Greek BRCA1 and BRCA2 mutation spectrum: two BRCA1 mutations account for half the carriers found among high-risk breast/ovarian cancer patients

127 Greek breast/ovarian cancer families were screened for germline BRCA1/2 mutations by dHPLC followed by direct sequencing. Our results indicated 16 and 5 breast/ovarian cancer families bearing deleterious mutations in the BRCA1 and BRCA2 genes, respectively. Two novel BRCA2 germline mutations (G4X and 3783del10) are reported here for the first time. Subsequent compilation of our present findings with previously reported mutation data reveals that in a total of 287 Greek breast/ovarian cancer families, 46 and 13 carry a deleterious mutation in BRCA1 and BRCA2, respectively. It should be noted that two BRCA1 mutations, 5382insC and G1738R, both located in exon 20, account for 46% of the families found to carry a mutation. Based on our mutation analysis results, we propose here a hierarchical, cost-effective BRCA1/2 mutation screening protocol for individuals of Greek ethnic origin. The suggested protocol can impact on the clinical management of breast-ovarian cancer families on a national healthcare system level.

A rare RET gene exon 8 mutation is found in two Greek kindreds with familial medullary thyroid carcinoma: implications for screening

OBJECTIVE

Familial medullary thyroid carcinoma (FMTC) is caused by germ-line mutations in the RET proto-oncogene. These mutations concern mainly cysteine residues in exons 10 and 11, whereas noncysteine mutations in exons 13-16 are rare. Mutations in other exons have been reported only in isolated families. In this study we have analysed the RET gene in two FMTC families negative for mutations in the above exons.

DESIGN

We have analysed exons 7-19 and 21 in one index patient from each family using DNA sequencing.

PATIENTS

Twenty-eight subjects from both families were clinically assessed and subsequently molecularly analysed for the presence of RET gene mutations.

RESULTS

We have found the mutation c.1597G-->T (Gly533Cys) in two Greek families with FMTC. The mutation was detected in all seven MTC patients of both families as well as in 13 asymptomatic relatives in the heterozygote state, although one of the patients was also a homozygote due to consanguinity. The mutation shows a wide clinical heterogeneity, as there are carrier patients with age of diagnosis ranging from 23 to 88 years.

CONCLUSIONS

It is likely that this mutation causes FMTC, as no other mutation was found in the RET gene, the mutation co-segregates with FMTC, and family members without the mutation are clinically unaffected. As the same point mutation was previously found in a large Brazilian family, it may be present in other populations as well. Therefore, exon 8 of RET should be screened in FMTC families with no identified common RET mutations.

Thermal denaturation of the BRCT tandem repeat region of human tumour suppressor gene product BRCA1

Reduced stability of the tandem BRCT domains of human BReast CAncer 1 (BRCA1) due to missense mutations may be critical for loss of function in DNA repair and damage-induced checkpoint control. In the present thermal denaturation study of the BRCA1 BRCT region, high-precision differential scanning calorimetry (DSC) and circular dichroism (CD) spectroscopy provide evidence for the existence of a denatured state that is structurally very similar to the native. Consistency between theoretical structure-based estimates of the enthalpy (DeltaH) and heat capacity change (DeltaCp) and the calorimetric results is obtained when considering partial thermal unfolding contained in the region of the conserved hydrophobic pocket formed at the interface of the two BRCT repeats. The structural integrity of this region has been shown to be crucial for the interaction of BRCA1 with phosphorylated peptides. In addition, cancer-causing missense mutations located at the inter-BRCT-repeat interface have been linked to the destabilization of the tandem BRCT structure.

Germ line BRCA1 & BRCA2 mutations in Greek breast/ovarian cancer families: 5382insC is the most frequent mutation observed

BRCA1 and BRCA2 genes were screened for loss-of-function mutations in a series of 85 patients having at least one first- or second-degree relative affected by breast and/or ovarian cancer. All BRCA1 exons and BRCA2 exons 10 and 11 were screened with a combination of methods including SSCP, PTT and direct sequencing. We have found disease-associated mutations in 14 families (16.5%), eleven in BRCA1 and three in BRCA2. The known founder mutation 5382insC of BRCA1 was identified in seven unrelated families. The other mutations identified include the non-sense R1751X, the splice junction variant 5586G>A of BRCA1 and three frameshifts, 2024del5, 3034del4, and 6631del5, of BRCA2. Nine out of these 14 families had a family history of three or more breast/ovarian cancer cases. A large number of polymorphic or unclassified variants is also reported. Combined with our previously published data 5382insC was found in nine out of 20 families (45%), suggesting that this mutation may represent a common founder mutation in the Greek population.

