Arrhythmogenic right ventricular cardiomyopathy type 6 (ARVC6): support for the locus assignment, narrowing of the critical region and mutation screening of three candidate genes

Genetics of inherited cardiomyopathies in Africa

In sub-Saharan Africa (SSA), the burden of noncommunicable diseases (NCDs) is rising disproportionately in comparison to the rest of the world, affecting urban, semi-urban and rural dwellers alike. NCDs are predicted to surpass infections like human immunodeficiency virus, tuberculosis and malaria as the leading cause of mortality in SSA over the next decade. Heart failure (HF) is the dominant form of cardiovascular disease (CVD), and a leading cause of NCD in SSA. The main causes of HF in SSA are hypertension, cardiomyopathies, rheumatic heart disease, pericardial disease, and to a lesser extent, coronary heart disease. Of these, the cardiomyopathies deserve greater attention because of the relatively poor understanding of mechanisms of disease, poor outcomes and the disproportionate impact they have on young, economically active individuals. Morphofunctionally, cardiomyopathies are classified as dilated, hypertrophic, restrictive and arrhythmogenic; regardless of classification, at least half of these are inherited forms of CVD. In this review, we summarise all studies that have investigated the incidence of cardiomyopathy across Africa, with a focus on the inherited cardiomyopathies. We also review data on the molecular genetic underpinnings of cardiomyopathy in Africa, where there is a striking lack of studies reporting on the genetics of cardiomyopathy. We highlight the impact that genetic testing, through candidate gene screening, association studies and next generation sequencing technologies such as whole exome sequencing and targeted resequencing has had on the understanding of cardiomyopathy in Africa. Finally, we emphasise the need for future studies to fill large gaps in our knowledge in relation to the genetics of inherited cardiomyopathies in Africa.

A New Algorithm for Counting Independent Motifs in Probabilistic Networks

Biological networks provide great potential to understand how cells function. Motifs are topological patterns which are repeated frequently in a specific network. Network motifs are key structures through which biological networks operate. However, counting independent (i.e., non-overlapping) instances of a specific motif remains to be a computationally hard problem. Motif counting problem becomes computationally even harder for biological networks as biological interactions are uncertain events. The main challenge behind this problem is that different embeddings of a given motif in a network can share edges. Such edges can create complex computational dependencies between different instances of the given motif when considering uncertainty of those edges. In this paper, we develop a novel algorithm for counting independent instances of a specific motif topology in probabilistic biological networks. We present a novel mathematical model to capture the dependency between each embedding and all the other embeddings, which it overlaps with. We prove the correctness of this model. We evaluate our model on real and synthetic networks with different probability, and topology models as well as reasonable range of network sizes. Our results demonstrate that our method counts non-overlapping embeddings in practical time for a broad range of networks.

Identification of Cadherin 2 ( CDH2 ) Mutations in Arrhythmogenic Right Ventricular Cardiomyopathy

Background—

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetically heterogeneous condition caused by mutations in genes encoding desmosomal proteins in up to 60% of cases. The 40% of genotype-negative cases point to the need of identifying novel genetic substrates by studying genotype-negative ARVC families.

Methods and Results—

Whole exome sequencing was performed on 2 cousins with ARVC. Validation of 13 heterozygous variants that survived internal quality and frequency filters was performed by Sanger sequencing. These variants were also genotyped in all family members to establish genotype–phenotype cosegregation. High-resolution melting analysis followed by Sanger sequencing was used to screen for mutations in cadherin 2 ( CDH2 ) gene in unrelated genotype-negative patients with ARVC. In a 3-generation family, we identified by whole exome sequencing a novel mutation in CDH2 (c.686A>C, p.Gln229Pro) that cosegregated with ARVC in affected family members. The CDH2 c.686A>C variant was not present in >200 000 chromosomes available through public databases, which changes a conserved amino acid of cadherin 2 protein and is supported as the causal mutation by parametric linkage analysis. We subsequently screened 73 genotype-negative ARVC probands tested previously for mutations in known ARVC genes and found an additional likely pathogenic variant in CDH2 (c.1219G>A, p.Asp407Asn). CDH2 encodes cadherin 2 (also known as N-cadherin), a protein that plays a vital role in cell adhesion, making it a biologically plausible candidate gene in ARVC pathogenesis.

Conclusions—

These data implicate CDH2 mutations as novel genetic causes of ARVC and contribute to a more complete identification of disease genes involved in cardiomyopathy.

