title: Prevalence of Titin Truncating Variants in General Population.
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.
  
  
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Children's Hospital Helsinki, Institute of Clinical Medicine, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Oyediran
authors.initials: O
authors.lastname: Akinrinade
authors.affiliation: Blueprint Genetics, Helsinki, Finland.|Department of Clinical Physiology and Nuclear Medicine, HUS Medical Imaging Center, Helsinki University Central Hospital and University of Helsinki, Finland.
authors.forename: Juha W
authors.initials: JW
authors.lastname: Koskenvuo
authors.affiliation: Children's Hospital Helsinki, Institute of Clinical Medicine, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland.|Blueprint Genetics, Helsinki, Finland.
authors.forename: Tero-Pekka
authors.initials: TP
authors.lastname: Alastalo
mesh_terms: D002311:Cardiomyopathy, Dilated / Q000235:genetics*; D064211:Connectin / Q000737:chemistry / Q000235:genetics*; D004252:DNA Mutational Analysis; D030541:Databases, Genetic; D014644:Genetic Variation; D006801:Humans; D020641:Polymorphism, Single Nucleotide; D015995:Prevalence; D017422:Sequence Analysis, DNA
chemical_list: D064211:Connectin; C577285:TTN protein, human