Genetic testing of Japanese patients with serrated polyposis syndrome: A multicentric study.

Abstract

75 Background: Serrated polyposis syndrome (SPS) is a rare condition associated with an increased risk of colorectal cancer. Previous studies have identified germline truncating variants of the RNF43; however, patients harboring these variants comprise a small part of those with SPS, in most of whom the causative gene remains unknown. To date, no study has described the genetic features of Japanese patients with SPS. The present study aimed to identify candidate causative genes of SPS in Japanese patients. Methods: Captures for equal to or more than 55 gene regions were performed using Agilent HaloPlex or Ion AmpliSeq technologies in SPS patients enrolled in The Study Group for Establishment of Diagnosis of Hereditary Gastrointestinal Tract Cancer Syndromes Based on a Next-Generation Sequencing Technology (SGHGCS). Whole exome sequencing of tumor tissue was performed whenever a candidate gene was identified. Results: Eleven patients (four males, seven females) were enrolled. Of these, nine had a history of colorectal cancer; four had a family history of colorectal cancer; and two had a family history of polyposis. Genetic testing identified two variants of VUS, POLD1 c.670C>T (p.R224C) and BRCA2 c.4169T>G (p.L1390W). Additionally, a nonsense variant, BUB1:c.1543G>T p.Gly515Ter was deemed likely to be pathogenic. The patient with the BUB1 variant was 47-year-old female with transverse colon cancer with more than 50 serrated polyps. She was a non-smoker. The variants detected in the transverse colon cancer did not include the canonical variants in common colorectal cancer, such as APC, KRAS or TP53 and were mostly transition substitutions (C>T). Conclusions: BUB1 was identified as a novel candidate causative gene of SPS in a patient with SPS with no smoking habit. These findings will hopefully contribute to our understanding of the genetic basis of SPS.