Qun Niu

Evaluation of 19 susceptibility loci of breast cancer in women of African ancestry

Multiple breast cancer susceptibility loci have been identified in genome-wide association studies (GWAS) in populations of European and Asian ancestry using array chips optimized for populations of European ancestry. It is important to examine whether these loci are associated with breast cancer risk in women of African ancestry. We evaluated 25 single nucleotide polymorphisms (SNPs) at 19 loci in a pooled case-control study of breast cancer, which included 1509 cases and 1383 controls. Cases and controls were enrolled in Nigeria, Barbados and the USA; all women were of African ancestry. We found significant associations for three SNPs, which were in the same direction and of similar magnitude as those reported in previous fine-mapping studies in women of African ancestry. The allelic odds ratios were 1.24 [95% confidence interval (CI): 1.04-1.47; P = 0.018] for the rs2981578-G allele (10q26/FGFR2), 1.34 (95% CI: 1.10-1.63; P = 0.0035) for the rs9397435-G allele (6q25) and 1.12 (95% CI: 1.00-1.25; P = 0.04) for the rs3104793-C allele (16q12). Although a significant association was observed for an additional index SNP (rs3817198), it was in the opposite direction to prior GWAS studies. In conclusion, this study highlights the complexity of applying current GWAS findings across racial/ethnic groups, as none of GWAS-identified index SNPs could be replicated in women of African ancestry. Further fine-mapping studies in women of African ancestry will be needed to reveal additional and causal variants for breast cancer.

Screening RAD51C nucleotide alterations in patients with a family history of breast and ovarian cancer.

It has been reported that one biallelic missense mutation in the RAD51C gene was found in a Fanconi anemia-like disorder and six monoallelic pathogenic mutations were identified in 480 BRCA1/2 negative breast and ovarian cancer pedigrees but not in 620 pedigrees with breast cancer only. Additionally, the RAD51C gene was reported to be involved in gene fusion events in the MCF-7 breast cancer cell line. We performed complete sequencing and fusion gene breakpoint screening to detect deleterious mutations and chromosomal structure change in the RAD51C gene. Ninety-two hereditary gynecological cancer patients with a family history of breast and ovarian cancer but not carrying BRCA1/2 mutations were studied. In addition, 46 breast cancer cell lines were screened for the gene fusion events. Ten DNA sequence variants but no deleterious mutations were identified. We did not observe the occurrence of the known gene fusion either. We were unable to confirm the contribution of the RAD51C gene to hereditary breast and ovarian cancer (HBOC) in this relatively small cohort. Nonetheless, larger studies in diverse populations to fully investigate the mutation spectrum of the RAD51C gene are needed.

High prevalence of BRCA1 and BRCA2 mutations in unselected Nigerian breast cancer patients

Inherited mutations in the BRCA1 and BRCA2 genes are the strongest genetic predictors of breast cancer and are the primary causes of familial breast/ovarian cancer syndrome. The frequency, spectrum and penetrance of mutant BRCA1/BRCA2 alleles have been determined for several populations, but little information is available for populations of African ancestry, who suffer a disproportionate burden of early onset breast cancer. We have performed complete sequence analysis of all BRCA1 and BRCA2 exons and intron–exon boundaries for 434 Nigerian breast cancer patients from the University College Hospital in Ibadan, Nigeria. In contrast to previous suggestions that BRCA1/BRCA2 mutation frequencies are low or undetectable in African American populations, we find that Nigerian breast cancer patients have an exceptionally high frequency of BRCA1 and BRCA2 mutations (7.1 and 3.9%, respectively). Sixteen different BRCA1 mutations were detected, seven of which have never been reported previously, while thirteen different BRCA2 mutations were seen, six of which were previously unreported. Thus, our data support enrichment for genetic risk factors in this relatively young cohort. To improve breast cancer outcomes, we suggest that family‐based models of risk assessment and genetic counseling coupled with interventions to reduce breast cancer risk should be broadly disseminated in Nigeria and other underserved and understudied populations.

Novel germline PALB2 truncating mutations in African American breast cancer patients.

It has been demonstrated that the partner and localizer of breast cancer 2 (PALB2) acts as a bridging molecule between the breast cancer 1 (BRCA1) and BRCA2 proteins and is responsible for facilitating BRCA2‐mediated DNA repair. Truncating mutations in the PALB2 gene reportedly are enriched in patients with Fanconi anemia and breast cancer in various populations.

