Stop-Gain Mutations in PKP2 Are Associated with a Later Age of Onset of Arrhythmogenic Right Ventricular Cardiomyopathy

<div><p>Background</p><p>Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a cardiac disease characterized by the presence of fibrofatty replacement of the right ventricular myocardium, which may cause ventricular arrhythmias and sudden cardiac death. Pathogenic mutations in several genes encoding mainly desmosomal proteins have been reported. Our aim is to perform genotype-phenotype correlations to establish the diagnostic value of genetics and to assess the role of mutation type in age-related penetrance in ARVC.</p><p>Methods and Results</p><p>Thirty unrelated Spanish patients underwent a complete clinical evaluation. They all were screened for <i>PKP2, DSG2, DSC2, DSP, JUP</i> and <i>TMEM43</i> genes. A total of 70 relatives of four families were also studied. The 30 patients fulfilled definite disease diagnostic criteria. Genetic analysis revealed a pathogenic mutation in 19 patients (13 in <i>PKP2</i>, 3 in <i>DSG2</i>, 2 in <i>DSP</i>, and 1 in <i>DSC2)</i>. Nine of these mutations created a truncated protein due to the generation of a stop codon. Familial assessment revealed 28 genetic carriers among family members. Stop-gain mutations were associated to a later age of onset of ARVC, without differences in the severity of the pathology.</p><p>Conclusions</p><p>Familial genetic analysis helps to identify the cause responsible for the pathology. In discrepancy with previous studies, the presence of a truncating protein does not confer a worse severity. This information could suggest that truncating proteins may be compensated by the normal allele and that missense mutations may act as poison peptides.</p></div

ECG of family members.

<p>(A) Twelve-lead ECG of index case. The ECG shows QTc of 500 ms. (B) Twelve-lead ECG of mother’s index case. The ECG shows a normal QTc, and (C) a LQT during tachycardia registered by Holter. (D) Twelve-lead ECG of brother’s index case. The ECG shows QTc of 485 ms.</p

Pedigrees from 5 families.

<p>ARVC clinically affected individuals (grey round/square) and genetic carriers (black point inside round/square), not evaluated (question mark inside round/square), death (round/square with slash) and sudden death (grey round/square with slash). <b>A-</b> Family A. Index case is III.4 and carries c.2203 C>G (p.R735*) in <i>PKP2</i><b><i>.</i></b><b> B-</b> Family B. Index case is III.2 and carries c.2013delC (p.P671Pfs12*) in PKP2. <b>C-</b> Family C<b>.</b> Index case is II.4 and carries c.1912C>T (p.Q638*) in <i>PKP2</i>. <b>D-</b> Family D<b>.</b> Index case is II.1 and carries c.1237C> T (p.R413*). <b>E</b>- Family E. Index case is III.2, who carries a homozygous c.2440T>C (p.C814R) variation in the <i>DSG2</i> gene.</p

Representation of genetic results.

<p><b>A</b>- Prevalence of mutations in desmosomal genes. <b>B-</b> Prevalence of truncating protein mutations (black) and missense mutations (grey).</p

Pedigree and electropherogram.

<p>(A) Index case is II.1. White round/squares indicate healthy status after clinical evaluation. Grey round/squares indicate LQTS after clinical evaluation. Plus sign indicates carrier of genetic variation. Minus sign indicates non-carrier of the genetic variation. (B) Electropherogram of the genetic variation identified (p.R20729G_<i>TTN</i>).</p

Mutations identified in index cases.

<p>MAF = minor allele frequency consulted in European American (EA) individuals in exome sequencing project. N/I = variation not previously identified in general population. Genotype: HT = Heterozygous/HM = Homozygous. Predicted protein changed is named following Human genome variation society recommendations. ⁺Not available in public databases but already described as pathogenic mutation.</p

Representation of PKP2 domains.

<p><b>A-</b> Representation of wild type PKP2. It has HR2 domain and armadillo repeats domain (8 armadillo repeats, ARM). <b>B-</b> Representation of truncated PKP2 (PKP2^TR) and their domains. PKP2^TR p.92* and p.V202Vfs215* only have HR2 domain but not any of ARM repeats, p.R413* loses partially ARM 3 to C-terminus, and p.548fs562* loses partially ARM 4, p.Q638* conserve completely ARM 4 but loses the rest of protein until to C-terminus and p.R735* loses partially ARM6 to C-terminus. PKP2^TR p.K859V*881ent*48 extends their length to 930 amino acids.</p

List of the 55 SCD-related genes included in our panel and its association with the disease.

<p>List of the 55 SCD-related genes included in our panel and its association with the disease.</p

Clinical characteristics for Task Force Criteria (TFC) score.

<p>Clinical characteristics for Task Force Criteria (TFC) score.</p

NGS data showing CNV in the <i>KCNQ1</i> gene.

<p>(A) Coverage of all exons in the <i>KCNQ1</i> gene of several samples. (B) Detail coverage of exons 7 and 8 in several samples. (C) Normalized raw coverage of exons 7 and 8 showing a deletion in comparison to all other exons of the same gene. (D) In detail, normalized raw coverage of exons 7 and 8.</p