Publications by authors named "Jasper J van der Smagt"

49 Publications

Variants in GNAI1 cause a syndrome associated with variable features including developmental delay, seizures, and hypotonia.

Genet Med 2021 Jan 20. Epub 2021 Jan 20.

Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA, USA.

Purpose: Neurodevelopmental disorders (NDDs) encompass a spectrum of genetically heterogeneous disorders with features that commonly include developmental delay, intellectual disability, and autism spectrum disorders. We sought to delineate the molecular and phenotypic spectrum of a novel neurodevelopmental disorder caused by variants in the GNAI1 gene.

Methods: Through large cohort trio-based exome sequencing and international data-sharing, we identified 24 unrelated individuals with NDD phenotypes and a variant in GNAI1, which encodes the inhibitory Gαi1 subunit of heterotrimeric G-proteins. We collected detailed genotype and phenotype information for each affected individual.

Results: We identified 16 unique variants in GNAI1 in 24 affected individuals; 23 occurred de novo and 1 was inherited from a mosaic parent. Most affected individuals have a severe neurodevelopmental disorder. Core features include global developmental delay, intellectual disability, hypotonia, and epilepsy.

Conclusion: This collaboration establishes GNAI1 variants as a cause of NDDs. GNAI1-related NDD is most often characterized by severe to profound delays, hypotonia, epilepsy that ranges from self-limiting to intractable, behavior problems, and variable mild dysmorphic features.
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http://dx.doi.org/10.1038/s41436-020-01076-8DOI Listing
January 2021

Genetic Evaluation in a Cohort of 126 Dutch Pulmonary Arterial Hypertension Patients.

Genes (Basel) 2020 Oct 13;11(10). Epub 2020 Oct 13.

Department of Clinical Genetics, Amsterdam UMC (location VUmc), 1081HV Amsterdam, The Netherlands.

Pulmonary arterial hypertension (PAH) is a severe, life-threatening disease, and in some cases is caused by genetic defects. This study sought to assess the diagnostic yield of genetic testing in a Dutch cohort of 126 PAH patients. Historically, genetic testing in the Netherlands consisted of the analysis of BMPR2 and SMAD9. These genes were analyzed in 70 of the 126 patients. A (likely) pathogenic (LP/P) variant was detected in 22 (31%) of them. After the identification of additional PAH associated genes, a next generation sequencing (NGS) panel consisting of 19 genes was developed in 2018. Additional genetic testing was offered to the 48 and negative patients, out of which 28 opted for NGS analysis. In addition, this gene panel was analyzed in 56 newly identified idiopathic (IPAH) or pulmonary veno occlusive disease (PVOD) patients. In these 84 patients, NGS panel testing revealed LP/P variants in BMPR2 ( = 4), GDF2 ( = 2), EIF2AK4 ( = 1), and TBX4 ( = 3). Furthermore, 134 relatives of 32 probands with a LP/P variant were tested, yielding 41 carriers. NGS panel screening offered to IPAH/PVOD patients led to the identification of LP/P variants in GDF2, EIF2AK4, and TBX4 in six additional patients. The identification of LP/P variants in patients allows for screening of at-risk relatives, enabling the early identification of PAH.
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http://dx.doi.org/10.3390/genes11101191DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7602048PMC
October 2020

Recessive null-allele variants in MAG associated with spastic ataxia, nystagmus, neuropathy, and dystonia.

Parkinsonism Relat Disord 2020 08 29;77:70-75. Epub 2020 Jun 29.

Institute of Neurogenomics, Helmholtz Zentrum München, Munich, Germany; Institute of Human Genetics, Technical University of Munich, Munich, Germany; Lehrstuhl für Neurogenetik, Technische Universität München, Munich, Germany; Munich Cluster for Systems Neurology, SyNergy, Munich, Germany.

Introduction: The gene encoding myelin-associated glycoprotein (MAG) has been implicated in autosomal-recessive spastic paraplegia type 75. To date, only four families with biallelic missense variants in MAG have been reported. The genotypic and phenotypic spectrum of MAG-associated disease awaits further elucidation.

Methods: Four unrelated patients with complex neurologic conditions underwent whole-exome sequencing within research or diagnostic settings. Following determination of the underlying genetic defects, in-depth phenotyping and literature review were performed.

