Stratification by smoking or reproductive factors did not reveal a modifying effect of these variables, nor was there any association between GSTM1 and age at diagnosis of breast cancer. This is the largest study investigating susceptibility to breast cancer due to polymorphisms in the GST genes. The results conclusively show that single gene GST polymorphisms do not confer a substantial risk of breast cancer to its carriers. Furthermore, GSTs did not interact with smoking or reproductive history to modify cancer risk.

Strong inter- and intrafamilial variation of penetrance of breast and ovarian cancer is observed in BRCA1 mutation carriers. The wild-type copy of the BRCA1 gene is a plausible candidate as a cancer risk modifier given that the residual function corresponding to the intact BRCA1 allele may influence the process of tumor formation in BRCA1 carriers. Indeed, growing evidence is now becoming available on impaired reparation of double-strand DNA breaks in cells heterozygous for BRCA1 mutations, implying an enhanced mutability of BRCA1(+/-) cells. To determine whether certain variant forms of the wild-type BRCA1 allele are implicated in variation of the BRCA1-related cancer risk, their effect was studied in a panel of 591 women with BRCA1 germ-line mutations. We found that BRCA1 carriers with the wild-type BRCA1 copy bearing a common Gly1038 variant were at increased risk of ovarian cancer (hazards ratio, 1.50; 95% confidence interval, 1.03-2.19). The results of our study imply that a quite significant proportion of the interindividual variability in ovarian cancer penetrance in BRCA1 carriers may be explained by a common BRCA1 Gly1038 wild-type allele, given its high frequency (0.27).