Genetic differences in familial adenomatous polyposis syndrome in a Hungarian population: A prospective single center study

BACKGROUND Familial adenomatous polyposis (FAP) is a disorder of autosomal dominant inheritance that is responsible for around 1% of colorectal cancer (CRC) cases. AIM To determine the mutation profile of FAP-specific to the Hungarian population. METHODS This prospective single-center study enrolled patients with clinically suspected FAP or attenuated FAP (aFAP). Whole-exome next-generation sequencing was performed to detect variants of 50 FAP priority genes and 173 CRC predisposing genes or other CRC disease-associated genes. To identify larger deletions and insertions, a multiplex amplifiable probe hybridization technique was used. The identified genes were then classified according to the American College of Medical Genetics and Genomics guidelines. RESULTS A total of 26 index patients with clinically suspected FAP (n = 21) and aFAP (n = 5) were enrolled. APC gene alterations were confirmed in 92.31% of the cases (region 1B deletion, n = 2; whole-gene deletion, n = 4; frameshift mutation, n = 2; nonsense mutation, n = 5, and splice mutation, n = 1), with the remaining two cases having CHEK2 and MSH3 gene alterations. According to pathogenicity, 21 cases had pathogenic mutations, 6 cases had likely pathogenic mutations, and 16 cases had variants of unknown significance (VUS). The most frequent of the latter were the POLE (n = 5) and PIEZO1 (n = 4) gene variants. CONCLUSION Germline mutations in the APC gene were confirmed in more than 90% of Hungarian patients with clinically suspected FAP. Although the role of VUS genes is unclear, they are highly likely to play a role in the development of CRC.