Results: In all case subjects, we detected ultra-rare homozygous or compound heterozygous variants in MAG. The observed nonsense (c.693C > A [p.Tyr231*], c.980G > A [p.Trp327*], c.1126C > T [p.Gln376*], and 1522C > T [p.Arg508*]) and frameshift (c.517_521dupAGCTG [p.Trp174*]) alleles were predicted to result in premature termination of protein translation. Affected patients presented with variable combinations of psychomotor delay, ataxia, eye movement abnormalities, spasticity, dystonia, and neuropathic symptoms. Cerebellar signs, nystagmus, and pyramidal tract dysfunction emerged as unifying features in the majority of MAG-mutated individuals identified to date.

Conclusions: Our study is the first to describe biallelic null variants in MAG, confirming that loss of myelin-associated glycoprotein causes severe infancy-onset disease with central and peripheral nervous system involvement.
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http://dx.doi.org/10.1016/j.parkreldis.2020.06.027DOI Listing
August 2020

Characterization of SETD1A haploinsufficiency in humans and Drosophila defines a novel neurodevelopmental syndrome.

Mol Psychiatry 2020 Apr 28. Epub 2020 Apr 28.

Department of Human Genetics, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands.

Defects in histone methyltransferases (HMTs) are major contributing factors in neurodevelopmental disorders (NDDs). Heterozygous variants of SETD1A involved in histone H3 lysine 4 (H3K4) methylation were previously identified in individuals with schizophrenia. Here, we define the clinical features of the Mendelian syndrome associated with haploinsufficiency of SETD1A by investigating 15 predominantly pediatric individuals who all have de novo SETD1A variants. These individuals present with a core set of symptoms comprising global developmental delay and/or intellectual disability, subtle facial dysmorphisms, behavioral and psychiatric problems. We examined cellular phenotypes in three patient-derived lymphoblastoid cell lines with three variants: p.Gly535Alafs*12, c.4582-2_4582delAG, and p.Tyr1499Asp. These patient cell lines displayed DNA damage repair defects that were comparable to previously observed RNAi-mediated depletion of SETD1A. This suggested that these variants, including the p.Tyr1499Asp in the catalytic SET domain, behave as loss-of-function (LoF) alleles. Previous studies demonstrated a role for SETD1A in cell cycle control and differentiation. However, individuals with SETD1A variants do not show major structural brain defects or severe microcephaly, suggesting that defective proliferation and differentiation of neural progenitors is unlikely the single underlying cause of the disorder. We show here that the Drosophila melanogaster SETD1A orthologue is required in postmitotic neurons of the fly brain for normal memory, suggesting a role in post development neuronal function. Together, this study defines a neurodevelopmental disorder caused by dominant de novo LoF variants in SETD1A and further supports a role for H3K4 methyltransferases in the regulation of neuronal processes underlying normal cognitive functioning.
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http://dx.doi.org/10.1038/s41380-020-0725-5DOI Listing
April 2020

Pulmonary Fibrosis and a TERT Founder Mutation With a Latency Period of 300 Years.

Chest 2020 Aug 19;158(2):612-619. Epub 2020 Apr 19.

Department of Pulmonology, ILD Center of Excellence, St Antonius Hospital, Nieuwegein; Division of Heart and Lungs, University Medical Center Utrecht, Utrecht, The Netherlands.

Background: Germline mutations in the gene encoding TERT cause haploinsufficiency with subsequent telomere shortening. TERT mutations are associated with short telomere syndromes, such as pulmonary fibrosis (PF), which is often the first manifestation of a short telomere syndrome. Telomere length is heritable, and progeny of telomerase mutation carriers are known to have shorter telomeres. In families with TERT mutations, genetic anticipation, the earlier onset of symptoms with successive generation, is described. Little is known on the number of generations that may pass before disease occurs in families with a TERT mutation.

Research Question: The objective of this study was to determine classification and origin of the new TERT c.2005T mutation from population genetics and genealogic data and disease history of affected families.

Study Design And Methods: The TERT gene of 240 patients with familial PF was screened for mutations. Additionally, 1,015 patients with PF, 1,237 patients with an interstitial lung disease (ILD) without PF, and 529 healthy control subjects were genotyped for the TERT c.2005C>T mutation. Genealogic research was performed on all patients who carried the TERT c.2005T mutation.

