Marcel Mannens

Absence of Calsequestrin 2 Causes Severe Forms of Catecholaminergic Polymorphic Ventricular Tachycardia

Abstract— Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare arrhythmogenic disorder characterized by syncopal events and sudden cardiac death at a young age during physical stress or emotion, in the absence of structural heart disease. We report the first nonsense mutations in the cardiac calsequestrin gene, CASQ2, in three CPVT families. The three mutations, a nonsense R33X, a splicing 532+1 G>A, and a 1-bp deletion, 62delA, are thought to induce premature stop codons. Two patients who experienced syncopes before the age of 7 years were homozygous carriers, suggesting a complete absence of calsequestrin 2. One patient was heterozygous for the stop codon and experienced syncopes from the age of 11 years. Despite the different mutations, there is little phenotypic variation of CPVT for the CASQ2 mutations. Of the 16 heterozygous carriers of these various mutations, 14 were devoid of clinical symptoms or ECG anomalies, whereas 2 of them had ventricular arrhythmias at ECG on exercise tests. In line with this, the diagnosis of the probands was difficult because of the absence of a positive family history. In conclusion, these additional three CASQ2 CPVT families suggest that CASQ2 mutations are more common than previously thought and produce a severe form of CPVT. The full text of this article is available at http://www.circresaha.org.

The Human Chitotriosidase Gene NATURE OF INHERITED ENZYME DEFICIENCY

The human chitinase, named chitotriosidase, is a member of family 18 of glycosylhydrolases. Following the cloning of the chitotriosidase cDNA (Boot, R. G., Renkema, G. H., Strijland, A., van Zonneveld, A. J., and Aerts, J. M. F. G. (1995) J. Biol. Chem. 270, 26252–26256), the gene and mRNA have been investigated. The chitotriosidase gene is assigned to chromosome 1q31-q32. The gene consists of 12 exons and spans about 20 kilobases. The nature of the common deficiency in chitotriosidase activity is reported. A 24-base pair duplication in exon 10 results in activation of a cryptic 3′ splice site, generating a mRNA with an in-frame deletion of 87 nucleotides. All chitotriosidase-deficient individuals tested were homozygous for the duplication. The observed carrier frequency of about 35% indicates that the duplication is the predominant cause of chitotriosidase deficiency. The presence of the duplication in individuals from various ethnic groups suggests that this mutation is relatively old.

Plakophilin-2 Mutations Are the Major Determinant of Familial Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy

Background— Mutations in the plakophilin-2 gene (PKP2) have been found in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVC). Hence, genetic screening can potentially be a valuable tool in the diagnostic workup of patients with ARVC. Methods and Results— To establish the prevalence and character of PKP2 mutations and to study potential differences in the associated phenotype, we evaluated 96 index patients, including 56 who fulfilled the published task force criteria. In addition, 114 family members from 34 of these 56 ARVC index patients were phenotyped. In 24 of these 56 ARVC patients (43%), 14 different (11 novel) PKP2 mutations were identified. Four different mutations were found more than once; haplotype analyses revealed identical haplotypes in the different mutation carriers, suggesting founder mutations. No specific genotype–phenotype correlations could be identified, except that negative T waves in V2 and V3 occurred more often in PKP2 mutation carriers (P<0.05). Of the 34 index patients whose family members were phenotyped, 23 familial cases were identified. PKP2 mutations were identified in 16 of these 23 ARVC index patients (70%) with familial ARVC. On the other hand, no PKP2 mutations at all were found in 11 probands without additional affected family members (P<0.001). Conclusions— PKP2 mutations can be identified in nearly half of the Dutch patients fulfilling the ARVC criteria. In familial ARVC, even the vast majority (70%) is caused by PKP2 mutations. However, nonfamilial ARVC is not related to PKP2. The high yield of mutational analysis in familial ARVC is unique in inherited cardiomyopathies.

Catecholaminergic polymorphic ventricular tachycardia : RYR2 mutations, bradycardia, and follow up of the patients

Background: The aim of the study was to assess underlying genetic cause(s), clinical features, and response to therapy in catecholaminergic polymorphic ventricular tachycardia (CPVT) probands. Methods and results: We identified 13 missense mutations in the cardiac ryanodine receptor (RYR2) in 12 probands with CPVT. Twelve were new, of which two are de novo mutations. A further 11 patients were silent gene carriers, suggesting that some mutations are associated with low penetrance. A marked resting sinus bradycardia off drugs was observed in all carriers. On β blocker treatment, 98% of the RYR2 mutation carriers remained symptom free with a median follow up of 2 (range: 2–37) years. Conclusion: CPVT patients with RYR2 mutation have bradycardia regardless of the site of the mutation, which could direct molecular diagnosis in (young) patients without structural heart disease presenting with syncopal events and a slow heart rate but with normal QTc at resting ECG. Treatment with β blockers has been very effective in our CPVT patients during initial or short term follow up. Given the risk of sudden death and the efficacy of β blocker therapy, the identification of large numbers of RYR2 mutations thus calls for genetic screening, early diagnosis, and subsequent preventive strategies.