UDP-glucuronosyltransferase 1A1 gene polymorphisms and total bilirubin levels in an ethnically diverse cohort of women

The objective of this study was to investigate variations in UGT1A1 polymorphisms and haplotypes among African-American and Caucasian women and to assess whether variants other than UGT1A1*28 are associated with total serum bilirubin levels. The (TA)n repeats and 14 single nucleotide polymorphisms (SNPs) in the UGT1A1 gene were genotyped in 335 African Americans and 181 Caucasians. Total serum bilirubin levels were available in a subset of 125 women. Allele frequencies of all SNPs and (TA)n repeats were significantly different between African Americans and Caucasians. In Caucasians, three common haplotypes accounted for 71.8% of chromosomes, whereas five common haplotypes accounted for only 46.6% of chromosomes in African Americans. Mean total serum bilirubin levels were significantly lower (p = 0.005) in African Americans (0.36 mg/dl) than in Caucasians (0.44 mg/dl). The (TA)n repeats explained a significant amount of variation in total bilirubin levels (R2 = 0.27, p < 0.0001), whereas other SNPs were less correlative. Thus, significant variations in UGT1A1 haplotype structure exist between African Americans and Caucasians in this relatively large cohort of women. The correlation of UGT1A1 with total bilirubin levels was mainly due to (TA)n repeats in Caucasians but a clear correlation was not observed in African Americans because of the high diversity of haplotypes and the small sample size. These data have implications for the design of epidemiologic studies of cancer susceptibility and pharmacogenetic studies for adverse drug reactions in populations of African ancestry.

Fine-mapping of Breast Cancer Genome-wide Association Studies Loci in Women of African Ancestry Identifies Novel Susceptibility Markers

Numerous single nucleotide polymorphisms (SNPs) associated with breast cancer susceptibility have been identified by genome-wide association studies (GWAS). However, these SNPs were primarily discovered and validated in women of European and Asian ancestry. Because linkage disequilibrium is ancestry-dependent and heterogeneous among racial/ethnic populations, we evaluated common genetic variants at 22 GWAS-identified breast cancer susceptibility loci in a pooled sample of 1502 breast cancer cases and 1378 controls of African ancestry. None of the 22 GWAS index SNPs could be validated, challenging the direct generalizability of breast cancer risk variants identified in Caucasians or Asians to other populations. Novel breast cancer risk variants for women of African ancestry were identified in regions including 5p12 (odds ratio [OR] = 1.40, 95% confidence interval [CI] = 1.11-1.76; P = 0.004), 5q11.2 (OR = 1.22, 95% CI = 1.09-1.36; P = 0.00053) and 10p15.1 (OR = 1.22, 95% CI = 1.08-1.38; P = 0.0015). We also found positive association signals in three regions (6q25.1, 10q26.13 and 16q12.1-q12.2) previously confirmed by fine mapping in women of African ancestry. In addition, polygenic model indicated that eight best markers in this study, compared with 22 GWAS-identified SNPs, could better predict breast cancer risk in women of African ancestry (per-allele OR = 1.21, 95% CI = 1.16-1.27; P = 9.7 × 10(-16)). Our results demonstrate that fine mapping is a powerful approach to better characterize the breast cancer risk alleles in diverse populations. Future studies and new GWAS in women of African ancestry hold promise to discover additional variants for breast cancer susceptibility with clinical implications throughout the African diaspora.

Microsatellites in the Estrogen Receptor (ESR1, ESR2) and Androgen Receptor (AR) Genes and Breast Cancer Risk in African American and Nigerian Women

Genetic variants in hormone receptor genes may be crucial predisposing factors for breast cancer, and microsatellites in the estrogen receptor (ESR1, ESR2) and androgen receptor (AR) genes have been suggested to play a role. We studied 258 African-American (AA) women with breast cancer and 259 hospital-based controls, as well as 349 Nigerian (NG) female breast cancer patients and 296 community controls. Three microsatellites, ESR1_TA, ESR2_CA and AR_CAG, in the ESR1, ESR2 and AR genes, respectively, were genotyped. Their repeat lengths were then analyzed as continuous and dichotomous variables. Analyses of continuous variables showed no association with breast cancer risk in either AA or NG at ESR1_TA; AA cases had shorter repeats in the long allele of ESR2_CA than AA controls (Mann-Whitney P  = 0.036; logistic regression P  = 0.04, OR  = 0.91, 95% CI 0.83–1.00), whereas NG patients had longer repeats in the short allele than NG controls (Mann-Whitney P  = 0.0018; logistic regression P  = 0.04, OR  = 1.06, 95% CI 1.00–1.11); and AA cases carried longer repeats in the short allele of AR_CAG than AA controls (Mann-Whitney P  = 0.038; logistic regression P  = 0.03, OR  = 1.08, 95% CI 1.01–1.15). When allele sizes were categorized as dichotomous variables, we discovered that women with two long alleles of ESR2_CA had increased risk of breast cancer (OR  = 1.38, 95% CI 1.10–1.74; P  = 0.006). This is the first study to investigate these three microsatellites in hormonal receptor genes in relation to breast cancer risk in an indigenous African population. After adjusting for multiple-testing, our findings suggest that ESR2_CA is associated with breast cancer risk in Nigerian women, whereas ESR1_TA and AR_CAG seem to have no association with the disease among African American or Nigerian women.