Results: We detected the TERT c.2005T (p.Arg669Trp) mutation in 13 out of 1,255 patients with PF vs none of the patients with ILD without PF and the healthy control subjects. Genealogic research connected four of the TERT c.2005T mutation carriers to a common ancestor who lived seven generations back, spanning a period of 300 years.

Interpretation: The TERT c.2005T mutation is a pathogenic mutation and associates with PF. This study learns that a latency period of > 300 years may pass before the cumulative effect of telomere shortening eventually leads to PF. This finding underlines the complexity of the clinical interpretation of TERT mutations because, not the presence of the mutation, but the result of genetic anticipation, is associated with disease. Therefore, multidisciplinary discussion between pulmonary physicians, clinical geneticists, and genetic laboratory experts is recommended.
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http://dx.doi.org/10.1016/j.chest.2020.03.069DOI Listing
August 2020

Pulmonary fibrosis linked to variants in the gene, encoding the telomere protein TPP1.

Eur Respir J 2019 12 19;54(6). Epub 2019 Dec 19.

Dept of Pulmonology, Interstitial Lung Diseases Center of Excellence, St Antonius Hospital, Nieuwegein, The Netherlands

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http://dx.doi.org/10.1183/13993003.00809-2019DOI Listing
December 2019

Arrhythmogenic Right Ventricular Cardiomyopathy-Associated Desmosomal Variants Are Rarely De Novo.

Circ Genom Precis Med 2019 08 6;12(8):e002467. Epub 2019 Aug 6.

Amsterdam UMC, University of Amsterdam, Department of Clinical Genetics, the Netherlands (F.H.M.v.L., R.Z., R.H.L.D., J.P.v.T., C.A.J.).

Background: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is associated with pathogenic/likely pathogenic (P/LP) variants in genes encoding the cardiac desmosomal proteins. Origin of these variants, including de novo mutation rate and extent of founder versus recurrent variants has implications for variant adjudication and clinical care, yet this has never been systematically investigated.

Methods: We identified arrhythmogenic right ventricular cardiomyopathy probands who met 2010 Task Force Criteria and had undergone genotyping that included sequencing of the desmosomal genes (PKP2, DSP, DSG2, DSC2, and JUP) from 3 arrhythmogenic right ventricular cardiomyopathy registries in America and Europe. We classified the desmosomal variants, defined the contribution of unique versus nonunique (ie, not family-specific) P/LP variants, and identified the frequency and characteristics of de novo variants. Next, we haplotyped nonunique variants to determine how often they likely represent a single mutation event in a common ancestor (implied by shared haplotypes) versus multiple mutation events at the same genetic location.

Results: Of 501 arrhythmogenic right ventricular cardiomyopathy probands, 322 (64.3%) carried 327 desmosomal P/LP variants. Most variants (n=247, 75.6%, in 245 patients) were identified in more than one proband and, therefore, considered nonunique. For 212/327 variants (64.8%) genetic cascade screening was performed extensively enough to identify the parental origin of the P/LP variant. Only 3 variants were de novo, 2 of which were whole gene deletions. For 24 nonunique P/LP PKP2 variants, haplotyping was conducted in 183 available families. For all 24 variants, multiple seemingly unrelated families sharing identical haplotypes were identified, suggesting that these variants originate from common founders.

Conclusions: Most desmosomal P/LP variants are inherited, nonunique, and originate from ancient founders. Two of 3 de novo variants were large deletions. These observations inform genetic testing, cascade screening, and variant adjudication.
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http://dx.doi.org/10.1161/CIRCGEN.119.002467DOI Listing
August 2019

Lack of genotype-phenotype correlation in basal cell nevus syndrome: A Dutch multicenter retrospective cohort study.

J Am Acad Dermatol 2020 Aug 30;83(2):604-607. Epub 2019 Jul 30.

Department of Dermatology, Maastricht University Medical Centre; GROW Research Institute for Oncology and Developmental Biology, Maastricht University.

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http://dx.doi.org/10.1016/j.jaad.2019.07.072DOI Listing
August 2020

Correction: IQSEC2-related encephalopathy in males and females: a comparative study including 37 novel patients.

Genet Med 2019 Aug;21(8):1897-1898

INSERM, U 1127, CNRS UMR 7225, Sorbonne Universites, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle epiniere, ICM, Paris, France.

