Arrhythmogenic Right Ventricular Cardiomyopathy-Associated Desmosomal Variants Are Rarely De Novo: Segregation and Haplotype Analysis of a Multinational Cohort

Edited by

Kalliopi Pilichou PhD, Cristina Basso MD, PhD, Genetics and Pathology, Padua University, Italy

Background

ARVC is a genetically determined cardiomyopathy caused mainly by rare genetic variants in genes encoding for desmosomal proteins i.e. desmoplakin (DSP), plakophilin-2 (PKP2), desmoglein-2 (DSG2), desmocollin-2 (DSC2) and plakoglobin.

American College of Medical Genetics (ACMG) and Genomics/Association for Molecular Pathology guidelines for variant interpretation designate both de novo status and identification in multiple unrelated probands with the same phenotype, as criteria towards pathogenicity. De novo variants in ARVC have been rarely reported (Pilichou et al., 2014).          

This multicenter study investigated the frequency and characteristics of de novo mutations as well as the likelihood of nonunique variants to have a common founder effect in different populations.

Methods

A retrospective multinational study from 3 cardiogenetic centers in Maryland (John Hopkins University Registry- U.S.), Netherlands (Netherlands Heart Institute Registry-E.U.) and Germany (Munster University Registry-E.U.), was performed in 322 ARVC probands carrying 327 pathogenic/likely pathogenic (P/LP) desmosomal variants. Definite diagnosis of ARVC was based on consensus Task Force criteria (TFC) (Marcus et al 2010).

Variants were classified as nonunique when were found in more than one ARVC TFC proband.

Variants were classified as de novo when cascade screening demonstrated absence of inheritance from the ancestors.

Results

A total of 327 P/LP desmosomal variants were identified in 322 unrelated ARVC probands. Of them, 88,4% were found in PKP2 (n=289), 5,2% in DSG2 (n=17), 4,8% in DSP and 1,5% in DSC2 genes. Of note, 4% of ARVC probands (n=13) had 3 whole gene deletions (2 PKP2 and 1 DSP).

Nonunique variants were found in 75,5% (n=247) of the cohort, most of which were found in PKP2 (n=230). Twenty-six nonunique PKP2 variants were shared in these 230 AC probands.

Cascade genetic screening was performed in 209 (64,9%) probands with 212 desmosomal variants that allowed for determination of inheritance. Only 3 of the 212 variants were apparently de novo (1,4%), 2 whole gene deletions (PKP2, DSP) and a missense variant in DSG2 (c.137G>A; p.Arg46Gln).

Haplotype analyses were performed in 24 of the 26 nonunique PKP2 variants present in 183 ARVC families to determine whether these nonunique variants were shared haplotypes. In 62,5%, (15 of the 24 variants) a common haplotype was found every 2 or 3 families studied whereas in the rest the number of haplotypes was far smaller the number of families studied.

Discussion

On the basis of the data collected in this multicenter study, the authors conclude that ARVC is caused mostly by desmosomal P/LP inherited nonunique variants, originating from ancient founders.

Since this study enrolled mostly PKP2 probands (88.4%, 289 of the 327 P/LP desmosomal carriers) and most of these PKP2 probands shared the same genetic variants (230 of the 289 PKP2 probands), the authors potentially overestimate the founder effect contribution in ARVC pathogenesis. As such, the conclusion of this multicenter study should not be extended tout court to the entire ARVC populations with other desmosomal genes but should be limited to PKP2 mutation carriers.

Although not the primary goal of this study, 13 (4%) of the P/LP desmosomal variants were large deletions, highlighting the importance of using genetic tests capable of identifying such deletions and the need of systematic analyses in larger cohorts to establish their frequency and role in disease pathogenesis.

Indeed, given the high risk of sudden cardiac death in ARVC beginning at puberty (Basso et al 1996), it is surprising that PKP2 variants are maintained in the population reflecting probably a much lower population/ family disease penetrance. Growing evidence suggests that ARVC penetrance may require multiple hits to reach a threshold of gene expression, as such it would have been of great interest clinical information of the family carriers were included in the paper.

De novo variants (1,4%) in this study was an extremely rare event supporting the idea that the variant pathogenicity criterion proposed by ACMG and Genomics/Association for Molecular Pathology, might have limited utility in adjudication of desmosomal variants. On the other hand, the association between large deletions and de novo variants is hard to support due to the rarity of de novo variants in this cohort and in the literature.

The results of this study strengthens the hypothesis that ARVC disease expression might be the result of multiple genetic and environmental factors, emphasizes the importance of routine genetic testing for large deletions and the need of larger cohorts and cascade screening to establish genetic variant pathogenicity in the era of widespread availability of genetic testing