NFS-04. GENETIC COUNSELLING IN A MULTI-TUMOR PREDISPOSITION SYNDROME: A NOVEL FOUR-GENERATION TUNISIAN PEDIGREE

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Abstract BACKGROUND Cancer predisposition syndromes associated with an increased risk of CNS tumors and colorectal polyposis are heterogeneous inherited disorders associated with multiples genes. The delineation of the inheritance pattern and the management of the genetic testing are recommended for optimal care of patients and their families. Our aim was to report a cancer predisposition brain tumor-polyposis syndrome in a four-generation Tunisian consanguineous pedigree characterized by uncommon tumors localizations. METHODS The index case was a 43-year-old infertile woman presented to our genetic counselling because of a suspected familial cancer predisposition syndrome. She consulted for digestive symptoms with epigastralgia. Six adenomatous polyposis of the colon were confirmed histologically. Her sister died of colon cancer at the age of 50. She developed a malignant mesenteric recurrence after surgical resection of a moderately differentiated adenocarcinoma infiltrating the meso fat with lymph node metastases. Their three sisters and brother did not have any cancer. From the same third generation, only one cousin died of a brain cancer identified as a glioblastoma at the age of 43. Their maternal grandmother and her two brothers died of respectively breast, laryngeal and urothelial cancers. The second generation and fourth generation involved healthy members. RESULTS Analysis of the pedigree of this family indicated an autosomal recessive mode of inheritance of the brain tumor-polyposis syndrome. Clinically, there was uncommon association with breast, laryngeal and urothelial cancers in the first generation and brain/colon cancers in the third generation. CONCLUSIONS A recessive multi-tumor predisposition syndrome related to high microsatellite instability resulting in a mismatch repair deficiency seems to be the most reliable diagnosis in this family. Familial NTHL1 tumor and MUTYH associated polyposis syndromes were also suspected. NGS-based testing, from whole exome sequencing to multigene panel testing, is suggested as the most accurate genetic testing in such heterogeneous multi-tumor predisposition syndromes.