Mutation analysis of RAD51D in non-BRCA1/2 ovarian and breast cancer families.

BACKGROUND: Recent data show that mutations in RAD51D have an aetiological role in ovarian carcinoma, yet mutations do not appear to be associated with an increased risk for breast cancer. We studied ovarian and breast cancer families having at least one woman affected by ovarian carcinoma, to assess the importance of RAD51D mutations in such families. METHODS: The coding region of the RAD51D gene was analysed in 175 BRCA1/2-negative families with family histories of both ovarian and breast cancer ascertained from two Canadian and two Belgian institutions. RESULTS: We identified one previously reported deleterious mutation, p.Arg186(*) (c.556C>T), and two novel variants; missense substitution p.Cys119Arg and an intronic variant c.83-26A>G. p.Arg186(*) segregated with the disease in the family and two ovarian carcinomas available for analysis showed loss of the wild-type allele, but the novel variants are likely neutral. CONCLUSION: RAD51D should be included in genetic screening of ovarian cancer families that do not have BRCA1/BRCA2 mutations. We show that mutations are more likely to be found in families with two or more ovarian cancers, or in probands with first-degree relatives with ovarian cancer, and we feel testing should be preferentially offered to affected women from such families.

Evaluation of RAD51C as cancer susceptibility gene in a large breast-ovarian cancer patient population referred for genetic testing.

Despite extensive analysis of the BRCA1 and BRCA2 genes, germline mutations are detected in <20% of families with a presumed genetic predisposition for breast and ovarian cancer. Recent literature reported RAD51C as a new breast cancer susceptibility gene. In this study, we report the analysis of 410 patients from 351 unrelated pedigrees. All were referred for genetic testing and we selected families with at least one reported case of ovarian cancer in which BRCA1&2 mutations were previously ruled out. We analyzed the coding exons, intron-exons boundaries, and UTRs of RAD51C. Our mutation analysis did not reveal any unequivocal deleterious mutation. In total 12 unique sequence variations were identified of which two were novel. Our study and others suggest a low prevalence of RAD51C mutations with an exception for some founder populations. This observation is in favor of the rare allele hypothesis in the debate over the nature of the genetic contribution to individual susceptibility to breast and ovarian cancer and further genome-wide studies in high risk families are warranted.

Duplication of the VHL and IRAK2 genes in a patient with mental retardation/multiple congenital anomalies, epilepsy and ectomorphic habitus.

Partial 3p duplications are very rare. Often they are reported in translocations involving other chromosomes, whereas deletions encompassing the VHL gene in 3p25.3 predispose to Van-Hippel Lindau syndrome. We report here a paternally-inherited microduplication of 3p25.3 detected by array comparative genomic hybridisation (aCGH) in a 17 year-old male patient presenting with mental retardation and multiple congenital anomalies (MR/MCA), epilepsy and ectomorphic habitus. He has no tumour and there is no history of familial cancer. We refined the duplication by Multiplex Ligation-dependent Probe Amplification (MLPA) to a 251 kb region encompassing the VHL and IRAK2 genes. The duplication is likely to be causal. Interestingly, duplication of IRAK2 can cause epilepsy. Disruption of the GHRL gene can explain the ectomorphic habitus. To our knowledge, this is the smallest 3p duplication encompassing the VHL region. Its prognosis is unknown and a long-term follow-up is essential for an early diagnosis of malignancy.

Predominance of beta-catenin mutations and beta-catenin dysregulation in sporadic aggressive fibromatosis (desmoid tumor).

Aggressive fibromatosis (also called desmoid tumor) occurs as a sporadic lesion or as part of Familial Adenomatous Polyposis, which is caused by germ line mutations in the Adenomatous polyposis Coli (APC) gene. APC is involved in the regulation of the cellular level of beta-catenin, which is a mediator in Wnt signaling. Mutational analysis of the beta-catenin and APC genes was performed in 42 sporadic aggressive fibromatoses. Nine tumors had mutations in APC, and 22 had a point mutation in beta-catenin at either codon 45 or codon 41 (producing a stabilized beta-catenin protein product). Immunohistochemistry showed an elevated beta-catenin protein level in all tumors, regardless of mutational status. Beta-catenin localized to the nucleus, and was not tyrosine phosphorylated in the six tumors in which this was tested. The demonstration of mutations in two mediators in the Wnt-APC-beta-catenin pathway implicates beta-catenin stabilization as the key factor in the pathogenesis of aggressive fibromatosis. This is the first demonstration of somatic beta-catenin mutations in a locally invasive, but non metastatic lesion composed of spindle cells, illustrating the importance of beta-catenin stabilization in a variety of cell types and neoplastic processes. Moreover, this tumor has one of the highest reported frequencies of beta-catenin mutations of any tumor type.

Analysis of Wnt/Beta catenin signalling in desmoid tumors.

Desmoid tumors are fibromatous lesions occurring both sporadically and in patients with familial adenomatous polyposis (FAP). Because of the association of these tumors with the hereditary colorectal cancer syndrome FAP we set out to define the molecular events driving desmoid tumorigenesis, hypothezising these might be identical to events driving colorectal tumorigenesis. We found that whereas FAP-associated desmoid tumors are caused by germline APC mutations followed by somatic inactivation of the wild-type APC allele, sporadic desmoids are usually characterized by oncogenic mutations in the b-catenin gene, both identical molecular alterations to those found in the vast majority of colorectal cancers. Next we set out to investigate the cellular pathways activated by these mutations, and identified activation of the Wnt signaling pathway in desmoid tumors. Wnt signaling modulates expression of developmental genes and cell fate via beta-catenin, and has been implicated in many cancer types. Currently we are investigating tissue-specific downstream effectors of the Wnt pathway that might be responsible for the behaviour of these invasive fibrous tumors. Our findings also point to a role for this pathway in the regulation of normal myofibroblast proliferation and suggest novel treatments in desmoid tumors and other fibrous proliferative disorders.

Novel germline mutations in the APC gene and their phenotypic spectrum in familial adenomatous polyposis kindreds.

Among 23 germline mutations identified in the APC screening of 45 familial adenomatous polyposis (FAP) patients, we have found 10 different novel frameshift mutations in 11 apparently unrelated patients. In two cases, an additional missense mutation was detected. One previously described as a causative germline mutation (S2621C), associated with a 1-bp insertion (4684insA) on the opposite allele, did not segregate with the FAP phenotype in the family and was therefore considered as being non-pathogenic. The other (Z1625H) was located 2 codons before a 1-bp deletion (4897delC). Both mutations were transmitted together from an FAP father to his affected son. The FAP phenotype of these 10 novel truncating mutations was clinically documented within their kindreds. Important variability was observed in the phenotype. Interestingly, we noted that a mutation (487insT) localized at the boundary of the 5' attenuated APC phenotype region in two unrelated families resulted in classical polyposis. A clear-cut genotype-phenotype correlation could be drawn in only two instances. In one family, a 4684insA mutation led to a mild polyposis associated with early inherited osteomas and, in the family bearing the double mutation (Z1625H + 4897delC), the phenotype was obviously a 3' attenuated type. Our data illustrate the wide genetic and phenotypic heterogeneity of this condition between and within the families, making the establishment of correlations complex and any prediction in this disease difficult, although targeting the mutation site may be helpful in some specific cases.