This Article was originally published under Nature Research's License to Publish, but has now been made available under a CC BY 4.0 license. The PDF and HTML versions of the Article have been modified accordingly.
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http://dx.doi.org/10.1038/s41436-018-0327-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7608434PMC
August 2019

IQSEC2-related encephalopathy in males and females: a comparative study including 37 novel patients.

Genet Med 2019 04 12;21(4):837-849. Epub 2018 Sep 12.

INSERM, U 1127, CNRS UMR 7225, Sorbonne Universites, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle epiniere, ICM, Paris, France.

Purpose: Variants in IQSEC2, escaping X inactivation, cause X-linked intellectual disability with frequent epilepsy in males and females. We aimed to investigate sex-specific differences.

Methods: We collected the data of 37 unpublished patients (18 males and 19 females) with IQSEC2 pathogenic variants and 5 individuals with variants of unknown significance and reviewed published variants. We compared variant types and phenotypes in males and females and performed an analysis of IQSEC2 isoforms.

Results: IQSEC2 pathogenic variants mainly led to premature truncation and were scattered throughout the longest brain-specific isoform, encoding the synaptic IQSEC2/BRAG1 protein. Variants occurred de novo in females but were either de novo (2/3) or inherited (1/3) in males, with missense variants being predominantly inherited. Developmental delay and intellectual disability were overall more severe in males than in females. Likewise, seizures were more frequently observed and intractable, and started earlier in males than in females. No correlation was observed between the age at seizure onset and severity of intellectual disability or resistance to antiepileptic treatments.

Conclusion: This study provides a comprehensive overview of IQSEC2-related encephalopathy in males and females, and suggests that an accurate dosage of IQSEC2 at the synapse is crucial during normal brain development.
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http://dx.doi.org/10.1038/s41436-018-0268-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6752297PMC
April 2019

Haploinsufficiency of CUX1 Causes Nonsyndromic Global Developmental Delay With Possible Catch-up Development.

Ann Neurol 2018 08 31;84(2):200-207. Epub 2018 Aug 31.

Institute of Human Genetics, University of Leipzig Hospitals and Clinics, Leipzig, Germany.

Objective: Developmental delay (DD) with favorable intellectual outcome and mild intellectual disability (ID) are mostly considered to be of complex genetic and environmental origin, but, in fact, often remain unclear. We aimed at proving our assumption that also mild cases of DD and ID may be of monogenic etiology.

Methods: We clinically evaluated 8 individuals and performed exome sequencing or array copy number analysis and identified variants in CUX1 as the likely cause. In addition, we included a case from the public database, DECIPHER.

Results: All 9 individuals harbored heterozygous null-allele variants in CUX1, encoding the Cut-homeobox 1 transcription factor that is involved in regulation of dendritogenesis and cortical synapse formation in layer II to IV cortical neurons. Six variants arose de novo, while in one family the variant segregated with ID. Of the 9 included individuals, 2 were diagnosed with moderate ID, 3 with mild ID, and 3 showed a normal age-related intelligence at ages 4, 6, and 8 years after a previous history of significant DD.

Interpretation: Our results suggest that null-allele variants, and thus haploinsufficiency of CUX1, cause an isolated phenotype of DD or ID with possible catch-up development. This illustrates that such a developmental course is not necessarily genetic complex, but may also be attributed to a monogenic cause. Ann Neurol 2018;84:200-207.
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http://dx.doi.org/10.1002/ana.25278DOI Listing
August 2018

Lack of evidence for a causal role of CALR3 in monogenic cardiomyopathy.

Eur J Hum Genet 2018 11 9;26(11):1603-1610. Epub 2018 Jul 9.

Department of Clinical Genetics, Erasmus University Medical Center, Rotterdam, The Netherlands.

The pathogenicity of previously published disease-associated genes and variants is sometimes questionable. Large-scale, population-based sequencing studies have uncovered numerous false assignments of pathogenicity. Misinterpretation of sequence variants may have serious implications for the patients and families involved, as genetic test results are increasingly being used in medical decision making. In this study, we assessed the role of the calreticulin-3 gene (CALR3) in cardiomyopathy. CALR3 has been included in several cardiomyopathy gene panels worldwide. Its inclusion is based on a single publication describing two missense variants in patients with hypertrophic cardiomyopathy. In our national cardiomyopathy cohort (n = 6154), we identified 17 unique, rare heterozygous CALR3 variants in 48 probands. Overall, our patient cohort contained a significantly higher number of rare CALR3 variants compared to the ExAC population (p = 0.0036). However, after removing a potential Dutch founder variant, no statistically significant difference was found (p = 0.89). In nine probands, the CALR3 variant was accompanied by a disease-causing variant in another, well-known cardiomyopathy gene. In three families, the CALR3 variant did not segregate with the disease. Furthermore, we could not demonstrate calreticulin-3 protein expression in myocardial tissues at various ages. On the basis of these findings, it seems highly questionable that variants in CALR3 are a monogenic cause of cardiomyopathy.
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http://dx.doi.org/10.1038/s41431-018-0208-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6189092PMC
November 2018

