Mike Stratton

Genome-wide association study identifies five new breast cancer susceptibility loci

Breast cancer is the most common cancer in women in developed countries. To identify common breast cancer susceptibility alleles, we conducted a genome-wide association study in which 582,886 SNPs were genotyped in 3,659 cases with a family history of the disease and 4,897 controls. Promising associations were evaluated in a second stage, comprising 12,576 cases and 12,223 controls. We identified five new susceptibility loci, on chromosomes 9, 10 and 11 (P = 4.6 × 10−7 to P = 3.2 × 10−15). We also identified SNPs in the 6q25.1 (rs3757318, P = 2.9 × 10−6), 8q24 (rs1562430, P = 5.8 × 10−7) and LSP1 (rs909116, P = 7.3 × 10−7) regions that showed more significant association with risk than those reported previously. Previously identified breast cancer susceptibility loci were also found to show larger effect sizes in this study of familial breast cancer cases than in previous population-based studies, consistent with polygenic susceptibility to the disease.

Absence of methylation of CpG dinucleotides within the promoter of the breast cancer susceptibility gene BRCA2 in normal tissues and in breast and ovarian cancers.

Germline mutations of the BRCA2 gene on chromosome 13q12-q13 predispose to the development of early-onset breast cancer and ovarian cancer. Loss of heterozygosity detected using chromosome 13q markers in the vicinity of BRCA2 is observed in most cancers arising in carriers of germline BRCA2 mutations and also in 30-50% of sporadic breast and ovarian cancers. However, somatic mutations of BRCA2 are extremely rare in sporadic cancers. We have examined the hypothesis that expression of the BRCA2 gene may be suppressed in sporadic breast cancers by a mechanism that is associated with increased methylation of cytosine residues in the promoter region. Using a HpaII/MspI digestion-polymerase chain reaction based assay, the presence of 5-methylcytosine in three CpG dinucleotides within the BRCA2 promoter was assessed in 18 breast or ovarian cancer cell lines, in an SV40 large T antigen immortalized cell line derived from normal breast epithelial cells, in 64 primary sporadic breast cancers and peripheral blood leucocytes from these cases and in a number of other normal human tissues. Methylation was not detected in any of the tissues examined, suggesting that this mechanism of transcriptional repression is unlikely to explain the absence of somatic mutations in sporadic cancers.

Biallelic BRCA2 mutations are associated with multiple malignancies in childhood including familial Wilms tumour

Wilms tumour (WT) is an embryonal tumour of the kidney that occurs in 1 in 10 000 children. Familial clusters are rare and account for only 1–3% of cases. Mutations in WT1 account for a minority of WT families and two autosomal dominant familial WT predisposition genes have been mapped to chromosomes 17q21 and 19q13.1–3 However, a considerable proportion of familial WT pedigrees are not attributable to any of these loci.4nnFanconi anaemia (FA, MIM 227650) is a rare autosomal recessive condition affecting ∼1 in 300 000 children. FA is characterised by variable congenital abnormalities, short stature, bone marrow failure, hypersensitivity to DNA crosslinking agents, and a predisposition to haematological malignancies such as acute myeloid leukaemia in childhood.5 FA is heterogeneous and consists of at least 11 complementation groups, A, B, C, D1, D2, E, F, G, I, J, and L.6–8 Eight FA genes have been cloned and at least six FA proteins, FANCA, FANCC, FANCE, FANCF, FANCG, and FANCL, form a nuclear complex required for monoubiquitination of FANCD2. This modification promotes translocation of FANCD2 to DNA repair foci that also contain BRCA1, BRCA2, and RAD51.9nnIn 2002, Howlett and colleagues reported biallelic BRCA2 mutations in individuals with Fanconi anaemia D1 (FA-D1). Subsequently, additional FA-D1 and unclassified FA cases were examined and cases with BRCA2 mutations and WT and/or brain tumours were reported.10–13 These data prompted us to investigate BRCA2 in a familial WT pedigree, WILMS2, which includes siblings with both WT and brain tumours.4,14,15nn### Family reportnnWILMS2 was ascertained as part of our research on susceptibility to WT, which is approved by the London Multicentre Research Ethics Committee. The family includes two affected brothers with WT. The elder child first came to attention when his cryptorchidism was corrected at …

Heterozygosity for mutations in the ataxia telangiectasia gene is not a major cause of radiotherapy complications in breast cancer patients

Of patients being treated by radiotherapy for cancer, a small proportion develop marked long-term radiation damage. It is believed that this is due, at least in part, to intrinsic individual differences in radiosensitivity, but the underlying mechanism is unknown. Individuals affected by the recessive disease ataxia telangiectasia (AT) exhibit extreme sensitivity to ionizing radiation. Cells from such individuals are also radiosensitive in in vitro assays, and cells from AT heterozygotes are reported to show in vitro radiosensitivity at an intermediate level between homozygotes and control subjects. In order to examine the possibility that a defect in the ATM gene may account for a proportion of radiotherapy complications, 41 breast cancer patients developing marked changes in breast appearance after radiotherapy and 39 control subjects who showed no clinically detectable reaction after radiotherapy were screened for mutations in the ATM gene. One out of 41 cases showing adverse reactions was heterozygous for a mutation (insertion A at NT 898) that is predicted to generate a truncated protein of 251 amino acids. No truncating mutations were detected in the control subjects. On the basis of this result, the estimated percentage (95% confidence interval) of AT heterozygous patients in radiosensitive cases was 2.4% (0.1-12.9%) and in control subjects (0-9.0%). We conclude that ATM gene defects are not the major cause of radiotherapy complications in women with breast cancer.