Lack of association between common single nucleotide polymorphisms in the TERT-CLPTM1L locus and breast cancer in women of African ancestry.

As one of the most common cancers worldwide, breast cancer places an extraordinary burden on the populations of African ancestry. Common SNPs in the TERT-CLPTM1L locus have been reported to be associated with several types of cancer, including breast cancer. We sought to investigate whether the previously reported common single nucleotide polymorphisms (SNPs) in the TERT-CLPTM1L locus could also contribute to the breast cancer risk in women of African ancestry. We genotyped eleven SNPs in 2,892 women of African descent but were unable to detect any significant association between TERT-CLPTM1L SNPs and their predispositions for breast cancer risk. Given the differences in linkage disequilibrium patterns across populations, our findings suggest that larger independent studies from diverse populations are expected to evaluate the importance of the TERT-CLPTM1L locus in breast cancer.

Genetic Susceptibility to Type 2 Diabetes and Breast Cancer Risk in Women of European and African Ancestry

Background: Epidemiologic studies have reported a positive association between type 2 diabetes (T2D) and breast cancer risk, independent of body weight. Methods: We investigated 40 genetic variants known to be associated with T2D in relation to breast cancer risk among 2,651 breast cancer cases and 2,520 controls of African or European ancestry that were pooled from seven studies. Results: We found that two T2D risk alleles in Caucasian women (rs5945326-G, rs12518099-C) and one in women of African ancestry (rs7578597-T) were positively associated with breast cancer risk at a nominal significance level of 0.05, whereas two T2D risk alleles were inversely associated with breast cancer risk in Caucasian women (rs1111875-C, rs10923931-T). The composite T2D susceptibility score (the number of risk allele) was not significantly associated with breast cancer risk. Conclusion: The association between established T2D genetic susceptibility variants and breast cancer risk in women of African or European ancestry is likely weak, if it does exist. Impact: The pleiotropic effects of known T2D risk alleles cannot explain the association between T2D and breast cancer risk. Cancer Epidemiol Biomarkers Prev; 21(3); 552–6. ©2012 AACR.

Inherited mutations in breast cancer genes in African American breast cancer patients revealed by targeted genomic capture and next-generation sequencing.

CRA1501 Background: African American (AA) women are disproportionately affected by early-onset and triple-negative breast cancer (TNBC). One explanation for these disparities may be a higher frequency of inherited mutations among AA women in genes in DNA repair pathways, including BRCA1 and BRCA2. Using targeted genomic capture and next generation sequencing (NGS), we screened DNA from AA women with breast cancer for mutations in all 18 known breast cancer genes. METHODS A total of 249 unrelated AA women with breast cancer were ascertained through the Cancer Risk Clinic at The University of Chicago. Genomic DNA was extracted from peripheral blood and 3 micrograms were used for targeted capture and sequencing. Average read depth across the 1.4 MB targeted region was 320-fold. Sequence reads were aligned and all classes of variants identified: point mutations, small insertions and deletions, and large genomic rearrangements. Only unambiguously damaging mutations were called: stops, complete genomic deletions, and missenses demonstrated experimentally to cause loss of protein function. Variants were validated by PCR or Taqman analysis. RESULTS Fifty-six of 249 subjects (22%) carried at least one loss-of-function mutation, distributed among BRCA1 (n=26), BRCA2 (n=20), CHEK2 (n=3), PALB2 (n=3), ATM (n=5), and PTEN (n=1). The majority of mutations were unique. Damaging mutations were carried by 30% of patients with TNBC, 27% of patients diagnosed at age ≤45, 49% with a second breast primary, and 30% with a family history of either breast or ovarian cancer in any close relative. CONCLUSIONS We present the first comprehensive screen of all known breast cancer susceptibility genes among AA women using NGS. Mutation carrier frequencies are >25% for major subsets of patients defined by tumor or host characteristics. These high carrier frequencies suggest the importance of screening for mutations in all breast cancer genes in all AA breast cancer patients diagnosed at a young age, with a family history, or with TNBC as a way to identify at-risk family members for life-saving interventions.