Abstract 64: An Integrated Model for
Titin
Truncation Mutation Interpretation
Background: We recently discovered a conserved internal promoter in the Titin gene, which explains why truncating mutations in the C-terminal two thirds of the zebrafish ttna protein result in more severe disease, recapitulating a puzzling observation in human dilated cardiomyopathy (DCM) patients. Here we focus on the contribution of alternative splicing to the DCM phenotype, both in zebrafish Titin truncation mutants and in the context of an integrative model for Titin mutation interpretation. Methods and Results: Using CRISPR/Cas9, we disrupted an alternatively spliced exon in the I-band of Titin , normally present in zebrafish heart but absent in skeletal muscle. The resulting mutants had, on average, a milder cardiac phenotype than those with mutations in constitutive exons but also showed striking inter-sibling variability in disease expression, ranging from intact cardiac blood flow to severe early demise. The mutant exon demonstrated nonsense-altered splicing and disease severity paralleled selective deficiency in Titin transcript level, implying that variability in mutated exon inclusion coupled with nonsense-mediated decay (NMD) modulated phenotype. We next amassed Titin mutation information from 1785 human DCM cases and >68,000 controls to model mutation distribution and found three variance components 1) splicing; 2) internal isoform disruption; and 3) targeting of the C-terminal 2000 amino acids. An integrated model demonstrated strong predictive performance with an area under the receiver operating characteristic curve of 0.79 and correctly identified the highest risk individuals. Conclusions: We conclude that genetically targeted models and large-scale human data can be complementary in overcoming the challenges of genetic data interpretation.