Genomic Insights into Cardiomyopathies: A Comparative Cross-Species Review

In the global human population, the leading cause of non-communicable death is cardiovascular disease. It is predicted that by 2030, deaths attributable to cardiovascular disease will have risen to over 20 million per year. This review compares the cardiomyopathies in both human and non-human animals and identifies the genetic associations for each disorder in each species/taxonomic group. Despite differences between species, advances in human medicine can be gained by utilising animal models of cardiac disease; likewise, gains can be made in animal medicine from human genomic insights. Advances could include undertaking regular clinical checks in individuals susceptible to cardiomyopathy, genetic testing prior to breeding, and careful administration of breeding programmes (in non-human animals), further development of treatment regimes, and drugs and diagnostic techniques.

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D)

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a progressive genetic cardiomyopathy characterized by progressive fatty and fibrous replacement of ventricular myocardium. The clinical presentation is marked by ventricular arrhythmias, some fatal. The disease has evolved from a primary electrical/electrophysiological disorder (in the 1980s-1990s) to a diagnostic imaging conundrum (in the 2000s) to the current day understanding of a genetic cardiomyopathy caused by defects in cell-cell adhesion proteins or intracellular signaling components. The pathogenesis, clinical presentation, and the genetics of the disease are discussed in this review.

Recent advances in the epidemiology, pathogenesis and prognosis of acute heart failure and cardiomyopathy in Africa

This review addresses recent advances in the epidemiology, pathogenesis and prognosis of acute heart failure and cardiomyopathy based on research conducted in Africa. We searched Medline/PubMed for publications on acute decompensated heart failure and cardiomyopathy in Africa for the past 5 years (ie, 1 January 2008 to 31 December 2012). This was supplemented with personal communications with colleagues from Africa working in the field. A large prospective registry has shown that acute decompensated heart failure is caused by hypertension, cardiomyopathy and rheumatic heart disease in 90% of cases, a pattern that is in contrast with the dominance of coronary artery disease in North America and Europe. Furthermore, acute heart failure is a disease of the young with a mean age of 52 years, occurs equally in men and women, and is associated with high mortality at 6 months (∼18%), which is, however, similar to that observed in non-African heart failure registries, suggesting that heart failure has a dire prognosis globally, regardless of aetiology. The molecular genetics of dilated cardiomyopathy, hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy in Africans is consistent with observations elsewhere in the world; the unique founder effects in the Afrikaner provide an opportunity for the study of genotype-phenotype correlations in large numbers of individuals with cardiomyopathy due to the same mutation. Advances in the understanding of the molecular mechanisms of peripartum cardiomyopathy have led to promising clinical trials of bromocriptine in the treatment of peripartum heart failure. The key challenges of management of heart failure are the urgent need to increase the use of proven treatments by physicians, and the control of hypertension in primary care and at the population level.

Genome-wide association study of blood pressure response to methylphenidate treatment of attention-deficit/hyperactivity disorder

OBJECTIVE

We conducted a genome-wide association study of blood pressure in an open-label study of the methylphenidate transdermal system (MTS) for the treatment of attention-deficit/hyperactivity disorder (ADHD).

METHOD

Genotyping was conducted with the Affymetrix Genome-Wide Human SNP Array 6.0. Multivariate association analyses were conducted using the software package PLINK. After data cleaning and quality control we tested 316,934 SNPs in 140 children with ADHD.

RESULTS

We observed no genome-wide statistically significant findings, but a SNP in a K(+)-dependent Na(+)/Ca(2+) exchanger expressed in vascular smooth muscle (SLC24A3) was included in our top associations at p<1E-04. Genetic enrichment analyses of genes with ≥1 SNP significant at p<0.01, implicated several functional categories (FERM domain, p=5.0E-07; immunoglobulin domain, p=8.1E-06; the transmembrane region, p=4.4E-05; channel activity, p=2.0E-04; and type-III fibronectins, p=2.7E-05) harboring genes previously associated with related cardiovascular phenotypes.

CONCLUSIONS

The hypothesis generating results from this study suggests that polymorphisms in several genes consistently associated with cardiovascular diseases may impact changes in blood pressure observed with methylphenidate pharmacotherapy in children with ADHD.

Arrhythmogenic right ventricular cardiomyopathy as a cause of unexpected cardiac death in two horses

Postmortem and histological examination of the hearts from two horses, a five-year-old Clydesdale gelding and a 15-year-old cob gelding, revealed changes characteristic of arrhythmogenic right ventricular cardiomyopathy. In both cases, on gross examination, the right ventricular endocardium and interventricular septum were almost entirely replaced with a gelatinous yellow fibroareolar tissue. This tissue was histologically a combination of fibrous and adipose tissue that had replaced the normal myofibres and disrupted the Purkinje fibres.

