Abstract 4177: Genetic testing for hereditary colorectal cancer syndromes in Algerian patients: A multicenter study
Authors: Cherbal Farid , Boumehdi Asma-Lamia , Khider Feriel , Landelouci Karima , Zemam Abdelwahab , Sabri Sarah , Damache Adam.Walid , Oukkal Mohammed , Mahfouf Hassen , Zebboudj Ferhat , Maaoui Mustapha 
Published: April 2023

Abstract
Background To date, 5% to 6 % of all colorectal cancers (CRCs) are associated with germline pathogenic variants in cancer predisposition genes that confer inherited predisposition to CRC. The use of genetic testing to identify individuals at risk for hereditary CRC syndromes can help to prevent the development of cancer and in the clinical management of the colorectal patients in the areas of both prevention and treatment. We report here the experience of our research laboratory of genetic testing for hereditary polyposis syndromes and Lynch syndrome (LS), respectively, in 126 patients.
Methods Fifty four (54) severe familial adenomatous polyposis (FAP) patients and 72-suspected Lynch syndrome (LS) patients, respectively, were selected from 2851 consecutive colorectal patients at five public hospitals during 2012-2019. Family histories of cancer were obtained from interviews, pedigrees and medical records of patients. Index cases and relatives diagnosed with FAP syndrome or Lynch syndrome have been tested for germline variants in APC, MLH1, MSH2, MSH6 and PMS2 genes, respectively, using PCR-Sanger Sequencing or by NGS using a cancer panel of 30 hereditary cancer genes (Color Genomics).
Results We detected 13 germline pathogenic variants in APC gene in 17 unrelated families, one germline pathogenic variant in BMPRA1 gene in juvenile polyposis syndrome (JPS) patient; seven (7) germline pathogenic variants and 2 variants of uncertain clinical significance (VUS) in MMR genes. Interestingly, 4 novel germline pathogenic variants in APC gene and 3 novel germline pathogenic variants in MMR genes, respectively, have been detected in our study. The most occurring germline pathogenic variants in APC gene were c.3927_3931del and c.4728dup that were identified in four and two index cases in 6 unrelated FAP families, respectively. In Lynch syndrome patients, the rare germline pathogenic variant MLH1 c.1546C&gt;T has been found in 21 individuals from 9 LS families, 6 of them related, with two large kindreds. In addition, the recurrent germline pathogenic variant MSH2 c.942+3A&gt;T has been detected in five unrelated index cases with a strong family history of LS syndrome. Moreover, the rare germline VUS PMS2 c.989-107_989-106insA has been detected in 14 unrelated LS patients and could be reclassified as likely benign. Interestingly, our NGS analysis detected the novel BMPR1A pathogenic variant c.1474-1G&gt;C in young JPS patient that has been misdiagnosed as FAP. The in-silico analysis for this novel variant showed an alteration of the wild type acceptor site and an activation of a cryptic acceptor site, respectively, most probably affecting splicing.
Conclusions Our current study will contribute to the molecular genetics characterization of hereditary colorectal cancer syndromes in Algerian population that is relevant for clinical management in the areas of genetic testing, early diagnosis, treatment and prevention.
Citation Format: Farid Cherbal, Asma-Lamia Boumehdi, Feriel Khider, Karima Landelouci, Abdelwahab Zemam, Sarah Sabri, Adam.Walid Damache, Mohammed Oukkal, Hassen Mahfouf, Ferhat Zebboudj, Mustapha Maaoui. Genetic testing for hereditary colorectal cancer syndromes in Algerian patients: A multicenter study. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4177.