Abstract 18977: Non-Syndromic Mitral Valve Prolapse From Gene Mutations to Modifiable Mechanisms

Abstract

Mitral valve prolapse (MVP) is a common disease affecting nearly 1 in 40 individuals. It is the leading surgical indication for mitral valve regurgitation. Despite a clear heritable component, the genetic etiology of non-syndromic MVP has remained elusive. Individuals from a large multigenerational family segregating non-syndromic MVP underwent capture sequencing of a previously linked interval on chromosome 11. We found a novel missense mutation in DCHS1, the human homologue of the Drosophila cell polarity gene dachsous (ds) that segregates with MVP in the family. The familial mutation reduced protein stability in zebrafish and cultured cells. Morpholino knockdown of zebrafish dachsous1b yielded a regurgitant atrioventricular canal defect that could be rescued by wild-type human DCHS1 but not by mRNA with the familial mutation. Adult haploinsufficient Dchs1 mice had anatomic and functional prolapse of thickened, elongated leaflets recapitulating the human MVP phenotype. Dchs1 haploinsufficiency was associated with developmental defects in valve shape, cell migration and patterning during fetal morphogenesis, suggesting cell polarity as a previously unrecognized facet of valve morphogenesis. Studies of downstream changes identified increased MAP kinase activities and α-SMA+ cells (myofibroblasts) in the valves preceding myxomatous degeneration; these suggest potential future directions for blunting disease progression. Additional genetic studies identified a second family with a DCHS1 mutation and a significantly increased burden of novel DCHS1 mutations in sporadic MVP cases Interdisciplinary studies strongly support DCHS1 as the first identified disease-causing gene for non-syndromic MVP and suggest potential mechanisms for modifying disease natural history.