The RYR2-Encoded Ryanodine Receptor/Calcium Release Channel in Patients Diagnosed Previously With Either Catecholaminergic Polymorphic Ventricular Tachycardia or Genotype Negative, Exercise-Induced Long QT Syndrome: A Comprehensive Open Reading Frame Mutational Analysis

OBJECTIVES This study was undertaken to determine the spectrum and prevalence of mutations in the RYR2-encoded cardiac ryanodine receptor in cases with exertional syncope and normal corrected QT interval (QTc). BACKGROUND Mutations in RYR2 cause type 1 catecholaminergic polymorphic ventricular tachycardia (CPVT1), a cardiac channelopathy with increased propensity for lethal ventricular dysrhythmias. Most RYR2 mutational analyses target 3 canonical domains encoded by <40% of the translated exons. The extent of CPVT1-associated mutations localizing outside of these domains remains unknown as RYR2 has not been examined comprehensively in most patient cohorts. METHODS Mutational analysis of all RYR2 exons was performed using polymerase chain reaction, high-performance liquid chromatography, and deoxyribonucleic acid sequencing on 155 unrelated patients (49% females, 96% Caucasian, age at diagnosis 20 +/- 15 years, mean QTc 428 +/- 29 ms), with either clinical diagnosis of CPVT (n = 110) or an initial diagnosis of exercise-induced long QT syndrome but with QTc <480 ms and a subsequent negative long QT syndrome genetic test (n = 45). RESULTS Sixty-three (34 novel) possible CPVT1-associated mutations, absent in 400 reference alleles, were detected in 73 unrelated patients (47%). Thirteen new mutation-containing exons were identified. Two-thirds of the CPVT1-positive patients had mutations that localized to 1 of 16 exons. CONCLUSIONS Possible CPVT1 mutations in RYR2 were identified in nearly one-half of this cohort; 45 of the 105 translated exons are now known to host possible mutations. Considering that approximately 65% of CPVT1-positive cases would be discovered by selective analysis of 16 exons, a tiered targeting strategy for CPVT genetic testing should be considered.

CONCOR, an initiative towards a national registry and DNA-bank of patients with congenital heart disease in the Netherlands: Rationale, design, and first results

Introduction:Survival of patients with congenital heart disease has dramatically improved after surgical repair became available 40 years ago. Instead of a mortality of 85% during childhood following the natural course, over 85% of these infants are now expected to reach adulthood. However, data on long-term outcome is scarce due to the lack of large, national registries. Moreover, little is known about the genetic basis of congenital heart defects. In 2000, the Interuniversity Cardiology Institute of the Netherlands and the Netherlands Heart Foundation have taken the initiative to develop a national registry and DNA-bank of patients with congenital heart disease in the Netherlands named CONCOR.Objectives: The aims of the CONCOR-project are to facilitate investigation of the prevalence and long-term outcome of specific congenital heart defects and their treatment, to develop an efficient organisational structure for the improvement of healthcare for patients with congenital heart disease, and to allow investigation of the molecular basis of congenital heart defects. Methods: After informed consent, research nurses enter data of participating patients into the CONCOR database using a web application. Data is transferred over the Internet via a secure connection. About 20 ml blood is withdrawn from the patient, and the DNA is isolated and stored. From each participating patient family history on congenital heart disease is obtained. Results: Within two and a half years more than 4200 patients have agreed to participate. More than 99% of the patients that were asked have given their consent to participate in CONCOR. From 60% of these patients DNA has already been obtained. Mean age of the patients included is 34 years; more than 85% of the patients are younger than 45 years. Late complications occur frequently and the incidence increases with advancing age. 18% of the patients are known with supraventricular or ventricular arrhythmias. 2% of the included patients suffered a cerebrovascular accident, 139 (3%) had endocarditis. 6% of the patients has pulmonary hypertension or Eisenmenger syndrome. More than 15% of the patients reported an affected family member with congenital heart disease in the first, second, or third degree. 6% has an affected first-degree relative, and 4% a second-degree relative. Already 10 research projects have started using the CONCOR data and DNA. Conclusion: The population of patients with congenital heart disease is young and rapidly growing. Late complications occur frequently and the incidence increases with advances age. The CONCOR registry and DNA-bank facilitates research on prevalence and long-term outcome and allows investigation of the molecular basis of congenital heart disease.

