Mutations in the NBS1 gene have been identified as disease-causing mutations in patients with Nijmegen Breakage Syndrome (NBS), but their clinical impact on breast cancer susceptibility has remained uncertain. We determined the frequency of 2 NBS mutations, 657del5 and R215W, in two large series of breast cancer cases and controls from Northern Germany and from the Republic of Belarus. The 5-bp-deletion 657del5 was identified in 15/1,588 cases (0.9%) from Belarus and in 1/1,076 cases (0.1%) from Germany but in only 1/1,014 population controls from Belarus and 0/1017 German controls (p < 0.01). The missense substitution R215W was observed in 9/1,588 Byelorussian and 9/1,076 German patients (0.6% and 0.8%, respectively) but was also present in 5/1,014 Byelorussian and 2/1,017 German control individuals (adjusted OR 5 1.9, 95%CI 0.8-4.6, p 5 0.18). Studies of lymphoblastoid cell lines revealed that NBS1/p95 protein levels were reduced to 70% in cells from a heterozygous breast cancer patient carrying R215W and to 15% in cells from a NBS patient compound heterozygous for 657del5/R215W suggesting that the R215W substitution may be associated with protein instability. Levels of radiation-induced phosphorylation of Nbs1/p95(Ser343) were reduced to 60% and 35% of wildtype, respectively. Neither age at diagnosis nor family history of breast cancer differed significantly between carriers and noncarriers of NBS mutations. The combined data are in line with an about 3-fold increase in breast cancer risk for female NBS heterozygotes (OR 3.1; 95%CI 1.4-6.6) and indicate that the 657del5 deletion and perhaps the R215W substitution contribute to inherited breast cancer susceptibility in Central and Eastern Europe. ' 2007 Wiley-Liss, Inc.

The 1100delC mutation of the cell cycle checkpoint kinase 2 (CHEK2) gene confers an increased risk for breast cancer, but the clinical impact of other CHEK2 gene variants remains unclear. We determined the frequency of two functionally relevant CHEK2 gene mutations, I157T and IVS211G > A, in two large series of breast cancer cases and controls from two independent populations. Our first series consisted of a hospital-based cohort of 996 German breast cancer cases and 486 population controls, and the second series consisted of 424 breast cancer patients and 307 population controls from the Republic of Belarus. The missense substitution I157T was identified in 22⁄996 cases (2.2%) vs. 3⁄486 controls (0.6%; OR 5 3.6, 95% CI 1.1-12.2, p 5 0.044) in the German population and in 24⁄424 cases (5.7%) vs. 4⁄307 controls (1.3%; OR 5 4.5, 95% CI 1.6-13.2, p 5 0.005) in the Byelorussian cohorts. The splicing mutation IVS211G > A was infrequent in both populations, being observed in 3⁄996 German and 4⁄424 Byelorussian patients (0.3% and 0.9%, respectively) and in 1⁄486 German controls (0.2%; adjusted OR 5 4.0, 95% CI 0.5-30.8, p 5 0.273). Heterozygous CHEK2 mutation carriers tended to be diagnosed at an earlier age in both populations, but these differences did not reach statistical significance. Family history of breast cancer did not differ between carriers and noncarriers. Our data indicate that the I157T allele, and possibly the IVS211G > A allele, of the CHEK2 gene contribute to inherited breast cancer susceptibility. ' 2005 Wiley-Liss, Inc.Key words: breast cancer; CHEK2; Germany; Belarus Cell-cycle checkpoint kinase 2 (CHEK2) is a central mediator of cellular responses to DNA damage.1,2 Ionizing radiation activates the CHEK2 protein via ATM-mediated phosphorylation, 3,4 and activated CHEK2 kinase can phosphorylate several substrates, including Cdc25A, p53 and E2F1, which mediate cell cycle arrest and apoptosis.1,2,5 CHEK2 phosphorylation of the breast cancer susceptibility protein BRCA1 regulates DNA double-strand break repair, 6 and deletion of CHEK2 potentiates the incidence of mammary carcinomas in BRCA1 conditional mutant mice.7 A truncating variant of CHEK2, the 1100delC mutation, has been identified as a low-penetrance breast-cancer susceptibility allele. 8,9 Heterozygous 1100delC carriers have an approximately 2-fold increased risk for breast cancer.10 Furthermore, a potential association of the 1100delC mutation with colorectal and prostate cancers has been reported. 11-13The role of variants in CHEK2 other than 1100delC is less clear. Most studies have led to the conclusion that other CHEK2 mutations do not make a major contribution to breast cancer susceptibility.14-16 However, one more recent investigation suggests that the common I157T mutation may be associated with increased breast cancer risk. 17 Parallel work has provided evidence that the missense substitution I157T as well as the splicing mutation IVS211G>A may confer an elevated risk for prostate cancer. 13,18 To assess the role of these CHEK2 varia...