Juvenile interleukin-36 receptor antagonist deficiency (DITRA) with c.80T>C (p.Leu27Pro) mutation successfully treated with etanercept and acitretin.

JAAD Case Rep 2018 Mar 2;4(2):192-195. Epub 2018 Feb 2.

Department of Dermatology, Sophia Children's Hospital, Erasmus MC University Medical Centre Rotterdam, Rotterdam, The Netherlands.

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http://dx.doi.org/10.1016/j.jdcr.2017.08.019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5993535PMC
March 2018

Autosomal recessive Noonan syndrome associated with biallelic LZTR1 variants.

Genet Med 2018 10 22;20(10):1175-1185. Epub 2018 Feb 22.

Medical Genomics and Metabolic Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, USA.

Purpose: To characterize the molecular genetics of autosomal recessive Noonan syndrome.

Methods: Families underwent phenotyping for features of Noonan syndrome in children and their parents. Two multiplex families underwent linkage analysis. Exome, genome, or multigene panel sequencing was used to identify variants. The molecular consequences of observed splice variants were evaluated by reverse-transcription polymerase chain reaction.

Results: Twelve families with a total of 23 affected children with features of Noonan syndrome were evaluated. The phenotypic range included mildly affected patients, but it was lethal in some, with cardiac disease and leukemia. All of the parents were unaffected. Linkage analysis using a recessive model supported a candidate region in chromosome 22q11, which includes LZTR1, previously shown to harbor mutations in patients with Noonan syndrome inherited in a dominant pattern. Sequencing analyses of 21 live-born patients and a stillbirth identified biallelic pathogenic variants in LZTR1, including putative loss-of-function, missense, and canonical and noncanonical splicing variants in the affected children, with heterozygous, clinically unaffected parents and heterozygous or normal genotypes in unaffected siblings.

Conclusion: These clinical and genetic data confirm the existence of a form of Noonan syndrome that is inherited in an autosomal recessive pattern and identify biallelic mutations in LZTR1.
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http://dx.doi.org/10.1038/gim.2017.249DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6105555PMC
October 2018

-Related Cardiac Disease: Late Onset With a Variable and Mild Phenotype in a Large Cohort of Patients With the Lamin A/C p.(Arg331Gln) Founder Mutation.

Circ Cardiovasc Genet 2017 Aug;10(4)

For the author affiliations, please see the Appendix.

Background: Interpretation of missense variants can be especially difficult when the variant is also found in control populations. This is what we encountered for the c.992G>A (p.(Arg331Gln)) variant. Therefore, to evaluate the effect of this variant, we combined an evaluation of clinical data with functional experiments and morphological studies.

Methods And Results: Clinical data of 23 probands and 35 family members carrying this variant were retrospectively collected. A time-to-event analysis was performed to compare the course of the disease with carriers of other mutations. Myocardial biopsies were studied with electron microscopy and by measuring force development of the sarcomeres. Morphology of the nuclear envelope was assessed with immunofluorescence on cultured fibroblasts. The phenotype in probands and family members was characterized by atrioventricular conduction disturbances (61% and 44%, respectively), supraventricular arrhythmias (69% and 52%, respectively), and dilated cardiomyopathy (74% and 14%, respectively). LMNA p.(Arg331Gln) carriers had a significantly better outcome regarding the composite end point (malignant ventricular arrhythmias, end-stage heart failure, or death) compared with carriers of other pathogenic mutations. A shared haplotype of 1 Mb around suggested a common founder. The combined logarithm of the odds score was 3.46. Force development in membrane-permeabilized cardiomyocytes was reduced because of decreased myofibril density. Structural nuclear -associated envelope abnormalities, that is, blebs, were confirmed by electron microscopy and immunofluorescence microscopy.