Mutations in CCBE1 cause generalized lymph vessel dysplasia in humans

Lymphedema, lymphangiectasias, mental retardation and unusual facial characteristics define the autosomal recessive Hennekam syndrome. Homozygosity mapping identified a critical chromosomal region containing CCBE1, the human ortholog of a gene essential for lymphangiogenesis in zebrafish. Homozygous and compound heterozygous mutations in seven subjects paired with functional analysis in a zebrafish model identify CCBE1 as one of few genes causing primary generalized lymph-vessel dysplasia in humans.

Hypomethylation at multiple maternally methylated imprinted regions including PLAGL1 and GNAS loci in Beckwith–Wiedemann syndrome

Genomic imprinting is an epigenetic phenomenon restricting gene expression in a manner dependent on parent of origin. Imprinted gene products are critical regulators of growth and development, and imprinting disorders are associated with both genetic and epigenetic mutations, including disruption of DNA methylation within the imprinting control regions (ICRs) of these genes. It was recently reported that some patients with imprinting disorders have a more generalised imprinting defect, with hypomethylation at a range of maternally methylated ICRs. We report a cohort of 149 patients with a clinical diagnosis of Beckwith–Wiedemann syndrome (BWS), including 81 with maternal hypomethylation of the KCNQ1OT1 ICR. Methylation analysis of 11 ICRs in these patients showed that hypomethylation affecting multiple imprinted loci was restricted to 17 patients with hypomethylation of the KCNQ1OT1 ICR, and involved only maternally methylated loci. Both partial and complete hypomethylation was demonstrated in these cases, suggesting a possible postzygotic origin of a mosaic imprinting error. Some ICRs, including the PLAGL1 and GNAS/NESPAS ICRs implicated in the aetiology of transient neonatal diabetes and pseudohypoparathyroidism type 1b, respectively, were more frequently affected than others. Although we did not find any evidence for mutation of the candidate gene DNMT3L, these results support the hypotheses that trans-acting factors affect the somatic maintenance of imprinting at multiple maternally methylated loci and that the clinical presentation of these complex cases may reflect the loci and tissues affected with the epigenetic abnormalities.

Hypomethylation of the H19 Gene Causes Not Only Silver-Russell Syndrome (SRS) but Also Isolated Asymmetry or an SRS-Like Phenotype

The H19 differentially methylated region (DMR) controls the allele-specific expression of both the imprinted H19 tumor-suppressor gene and the IGF2 growth factor. Hypermethylation of this DMR--and subsequently of the H19 promoter region--is a major cause of the clinical features of gigantism and/or asymmetry seen in Beckwith-Wiedemann syndrome or in isolated hemihypertrophy. Here, we report a series of patients with hypomethylation of the H19 locus. Their main clinical features of asymmetry and growth retardation are the opposite of those seen in patients with hypermethylation of this region. In addition, we show that complete hypomethylation of the H19 promoter is found in two of three patients with the full clinical spectrum of Silver-Russell syndrome. This syndrome is also characterized by growth retardation and asymmetry, among other clinical features. We conclude that patients with these clinical features should be analyzed for H19 hypomethylation.

Human SCN5A gene mutations alter cardiac sodium channel kinetics and are associated with the Brugada syndrome.

BACKGROUND Primary dysrhythmias other than those associated with the long QT syndrome, are increasingly recognized. One of these are represented by patients with a history of resuscitation from cardiac arrest but without any structural heart disease. These patients exhibit a distinct electrocardiographic (ECG) pattern consisting of a persistent ST-segment elevation in the right precordial leads often but not always accompanied by a right bundle branch block (Brugada syndrome). This syndrome is associated with a high mortality rate and has been shown to display familial occurrence. METHODS AND RESULTS Pharmacological sodium channel blockade elicits or worsens the electrocardiographic features associated with this syndrome. Hence, a candidate gene approach directed towards SCN5A, the gene encoding the alpha-subunit of the cardiac sodium channel, was followed in six affected individuals. In two patients missense mutations were identified in the coding region of the gene: R1512W in the DIII-DIV cytoplasmic linker and A1924T in the C-terminal cytoplasmic domain. In two other patients mutations were detected near intron/exon junctions. To assess the functional consequences of the R1512W and A1924T mutations, wild-type and mutant sodium channel proteins were expressed in Xenopus oocytes. Both missense mutations affected channel function, most notably a 4-5 mV negative voltage shift of the steady-state activation and inactivation curves in R1512W and a 9 mV negative voltage shift of the steady-state activation curve in A1924T, measured at 22 degrees C. Recovery from inactivation was slightly prolonged for R1512W channels. The time dependent kinetics of activation and inactivation at -20 mV were not significantly affected by either mutation. CONCLUSIONS Two SCN5A mutations associated with the Brugada syndrome, significantly affect cardiac sodium channel characteristics. The alterations seem to be associated with an increase in inward sodium current during the action potential upstroke.