Abstract 5615: Functional analysis of variants of uncertain significance in the MSH6 mismatch repair gene

Abstract

Abstract Lynch syndrome (LS) is a hereditary condition that increases patients’ lifetime risk of cancer, primarily colorectal cancer. LS is caused by germline mutations in mismatch repair (MMR) genes, MLH1, MSH2, MSH6, and PMS2. Identification and classification of these mutations is important in LS diagnosis for guiding treatment plans and preventative care for patients’ and their families. However, the consequences of some variants in these genes are not immediately obvious, granting them classification as variants of uncertain significance (VUS). Laboratory functional analysis to determine whether these variants disrupt MMR function in human cells can provide important evidence for understanding the pathogenicity of VUS and reclassifying them. Half of known variants in the MMR gene MSH6 are VUS and, thus, the goal of my project is to provide evidence for a subset of these variants to help provide evidence for reclassification for these variants. We are calibrating and validating functional assays for MSH6 variants, using known MSH6 pathogenic and benign controls. We will then test MSH6 VUS identified in patients as reported in the InSiGHT database, ClinVar database, and current literature. We are using CRISPR gene editing to recreate these variants in the endogenous MSH6 loci in human embryonic stem cells (hESC). Using these edited hESC lines we are examining the impact of the variants on RNA and protein stability, repair of DNA microsatellites, which is a hallmark of normal MMR function, and induction of the MMR-dependent DNA damage response. With this compilation of data, we will convert the results into a quantitative Odds of Pathogenicity value. This Odds of Pathogenicity score can be used by expert variant interpretation committees to help readily reclassify these variants and provide a clearer diagnosis for these suspected Lynch syndrome patients. Citation Format: Elizabeth Szabo, Emily Blackburn, Alexander Radecki, Abhijit Rath, Christopher Heinen. Functional analysis of variants of uncertain significance in the MSH6 mismatch repair gene [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5615.