Clinical features, survival experience, and profile of plakophylin-2 gene mutations in participants of the arrhythmogenic right ventricular cardiomyopathy registry of South Africa

Little is known about arrhythmogenic right ventricular cardiomyopathy (ARVC) in Africa. The objective of this study was to delineate the clinical characteristics, survival, and genetics of ARVC in South Africa. Information on clinical presentation, electrocardiographic and cardiac imaging findings, histology, and outcome of cases with suspected ARVC was collected using the standardised form of the ARVC Registry of South Africa. Genomic DNA was screened for mutations in plakophylin-2 (PKP2) gene. Survival and its predictors were analyzed using the Kaplan-Meier and Cox proportional hazards regression methods, respectively. Fifty unrelated cases who met the diagnostic criteria for ARVC were enrolled between January 2004 and April 2009. Clinical presentation was similar to that reported in other studies. Annual mortality rate was 2.82%, five-year cumulative mortality rate 10%, and mean age at death 36.9 +/- 14.7 years. Overall survival was similar to the general South African population (P = 0.25). Independent risk factors for death were syncope (Hazard Ratio [HR] 10.73, 95% Confidence Interval [CI] 1.88-61.18, P = 0.008) and sustained ventricular tachycardia (HR = 22.97, 95%CI 2.33-226.18, P = 0.007). Seven PKP2 gene mutations were found in 9/36 (25%) unrelated participants, five being novel. The novel C1162T mutation occurred in four white South Africans sharing a common haplotype, suggesting a founder effect. Compound heterozygotes exhibited a severe phenotype signifying an allele dose effect. ARVC is associated with early mortality that is no different to the general South Africa population whose lifespan is shortened by HIV/AIDS. PKP2 gene mutations are common, have an allele dose effect, and a novel founder effect in white South Africans.

Angiotensin-converting enzyme gene polymorphism in arrhythmogenic right ventricular dysplasia: is DD genotype helpful in predicting syncope risk?

Introduction. Arrhythmogenic right ventricular dysplasia (ARVD) is a heritable disorder characterised by fibrofatty replacement of right ventricular myocytes and increased risk of ventricular arrhythmias and sudden cardiac death. Angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism affects myocardialACE levels. DD genotype favours myocardial fibrosis and is associated with malignant ventricular tachycardia.The aim of this study was to explore ACE gene polymorphism inARVD patients.

Methods. Twenty-nine patients with ARVD and 24 controls were included.AllARVD patients had documented sustained ventricular tachycardia. Thirteen patients had syncopal episodes. Six patients were resuscitated from sudden cardiac death.ACE gene polymorphism was identified by polymerase chain reaction technique.

Results. There was no significant difference in DD genotype frequency between ARVD patients and controls (44.8% vs. 45.8%, p=0.94). However, DD genotype frequency was significantly higher in ARVD patients with syncopal episodes compared to those without syncope (69.2% vs. 25.0%, p=0.017, odds ratio:6.750,95% confidence interval: 1.318—34.565). DD genotype was detected in higher frequency also in patients with a family history of sudden cardiac death (66.7% vs. 39.1%,p=0.36).

Conclusion. High prevalence of DD genotype in ARVD patients with syncope suggests that ACE I/D polymorphism might be useful in identifying high-risk patients for syncope.

Desmosomal gene evaluation in Boxers with arrhythmogenic right ventricular cardiomyopathy

OBJECTIVE

To sequence the exonic and splice site regions of the 4 desmosomal genes associated with the human form of familial arrhythmogenic right ventricular cardiomyopathy (ARVC) in Boxers with ARVC and identify a causative mutation.

ANIMALS

10 unrelated Boxers with ARVC and 2 unaffected Labrador Retrievers (control dogs).

PROCEDURES

Exonic and splice site regions of the 4 genes encoding the desmosomal proteins plakophilin-2, plakoglobin, desmoplakin, and desmoglein-2 were sequenced. Sequences were compared for nucleotide sequence changes between affected dogs and the published sequences for clinically normal dogs and between affected dogs and the control dogs. Base-pair changes were considered to be causative for ARVC if they were detected in an affected dog but not in unaffected dogs, and if they involved a conserved amino acid and changed that amino acid to one of a different polarity, acid-base status, or structure.

RESULTS

A causative mutation for ARVC in Boxers was not identified, although single nucleotide polymorphisms were detected in some affected dogs within exon 3 of the plakophilin-2 gene; exon 3 of the plakoglobin gene; exons 3 and 7 of the desmoglein-2 gene; and exons 6, 14, 15, and 24 of the desmoplakin gene. None of these changed the amino acid of the respective protein.

CONCLUSIONS AND CLINICAL RELEVANCE

Mutations within the desmosomal genes associated with the development of ARVC in humans do not appear to be causative for ARVC in Boxers. Genomewide scanning for genetic loci of interest in dogs should be pursued.