Poster Presentation 47th Lorne Genome Conference 2026

TTN missense variant affecting a conserved Ig-domain residue as a cause of familial dilated cardiomyopathy (133798)

YuChen CC Chang 1 2 , Natalie Nowak 1 2 3 , Liny Tan 1 2 3 , Jodie Ingles 3 4 , Belinda Gray 1 2 3 , Charlotte Burns 1 2 3 , Richard Bagnall 1 2
  1. Faculty of Medicine and Health, The University of Sydney, Sydney, NSW, Australia
  2. Centenary Institute, Camperdown, NSW, Australia
  3. Department of Cardiology, Royal Prince Alfred Hospital, Sydney, NSW, Australia
  4. Genomics and Inherited Disease Program, Garvan Institute of Medical Research, Sydney, NSW, Australia

Background

Dilated cardiomyopathy (DCM) is a genetically heterogeneous disorder, with TTN truncating variants recognised as the most common monogenic cause. However, TTN missense variants remains a major interpretation challenge due to extensive background variation across the enormous titin protein. We identified a four-generation family with multiple individuals with DCM. By integrating phenotyping, exome/genome sequencing (ES/GS), and genome-wide linkage analysis (GWLA), we identified a TTN missense variant as the likely genetic cause for this family.

 

Methods

Echo- and electrocardiographic data were reviewed to classify cardiac phenotype across the pedigree. ES/GS was performed on selected affected individuals, followed by variant prioritisation and curation. GWLA was conducted using parametric MERLIN models under an autosomal-dominant inheritance model with incomplete penetrance.

 

Results

Eight family members met clinical criteria for DCM, including two individuals who progressed to end-stage heart failure requiring transplantation. Sequencing identified a pathogenic TTN truncating variant in one affected individual, but it did not segregate and was excluded as the familial cause.  A rare TTN missense variant located within an immunoglobulin-like (Ig) domain in a 100-PSI I-band exon segregated with all affected individuals. GWLA identifying a single linkage peak (LOD 1.9) at chr2q31 overlapping the TTN locus. The missense variant was absent from all versions of gnomAD and predicted deleterious by multiple in-silico tools. Structural alignment demonstrated evolutionary conservation of this amino acid across paralogous Ig-domains within titin, and two previously reported DCM-associated TTN missense variants affect the same residue at paralogous positions.

 

Conclusion

Through integrated phenotyping, ES/GS and GWLA, we identified a TTN missense variant as the most likely cause of DCM in this family. These findings highlight the utility of combining different genomic approaches to resolve variants of uncertain significance in large families. Structural and evolutionary analyses highlight a potential recurrent amino acid hotspot within titin I-band’s Ig-domains.