Characterization of LTBP2 mutation causing Mitral Valve Prolapse

Background: Mitral Valve Prolapse (MVP) is a prevalent valvular disorder linked to considerable morbidity and mortality, affecting approximately 2.4% of the general population. A prior genome association study linked LTBP2 to this trait. We report a knockout mouse with LTBP2 mutation demonstrating valve phenotype as well as a family with a novel mutation causing MVP Methods: Exome sequencing and segregation analysis were conducted on a large pedigree to identify mutations associated with MVP. Using CRISPR-Cas9 technology, two strains of mice were generated: one with a complete knockout (KO) of the LTBP2 gene and another with a knock-in (KI) mutation corresponding to the putative causative mutation. Echocardiography and histological examinations of valves were performed in the KO and the KI at the age of 6 months. Optical coherence tomography (OCT) and histological examination of the eyes was done at the same time. mRNA qPCR analysis for TGFβ signaling targets (periostin/POSTN, RUNX2, and CTGF) in valve tissues was analyzed. Results: The LTBP2 rs117800773 V1506M mutation exhibited segregation with the MVP trait. LTBP2 KO mice had higher incidence of myxomatous changes by histology (7 of 9 of KO vs. 0 of 7 control animals, p=0.00186) and echocardiography (7 of 9 vs. 0 of 8, p=0.0011). LTBP2 Knock-in mice for the human mutation showed a significantly elevated myxomatous histological phenotype (8 of 8 vs. 0 of 9, p=0.00004) as well as by echocardiography (6 of 8 vs. 0 of 9, p=0.00123). KO mice demonstrated a significant increase in the depth of the anterior chamber as well as reduced visual acuity. LTBP2 KO mice demonstrated overexpression of both TGFβ signaling targets RUNX2 and periostin (P=0.0144 and P=0.001826, respectively). Conclusion: Animal models of LTBP2 KO and KI recapitulate MVP phenotype indicating that LTBP2 mutations are indeed causing myxomatous degeneration. Further, LTBP2 rs117800773 V1506M segregated with MVP in a large pedigree. Our data indicate the importance of LTBP2 in normal mitral valve function and that mutations in the gene care causing myxomatous valve.