Prevalence of Titin Truncating Variants in General Population

PLoS One. 2015 Dec 23;10(12):e0145284. doi: 10.1371/journal.pone.0145284. eCollection 2015.

Abstract

Background: Truncating titin (TTN) mutations, especially in A-band region, represent the most common cause of dilated cardiomyopathy (DCM). Clinical interpretation of these variants can be challenging, as these variants are also present in reference populations. We carried out systematic analyses of TTN truncating variants (TTNtv) in publicly available reference populations, including, for the first time, data from Exome Aggregation Consortium (ExAC). The goal was to establish more accurate estimate of prevalence of different TTNtv to allow better clinical interpretation of these findings.

Methods and results: Using data from 1000 Genomes Project, Exome Sequencing Project (ESP) and ExAC, we estimated the prevalence of TTNtv in the population. In the three population datasets, 52-54% of TTNtv were not affecting all TTN transcripts. The frequency of truncations affecting all transcripts in ExAC was 0.36% (0.32% - 0.41%, 95% CI) and 0.19% (0.16% - 0.23%, 95% CI) for those affecting the A-band. In the A-band region, the prevalences of frameshift, nonsense and essential splice site variants were 0.057%, 0.090%, and 0.047% respectively. Cga/Tga (arginine/nonsense-R/*) transitional change at CpG mutation hotspots was the most frequent type of TTN nonsense mutation accounting for 91.3% (21/23) of arginine residue nonsense mutation (R/*) at TTN A-band region. Non-essential splice-site variants had significantly lower proportion of private variants and higher proportion of low-frequency variants compared to essential splice-site variants (P = 0.01; P = 5.1 X 10-4, respectively).

Conclusion: A-band TTNtv are more rare in the general population than previously reported. Based on this analysis, one in 500 carries a truncation in TTN A-band suggesting the penetrance of these potentially harmful variants is still poorly understood, and some of these variants do not manifest as autosomal dominant DCM. This calls for caution when interpreting TTNtv in individuals and families with no history of DCM. Considering the size of TTN, expertise in DNA library preparation, high coverage NGS strategies, validated bioinformatics approach, accurate variant assessment strategy, and confirmatory sequencing are prerequisites for reliable evaluation of TTN in clinical settings, and ideally with the inclusion of mRNA and/or protein level assessment for a definite diagnosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cardiomyopathy, Dilated / genetics*
  • Connectin / chemistry
  • Connectin / genetics*
  • DNA Mutational Analysis
  • Databases, Genetic
  • Genetic Variation*
  • Humans
  • Polymorphism, Single Nucleotide
  • Prevalence
  • Sequence Analysis, DNA

Substances

  • Connectin
  • TTN protein, human

Grants and funding

This work was supported by grants from the Sigrid Jusélius Foundation; the Finnish Foundation for Pediatric Research; the Finnish Foundation for Cardiovascular Research; the Finnish Cultural Foundation (00150083:OA); and the Ida Montin Foundation (OA). The funders Blueprint Genetics had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The funder provided support in the form of salaries for authors [OA, JWK and TPA], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.