Linkage and LOH studies in 19 cylindromatosis families show no evidence of genetic heterogeneity and refine the CYLD locus on chromosome 16q12–q13

Abstract. Familial cylindromatosis is an autosomal dominant predisposition to multiple neoplasms of the skin appendages. The susceptibility gene has previously been mapped to chromosome 16q12–q13 and has features of a recessive oncogene/tumour suppressor gene. We have now evaluated 19 families with this disease by a combination of genetic linkage analysis and loss of heterozygosity in cylindromas from affected individuals. All 15 informative families show linkage to this locus, providing no evidence for genetic heterogeneity. Recombinant mapping has placed the gene in an interval of approximately 1xa0Mb. There is no evidence, between families, of haplotype sharing that might be indicative of common founder mutations.

HPC2/ELAC2 polymorphisms and prostate cancer risk: analysis by age of onset of disease.

The candidate prostate cancer susceptibility gene HPC2/ELAC2 has two common coding polymorphisms: (Ser→Leu 217) and (Ala→Thr 541). The Thr541 variant in the HPC2/ELAC2 gene has previously been reported to be at an increased frequency in prostate cancer cases. To evaluate this hypothesis we genotyped 432 prostate cancer patients (including 262 patients diagnosed ⩽55 years) and 469 UK, population based control individuals with no family history of cancer. We found no significant difference in the frequencies of Thr541‐containing genotypes between cases and controls (OR=1.41, 95% CI 0.79–2.50). The association remained non-significant when the analysis was restricted to cases divided by age of onset into those diagnosed ⩽55 years (OR=1.50, 95% CI 0.79–2.85) or to patients diagnosed >55 years (OR=1.27, 95% CI 0.59–2.74). We conclude that any association between the Thr541 variant and prostate cancer is likely to be weak.

Evidence for susceptibility genes to familial Wilms tumour in addition to WT1, FWT1 and FWT2

Three loci have been implicated in familial Wilms tumour: WT1 located on chromosome 11p13, FWT1 on 17q12-q21, and FWT2 on 19q13. Two out of 19 Wilms tumour families evaluated showed strong evidence against linkage at all three loci. Both of these families contained at least three cases of Wilms tumour indicating that they were highly likely to be due to genetic susceptibility and therefore that one or more additional familial Wilms tumour susceptibility genes remain to be found.

Lobular carcinoma in situ of the breast is not caused by constitutional mutations in the E-cadherin gene

Lobular carcinoma in situ (LCIS) is an unusual histological pattern of non-invasive neoplastic disease of the breast occurring predominantly in women aged between 40 and 50 years. LCIS is frequently multicentric and bilateral, and there is evidence that it is associated with an elevated familial risk of breast cancer. Although women with LCIS suffer an increased risk of invasive breast disease, this risk is moderate suggesting that LCIS may result from mutation of a gene or genes conferring a high risk of LCIS, but a lower risk of invasive breast cancer. The high frequency of somatic mutations in E-cadherin in LCIS, coupled with recent reports that germline mutations in this gene can predispose to diffuse gastric cancer, raised the possibility that constitutional E-cadherin mutations may confer susceptibility to LCIS. In order to explore this possibility we have examined a series of 65 LCIS patients for germline E-cadherin mutations. Four polymorphisms were detected but no pathogenic mutations were identified. The results indicate that E-cadherin is unlikely to act as a susceptibility gene for LCIS.

Breast cancer susceptibility: a complex disease unravels

involved should eventually allow gene technology to be used more effec- tively to improve crop plants. Sense suppression has even proved advan- tageous when inactivation of specific genes is requiredz*. From a theor- etical standpoint, it is satisfying to witness the coalescence of plant re- search and work on related homology- dependent phenomena from diverse organisms. Together, these obser- vations should enrich our under- standing of both various epigenetic processes and the role of repetitive sequences in the regulation of eukaryotic gene expression. References 2 Ziman, J. (1994) Prometheus Bound: Science in a Dynamic Steady State, Cambridge University Press 2 Finnegan, J. and McElroy, D. (1994) Bioffechnology

Contribution of germline MLH1 and MSH2 mutations to lobular carcinoma in situ of the breast.

Lobular carcinoma in situ (LCIS) is an unusual histological pattern of non-invasive neoplastic disease of the breast occurring predominantly in women aged between 40 and 50 years. LCIS is frequently multicentric and bilateral suggesting a genetic basis to the disease. The high frequency of microsatellite instability in lobular breast cancers, coupled with increased risk of breast cancer associated with germline mismatch repair gene mutations raises the possibility that mutations MSH2 or MLH1 might confer susceptibility to LCIS. To explore this possibility we have examined a series of 71 LCIS patients for germline MSH2 and MLH1 mutations. No mutations were detected in MSH2. Two sequence variants were identified in MLH1. The first was a CTT-->CAT substitution, codon 607 (exon 16) changing leucine to histidine. The other mutation detected in MLH1 was a TAC-->TAA substitution codon 750 (exon 19) creating a stop codon, predicted to generate a truncated protein. These findings suggest that mutations in MLH1 may underlie a subset of LCIS cases.