Two recent articles by Schmidt et al 1 and Weischer et al 2 provided compelling evidence that a truncating mutation in the CHEK2 gene, 1100delC, confers an about three-fold risk for breast cancer in the general Danish population and is associated with a worse breast cancer-specific survival in Dutch breast cancer patients. As addressed by Narod and Lynch 3 in the accompanying editorial, 1100delC is only one of the truncating mutations that exist in the CHEK2 gene. A larger CHEK2 deletion spanning the exons 9 and 10 has been described as a Czech founder mutation 4 and accounts for 0.9% of breast cancer patients in Poland, 5 while it has not yet been studied in other ethnic groups.We performed a breast cancer association study of two independent, hospital-based case-control series from Germany and from the Republic of Belarus, both of which had previously been tested for three other CHEK2 mutations (unpublished data). 6,7 We screened for the presence of the CHEK2dele(9,10) mutation using a previously established allele-specific duplex polymerase chain reaction assay, 5 and subsequently confirmed positive patients by long-range polymerase chain reaction. 4 In the first study from Belarus, the CHEK2dele(9,10) allele was identified in 13 of 1,440 Byelorussian breast cancer patients (0.9%) but in none of 881 female control individuals (Yates' corrected, P ϭ .01). Three of 13 Byelorussian patients reported a first-degree family history, and one patient had bilateral disease. In the second study from Germany, the deletion was detected in five of 990 German breast cancer patients (0.5%) and in one of 1,014 female control individuals (0.1%; odds ratio, 5.1; 95% CI, 0.6 to 44.1; P ϭ .2). Two of five German patients reported a first-degree family history of breast cancer, and one had metachronous bilateral disease. Altogether, the data indicate that the CHEK2dele(9,10) allele is associated with breast cancer (Mantel-Haenszel odds ratio, 15.2; 95% CI, 1.8 to 123.8; P ϭ .002) and constitutes a significant risk factor in Central and Eastern Europe.These findings confirm and expand the role of CHEK2 gene mutations in breast cancer susceptibility and suggest a need for studies addressing the clinical impact of CHEK2 mutations beyond 1100delC. A recent follow-up of CHEK2 mutation carriers at Hannover Medical School (Hannover, Germany) has provided sugges-tive evidence that the worse survival of CHEK2 heterozygous breast cancer patients may not be limited to carriers of the 1100delC mutation, 8 but could be a more general feature of germ-line mutations in the CHEK2 gene. Larger studies of other common mutations, such as CHEK2dele(9,10), may prove helpful to further elucidate this issue and to finally translate the combined observations into improved clinical care.

The NBS1/p95 protein has a pivotal role in the sensing and repair of chromosome breaks. A missense mutation in the NBS1 gene, I171V, has recently been associated with a ninefold increased risk of breast cancer in Polish patients. Positive associations have also been reported for leukaemia and larynx cancer suggesting that I171V could be a more general susceptibility factor for malignancies. We investigated the prevalence of this mutation in two large hospital-based case-control series from Germany and from the Republic of Belarus. The I171V substitution was detected in 20/1,636 Byelorussian breast cancer patients and in 18/1,014 Byelorussian controls (OR: 0.68; 95%CI: 0.36-1.30, P=0.3). The I171V substitution was furthermore detected in 10/1,048 German breast cancer patients and in 7/1,017 German controls (OR: 1.39; 95%CI: 0.53-3.67, P=0.7). There were no significant differences between I171V carriers and non-carriers among the cases with regard to age at diagnosis, family history or bilateral occurrence of disease. A meta-analysis of all hitherto available studies did not reveal a difference in the prevalence of I171V between breast cancer cases and controls (OR: 1.05; 95%CI: 0.64-1.74, P=0.9). We conclude that the I171V substitution is unlikely to constitute a strong risk factor for breast cancer in our study populations.

The compositions and frequencies of Y-chromosome haplogroups identified by genotyping 23 biallelic loci of its nonrecombining region (