Genome-Wide Association Study-Driven Gene-Set Analyses, Genetic, and Functional Follow-Up Suggest GLIS1 as a Susceptibility Gene for Mitral Valve Prolapse

Background: Mitral valve prolapse (MVP) is a common heart valve disease, the most frequent indication for valve repair or replacement. MVP is characterized by excess extracellular matrix secretion and cellular disorganization, which leads to bulky valves that are unable to coapt correctly during ventricular systole resulting in mitral regurgitation, and it is associated with sudden cardiac death. Here we aim to characterize globally the biological mechanisms underlying genetic susceptibility to MVP to better characterize its triggering mechanisms. Methods: We applied i-GSEA4GWAS and DEPICT, two pathway enrichment tools to MVP genome-wide association studies. We followed-up the association with MVP in an independent dataset of cases and controls. This research was conducted using the UK Biobank Resource. Immunohistochemistry staining for Glis1 (GLIS family zinc finger 1) was conducted in developing heart of mice. Knockdown of Glis1 using morpholinos was performed in zebrafish animals 72 hours postfertilization. Results: We show that genes at risk loci are involved in biological functions relevant to actin filament organization, cytoskeleton biology, and cardiac development. The enrichment for positive regulation of transcription, cell proliferation, and migration motivated the follow-up of GLIS1, a transcription factor from the Krüppel-like zinc finger family. In combination with previously available data, we now report a genome-wide significant association with MVP (odds ratio, 1.20; P=4.36×10-10), indicating that Glis1 is expressed during embryonic development predominantly in nuclei of endothelial and interstitial cells of mitral valves in mouse. We also show that Glis1 knockdown causes atrioventricular regurgitation in developing hearts in zebrafish. Conclusions: Our findings define globally molecular and cellular mechanisms underlying common genetic susceptibility to MVP and implicate established and unprecedented mechanisms. Through the GLIS1 association and function, we point at regulatory functions during cardiac development as common mechanisms to mitral valve degeneration.