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 analysed. 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.