BRCA2 gene mutations in Greek patients with familial breast cancer

Family history is a well-recognized risk factor for the development of breast cancer. The isolation of BRCA1 and BRCA2 genes, the two major predisposing genes in familial and to early onset breast and ovarian cancer, has resulted to the identification of a large number of families with mutations in these two genes. Despite the large number of distinct mutations detected in both genes, several mutations have been found to recur in unrelated families of diverse geographical origin. We have analyzed 27 Greek patients with familial breast cancer the majority of those having one first and one second degree relatives affected and 28 patients with sporadic breast cancer for BRCA2 germline mutations. The techniques used were single-strand conformation polymorphism analysis (SSCP) followed by sequencing. Furthermore, the clinical presentation and prognosis of BRCA2 associated breast cancer cases was compared to 20 adequately matched for age and date of diagnosis (within one year) sporadic breast cancer patients. We identified three novel BRCA2 mutations (3058delA, 6024delTA, and 4147delG) in the ovarian cancer cluster region (OCCR) and one already known (2024del5) germline BRCA2 gene mutation in five different breast cancer families. The 4147delG mutation was detected in two unrelated patients. BRCA2 germline mutations were correlated with early-onset breast cancer RR=4.77 (95% CI: 0.666-34.463). Although patients with BRCA2 germline mutations did not have a distinct histological phenotype they had an improved overall survival (100% vs 65%). Our findings suggest that there is a cluster of novel mutations in exons 10 and 11 in Greek patients with familial breast cancer. These mutations appear to have a milder clinical phenotype when compared to the rest of the study group.

Characterization of TCL, a new GTPase of the rho family related to TC10 andCcdc42

GTPases of the Rho family control a wide variety of cellular processes such as cell morphology, motility, proliferation, differentiation, and apoptosis. We report here the characterization of a new Rho member, which shares 85% and 78% amino acid similarity to TC10 and Cdc42, respectively. This GTPase, termed as TC10-like (TCL) is encoded by an unexpectedly large locus, made of five exons spanning over 85 kilobases on human chromosome 14. TCL mRNA is 2.5 kilobases long and is mainly expressed in heart. In vitro, TCL shows rapid GDP/GTP exchange and displays higher GTP dissociation and hydolysis rates than TC10. Using the yeast two-hybrid system and GST pull-down assays, we show that GTP-bound but not GDP-bound TCL protein directly interacts with Cdc42/Rac interacting binding domains, such as those found in PAK and WASP. Despite its overall similarity to TC10 and Cdc42, the constitutively active TCL mutant displays distinct morphogenic activity in REF-52 fibroblasts, producing large and dynamic F-actin-rich ruffles on the dorsal cell membrane. Interestingly, TCL morphogenic activity is blocked by dominant negative Rac1 and Cdc42 mutants, suggesting a cross-talk between these three Rho GTPases.

BRCA1 mutation analysis in breast/ovarian cancer families from Greece

Germline mutations in BRCA1 gene account for varying proportions of breast/ovarian cancer families, and demonstrate considerable variation in mutational spectra coincident with ethnic and geographical diversity. We have screened for mutations the entire coding sequence of BRCA1 in 30 breast/ovarian cancer women with family history of two or more cases of breast cancer under age 50 and/or ovarian cancer at any age. Genomic DNA from patient was initially analyzed for truncating mutations in exon 11 with PTT followed by DNA sequencing. In the cases where no frameshift mutation was observed in exon 11, all other exons were screened with direct sequencing. Two novel (3099delT, 3277insG) and three already described (3741insA, 1623del5-TTAAA, 5382insC-twice) truncating mutations were identified. In addition, 6 point mutations (L771L, P871L, E1038G, K1183R, S1436S, S1613G) which are already classified as polymorphisms were identified. Three unclassified intronic variants (IVS16-68 G>A, IVS16-92 G>A, IVS18+65G>A) were also detected. These results show that BRCA1 deleterious mutations are present in a fraction (20%) of Greek breast/ovarian cancer families similar to other European countries. Mutations were detected in high- (>/=3 members) as well as in moderate-risk (2 members) families. This is the first report of BRCA1 mutation analysis in Greece.