Detection of new alleles in genes predisposing to hereditary cancer

Doctoral Dissertation uoadl:2878817 101 Read counter

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Papamentzelopoulou Myrto-Sotiria
Dissertation committee:
Δημητρακάκης Κωνσταντίνος, Αναπληρωτής Καθηγητής, Ιατρικής Σχολής, ΕΚΠΑ
Λουτράδης Δημήτριος, Καθηγητής, Ιατρική,, ΕΚΠΑ
Γιαννουκάκος Δρακούλης, Διευθυντής Ερευνών, Εργαστήριο Μοριακής Διαγνωστικής, ΕΚΕΦΕ Δημόκριτος
Ροδολάκης Αλέξανδρος, Καθηγητής,Ιατρική, ΕΚΠΑ
Ζαγουρή Φλώρα, Αναπληρώτρια Καθηγήτρια, Ιατρική, ΕΚΠΑ
Θωμάκος Νικόλαος, Επίκουρος Καθηγητής, Ιατρική, ΕΚΠΑ
Κωνσταντοπούλου Ειρήνη, Ερευνήτρια Β’, Εργαστήριο Μοριακής Διαγνωστικής, ΕΚΕΦΕ Δημόκριτος
Original Title:
Ανίχνευση νέων αλληλομόρφων σε γονίδια που προδιαθέτουν για τον κληρονομικό καρκίνο
Translated title:
Detection of new alleles in genes predisposing to hereditary cancer
In the middle of the 1990’s it became clear that a substantial percentage (5-20%) of cancer diagnoses was due to genetic factors mainly characterized by an autosomal dominant inheritance pattern. These factors correspond to mutations in genes related to DNA repair mechanisms and result in loss of function of the corresponding proteins. Individuals carrying such mutations have a higher risk of developing cancer compared to general population and should be provided with personalized clinical surveillance whether they have been diagnosed with cancer or not. Through DNA sequencing of patients or healthy relatives it is feasible to identify such individuals in families with family history of cancer and/or younger ages at diagnosis.
Multigene panel testing provides a state of the art approach, through of which the identification of new genes, whose mutations predispose to hereditary breast and/or ovarian cancer, is feasible. It is estimated that about 5-10% of patients with breast cancer diagnosis carry pathogenic mutations in BRCA1 and BRCA2 genes and a maximum of 2.5% in ATM, CHEK2, PALB2, PTEN, TP53, etc. The corresponding percentages for epithelial ovarian cancer range between 20-30% for BRCA1 and BRCA2 and 6-15% for the rest of panel genes. A targeted clinical surveillance and additional preventive measures could be provided to such individuals, as well as genetic testing to 1st degree relatives. Accordingly, clinical actionability is highlighted through multigene panel use, especially when mutations are identified either in BRCA1/2 or ATM, CHEK2, PALB2 and TP53 genes, for which established clinical guidelines are provided (NCCN guidelines).
In the present thesis, an overall mutation prevalence of 12% for BRCA1/2 genes was estimated for a total of 50 patients selected based on NCCN guidelines for personal or family history of breast and/or ovarian cancer diagnosis. Specifically, half of the total identified mutations concerned Greek founder/recurrent mutations, in particular, the c.5382insC (c.5266dupC) mutation, a deletion of exon 20 (c.5256_5277+3179del3200) and a deletion of exons 23 and 24 (g.169527_180579del11052) of BRCA1.
A particular attention was given in the analysis of p.(Val1833Met) variant of BRCA1, due to the its high prevalence observed in both breast and ovarian cancer patients (1.82%) and ovarian cancer patients only (1.59%). The observation that p.(Val1833Met) variant co-segregates with the disease, the lack of co-existence with another pathogenic mutation and its absence in the control group discloses a cancer-related variant with pathogenic effect. In addition, through co-segregation analysis where the total likelihood ratio (LR) was calculated at 1.88, the p.(Val1833Met) variant is characterized as pathogenic. Haplotype analysis demonstrated the founder effect of p.(Val1833Met) variant, highlighting its Greek origin about 1,450 years ago. On the contrary, the prevalence of the recurrent in breast cancer cases p.Arg753Ter variant of PALB2 was extremely low in epithelial ovarian cancer patients, indicating that this variant is not an ovarian cancer-related one.
Finally, the implementation of massive parallel sequencing in patients with epithelial ovarian cancer diagnosis revealed an overall germline mutation prevalence of 29.1%. As expected, the majority of the pathogenic mutations is identified in BRCA1 and BRCA2 genes, with prevalences of 13.3% and 6.7%, respectively. Nevertheless, pathogenic mutations are identified in other genes, in particular, RAD51C (2.1%), FANC genes (FANCE, FANCL, FANCD2) (1.8%), as well as PPMID (1,4%), PALB2 (0.7%), CHEK2, NBN, PALB2, PMS1, PMS2, MLH1, DIS3L2, BLM, RECQL4 and ATM (0.35% each). In addition, an earlier age at diagnosis is observed in women carrying pathogenic mutations in BRCA1/2 compared to women that are either identified with mutations in non-BRCA1/2 genes or not carrying any pathogenic mutations. The present thesis also demonstrates that high-grade serous ovarian carcinomas are more related to BRCA1/2 mutations rather than non-BRCA1/2 mutations, whereas, endometrioid and clear-cell ovarian carcinomas are less related to BRCA1/2 mutations.
Main subject category:
Health Sciences
Hereditary cancer, Genes, Founder mutation
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