Abstract 15160: Functional Clustering of Non-Truncating Mutations in Myosin Binding Protein C That Cause Hypertrophic Cardiomyopathy

• Published in: Circulation (New York, N.Y.) Vol. 138; no. Suppl_1 Suppl 1; p. A15160
• Main Authors: Thompson, Andrea D, Glazer, Amelia, Hafeez, Neha, Rodriguez, Juliani, Yob, Jamie, Jacoby, Daniel L, Colan, Steven D, Michels, Michelle, Olivotto, Iacopo, Ashley, Euan A, Ho, Carolyn Y, Helms, Adam, Day, Sharlene M
• Format: Journal Article
• Language: English
• Published: by the American College of Cardiology Foundation and the American Heart Association, Inc 06.11.2018
• ISSN: 0009-7322; 1524-4539

Myosin-binding protein C (MYBPC3) is the most commonly mutated gene in hypertrophic cardiomyopathy (HCM). While it is established that truncating MYBPC3 mutations cause haploinsufficiency, mechanisms of non-truncating mutations have not been elucidated. We hypothesize that non-truncating mutations exhibit clustering and locus-dependent functional effects.Methods & ResultsHCM patients with MYBPC3 mutations (925; 337 female) from the Sarcomere Human Cardiomyopathy Registry (SHaRe) were analyzed. Patients with non-truncating mutations (116) were diagnosed at a younger age than those with truncating mutations (33 ± 1.5 vs 40 ± 0.6 y, P<0.001). There were 12 unique non-truncating mutations in SHaRe with strong evidence of pathogenicity, defined as allele frequency <4E-05 in the Exome Aggregation Consortium AND either segregation or enrichment in the HCM population. Only 4 additional published mutations met these stringent criteria. Twelve of 16 mutations cluster in domains C3, C6, and C10. Mutations in C3 and C6 are near surface exposed flexible linker regions, predicted not to drastically alter protein stability. Conversely, mutations in C10 are in non-solvent exposed beta-strand regions, and may lead to destabilization. To test this hypothesis, MYBPC3 non-truncating mutations in C3 (Arg495Gln, Arg502Trp, Phe503Leu), C6 (Trp792Arg, Arg810His) and C10 (Leu1238Pro, Gly1248_Cys1253dup) were introduced into neonatal rat cardiomyocytes by adenoviral transduction. C3 and C6 mutations localized normally to the sarcomere and had similar protein stability compared to wild typeWT t1/24.1 hrs (95% CI 3.1-6.3), C3 and C6 mutant t1/21.9-5.9 hrs (each p>0.05 vs WT). In contrast, C10 mutant proteins aberrantly localized to the cytosol and were highly unstablet1/20.33 (0.22-0.7) and 0.40 (0.30-0.61) hrs respectively (P<0.05 vs WT).ConclusionDistinct from truncating mutations, non-truncating MYBPC3 mutations exhibit locus-dependent effects that suggest gain-of-function for mutations in internal domains, vs loss-of-function for mutations in the C-terminal domain. These findings have important implications for understanding causal mechanisms by which MYBPC3 mutations lead to HCM and for future design of disease-modifying therapies.