Conclusions: Clinical, morphological, functional, haplotype, and segregation data all indicate that LMNA p.(Arg331Gln) is a pathogenic founder mutation with a phenotype reminiscent of other mutations but with a more benign course.
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http://dx.doi.org/10.1161/CIRCGENETICS.116.001631DOI Listing
August 2017

encephalopathy: novel findings on phenotype, variant clustering, functional consequences and treatment aspects.

J Med Genet 2017 07 4;54(7):460-470. Epub 2017 Apr 4.

Institute of Human Genetics, University of Leipzig Hospitals and Clinics, Leipzig, Germany.

Background: We aimed for a comprehensive delineation of genetic, functional and phenotypic aspects of encephalopathy and explored potential prospects of personalised medicine.

Methods: Data of 48 individuals with de novo variants were collected from several diagnostic and research cohorts, as well as from 43 patients from the literature. Functional consequences and response to memantine treatment were investigated in vitro and eventually translated into patient care.

Results: Overall, de novo variants in 86 patients were classified as pathogenic/likely pathogenic. Patients presented with neurodevelopmental disorders and a spectrum of hypotonia, movement disorder, cortical visual impairment, cerebral volume loss and epilepsy. Six patients presented with a consistent malformation of cortical development (MCD) intermediate between tubulinopathies and polymicrogyria. Missense variants cluster in transmembrane segments and ligand-binding sites. Functional consequences of variants were diverse, revealing various potential gain-of-function and loss-of-function mechanisms and a retained sensitivity to the use-dependent blocker memantine. However, an objectifiable beneficial treatment response in the respective patients still remains to be demonstrated.

Conclusions: In addition to previously known features of intellectual disability, epilepsy and autism, we found evidence that encephalopathy is also frequently associated with movement disorder, cortical visual impairment and MCD revealing novel phenotypic consequences of channelopathies.
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http://dx.doi.org/10.1136/jmedgenet-2016-104509DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5656050PMC
July 2017

Distinct fibrosis pattern in desmosomal and phospholamban mutation carriers in hereditary cardiomyopathies.

Heart Rhythm 2017 07 30;14(7):1024-1032. Epub 2017 Mar 30.

Department of Pathology, University Medical Center Utrecht, Utrecht, the Netherlands. Electronic address:

Background: Desmosomal and phospholamban (PLN) mutations are associated with arrhythmogenic cardiomyopathy. Ultimately, most cardiomyopathic hearts develop significant cardiac fibrosis.

Objective: To compare the fibrosis patterns of desmosomal and p. Arg14del PLN-associated cardiomyopathies with the pattern in hearts with other hereditary cardiomyopathies.

Methods: A midventricular transversal slice was obtained from hearts of 30 patients with a cardiomyopathy with a known underlying mutation and from 8 controls. Fibrosis and fatty changes were quantitatively analyzed using digital microscopy.

Results: Hearts from patients with desmosomal mutations (n = 6) showed fibrosis and fibrofatty replacement in the left ventricular (LV) outer myocardium, mainly in the posterolateral wall, and in the right ventricle. A similar phenotype, but with significantly more severe fibrotic changes in the LV, was found in the PLN mutation group (n = 8). Cardiomyopathies associated with lamin A/C (n = 5), sarcomeric (n = 8), and desmin (n = 3) mutations all showed a different pattern from that of the desmosomal and PLN mutation carriers. The posterolateral LV wall appeared to be the most discriminative area with fibrosis and fatty changes predominantly at the outer compact myocardium in 13 of 14 hearts with desmosomal and PLN mutations (93%), in 0 of 13 hearts with lamin A/C and sarcomeric mutations (0%), and in 1 of 3 desminopathic hearts (33%) (P < .001).

Conclusion: Desmosomal- and PLN-associated cardiomyopathies have a fibrosis pattern distinct from the patterns in other hereditary cardiomyopathies. The posterolateral LV wall appeared to be the most discriminative region between mutation groups. These results may provide a roadmap for cardiac imaging interpretation and may help in further unraveling disease mechanisms.
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http://dx.doi.org/10.1016/j.hrthm.2017.03.034DOI Listing
July 2017

Six uneventful pregnancy outcomes in an extended vascular Ehlers-Danlos syndrome family.

Am J Med Genet A 2017 Feb 7;173(2):519-523. Epub 2016 Nov 7.

