Genetische identificatie van patiënten en families met lange-QT-syndroom: Grote regionale verschillen in de resultaten van 10 jaar

Objective. To determine the pattern of referral of Dutch patients with a long-QT syndrome (LQTS) on the basis of the postal codes of the LQTS probands from whom blood samples were submitted for DNA diagnostics. Design. Retrospective cohort study. Method. From the databases that are coupled to DNA diagnostics, all index patients were included for whom LQTS diagnostics had been requested during the period 1996-2005 at two clinical genetics centres (the University Medical Centre in Amsterdam and Maastricht University Hospital). The results were related to the postal code of the referred patient and corrected for the number of inhabitants of the region concerned. Results. A total of 421 potential LQTS probands were included. Corrected for the numbers of inhabitants in the various postal codes, the number of referrals varied from 3 per million to no per million inhabitants. In view of the most recent estimated prevalence of LQTS (1:2000), this means that only 15% of the carriers of the LQTS mutation have so far been detected. Conclusion. There were large regional differences in the Netherlands in the requests for DNA diagnostics in patients with clinical LQTS. The overwhelming majority of the LQTS patients in the Netherlands have not yet been referred or identified. Expanding the available courses for general practitioners and cardiologists that are given by the staff of the cardiogenetic centres would seem to be indicated

Long QT syndrome caused by a large duplication in the KCNH2 (HERG) gene undetectable by current polymerase chain reaction-based exon-scanning methodologies

BACKGROUND: The numerous mutations in the long QT syndrome (LQTS)-associated genes reported to date are point mutations or small insertions and deletions in coding regions or at splice junctions. OBJECTIVES: The purpose of this study was to determine the relative copy number of gene exons in a series of mutation-negative LQTS probands. METHODS: We used a quantitative multiplex approach because the polymerase chain reaction (PCR)-based exon-scanning methodologies routinely utilized in mutation analysis are unable to detect large genomic alterations. RESULTS: We identified the first large gene rearrangement consisting of a tandem duplication of 3.7 kb in KCNH2 responsible for LQTS in a Dutch family. This large duplication is expected to lead to nonfunctional or severely debilitated channels, thereby decreasing I(Kr). CONCLUSION: Our findings have implications for genetic testing in the approximately 30% of LQTS patients in whom conventional mutation screening fails to uncover a mutation. Analysis for large gene alterations such as the one described herein in routine genetic testing may provide a genetic diagnosis in a number of these patient

A genetic variants database for arrhythmogenic right ventricular dysplasia/cardiomyopathy

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a hereditary cardiomyopathy characterized by fibrofatty replacement of cardiomyocytes, ventricular tachyarrhythmias and sudden death. ARVD/C is mainly caused by mutations in genes encoding desmosomal proteins. However, the pathogenicity of variants is not always clear. Therefore, we created an online database (www.arvcdatabase.info), providing information on variants in ARVD/C-associated genes. We searched the literature using ARVD/C and its underlying genes as search terms. From the selected papers and our unpublished data, we collected details on the type of mutation and information provided at the protein level. A "details page" contains clinical data and references. To aid the interpretation of missense mutations, we provide data from in silico prediction methods. In May 2009 the database contained 481 variants in eight genes. A total of 144 variants are considered pathogenic, 73 are unknown/unclassified, and 264 have no known pathogenicity. The database was converted into the Leiden Open Variation Database (LOVD) format, a gene-centered collection of DNA variations. The ARVD/C database will be useful for both researchers and clinicians. It can be searched to determine if variants have been published and whether they are considered pathogenic. External users are invited to add information to improve the quantity and quality of the data entere

Long-QT mutation p.K557E-Kv7.1: dominant-negative suppression of I-Ks, but preserved cAMP-dependent up-regulation

Aims Mutations in KCNQ1, encoding for Kv7.1, the alpha-subunit of the I-Ks channel, cause long-QT syndrome type 1, potentially predisposing patients to ventricular tachyarrhythmias and sudden cardiac death, in particular, during elevated sympathetic tone. Here, we aim at characterizing the p.Lys557Glu (K557E) Kv7.1 mutation, identified in a Dutch kindred, at baseline and during (mimicked) increased adrenergic tone. Methods and results K557E carriers had moderate QTc prolongation that augmented significantly during exercise. I-Ks characteristics were determined after co-expressing Kv7.1-wild-type (WT) and/or K557E with minK and Yotiao in Chinese hamster ovary cells. K557E caused I-Ks loss of function with slowing of the activation kinetics, acceleration of deactivation kinetics, and a rightward shift of voltage-dependent activation. Together, these contributed to a dominant-negative reduction in I-Ks density. Confocal microscopy and western blot indicated that trafficking of K557E channels was not impaired. Stimulation of WT I-Ks by 3'-5'-cyclic adenosine monophosphate (cAMP) generated strong current up-regulation that was preserved for K557E in both hetero- and homozygosis. Accumulation of I-Ks at fast rates occurred both in WT and in K557E, but was blunted in the latter. In a computational model, K557E showed a loss of action potential shortening during beta-adrenergic stimulation, in accordance with the lack of QT shortening during exercise in patients. Conclusion K557E causes I-Ks loss of function with reduced fast rate-dependent current accumulation. cAMP-dependent stimulation of mutant I-Ks is preserved, but incapable of fully compensating for the baseline current reduction, explaining the long QT intervals at baseline and the abnormal QT accommodation during exercise in affected patients

On the Pollution of the Irrigation Water

textabstractPURPOSE: Oxidative phosphorylation is under dual genetic control of the nuclear and the mitochondrial DNA (mtDNA). Oxidative phosphorylation disorders are clinically and genetically heterogeneous, which makes it difficult to determine the genetic defect, and symptom-based protocols which link clinical symptoms directly to a specific gene or mtDNA mutation are falling short. Moreover, approximately 25% of the pediatric patients with oxidative phosphorylation disorders is estimated to have mutations in the mtDNA and a standard screening approach for common mutations and deletions will only explain part of these cases. Therefore, we tested a new CHIP-based screening method for the mtDNA. METHODS: MitoChip (Affymetrix) resequencing was performed on three test samples and on 28 patient samples. RESULTS: Call rates were 94% on average and heteroplasmy detection levels varied from 5-50%. A genetic diagnosis can be made in almost one-quarter of the patients at a potential output of 8 complete mtDNA sequences every 4 days. Moreover, a number of potentially pathogenic unclassified variants (UV) were detected. CONCLUSIONS: The availability of long-range PCR protocols and the predominance of single nucleotide substitutions in the mtDNA make the resequencing CHIP a very fast and reliable method to screen the complete mtDNA for mutations