Department of Cardiology, University Medical Center Utrecht (UMCU), Utrecht, The Netherlands.

Vascular Ehlers-Danlos Syndrome (vEDS) is caused by heterozygous mutations in COL3A1 and is characterized by fragile vasculature and hollow organs, with a high risk of catastrophic events at a young age. During pregnancy and delivery, maternal mortality rates up until 25% have been reported. However, recent pedigree analysis reported a substantial lower pregnancy-related mortality rate of 4.9%. Here, we describe an extended vEDS family with multiple uneventful pregnancy outcomes. In the proband, a 37-year-old woman, DNA-analysis because of an asymptomatic iliac artery dissection revealed a pathogenic mutation in COL3A1 (c.980G>A; p. Gly327Asp). She had had three uneventful vaginal deliveries. At the time of diagnosis, her 33-year-old niece was 25 weeks pregnant. She had had one uneventful vaginal delivery. Targeted DNA-analysis revealed that she was carrier of the COL3A1 mutation. Ultrasound detected an aneurysm in the abdominal aorta with likely a dissection. An uneventful elective cesarean section was performed at a gestational age of 37 weeks. The 40-year-old sister of our proband had had one uneventful vaginal delivery and an active pregnancy wish. Cascade DNA-screening showed her to carry the COL3A1 mutation. Computed Tomography Angiography (CTA) of her aorta revealed a type B dissection with the most proximal entry tear just below the superior mesenteric artery. Pregnancy was therefore discouraged. This familial case illustrates the complexity and challenges of reproductive decision-making in a potentially lethal condition as vEDS, and highlights the importance of a multidisciplinary approach. Moreover, it suggests that previous pregnancy-related risks of vEDS may be overestimated. © 2016 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/ajmg.a.38033DOI Listing
February 2017

Next-generation sequencing of a large gene panel in patients initially diagnosed with idiopathic ventricular fibrillation.

Heart Rhythm 2017 07 11;14(7):1035-1040. Epub 2017 Jan 11.

Department of Cardiology, University Medical Centre, Utrecht, The Netherlands; Department of Internal Medicine and Cardiology, Bergman Clinics, Bilthoven, The Netherlands.

Background: Idiopathic ventricular fibrillation (IVF) is a rare primary cardiac arrhythmia syndrome that is diagnosed in a resuscitated cardiac arrest victim, with documented ventricular fibrillation, in whom no underlying cause is identified after comprehensive clinical evaluation. In some patients, causative genetic mutations are detected that facilitate patient treatment and follow-up. The feasibility of next-generation sequencing (NGS) has increased with its greater availability and decreasing costs.

Objective: The aim of this study was to assess the diagnostic yield of NGS in patients with IVF.

Methods: A total of 33 patients initially diagnosed with IVF were included (mean age 53 ± 15 years; 14(42%) men). In all included patients, NGS of 33 genes and the DPP6 haplotype revealed no pathogenic mutations. Genetic screening comprised NGS of a panel of 179 additional genes. Variants with a minor allele frequency of <0.05% were assessed for pathogenicity by using existing mutation databases and in silico predictive algorithms.

Results: In 1 of 33 patients, a likely pathogenic mutation was detected. The added yield of genetic testing with NGS of 179 additional genes is 3% in patients with IVF. In 15% of patients, 1 or multiple variants of uncertain clinical significance were detected.

Conclusion: The added yield of genetic screening of extended NGS panels in patients initially diagnosed with IVF is minimal. Routine analysis of large diagnostic NGS panels is therefore not recommended.
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http://dx.doi.org/10.1016/j.hrthm.2017.01.010DOI Listing
July 2017

Long-Term Outcome of Patients Initially Diagnosed With Idiopathic Ventricular Fibrillation: A Descriptive Study.

Circ Arrhythm Electrophysiol 2016 10;9(10)

From the Departments of Cardiology (M.V., J.F.v.d.H., P.A.D., P.L., R.J.H.) and Clinical Genetics (J.J.v.d.S.), University Medical Centre, Utrecht, The Netherlands; Department of Internal Medicine and Cardiology, Bergman Clinics, Bilthoven, The Netherlands (M.V., R.J.H.); and Department of Clinical and Experimental Cardiology, Heart Centre, AMC, Amsterdam, The Netherlands (A.A.W.).

Background: Idiopathic ventricular fibrillation (IVF) is a rare cause of sudden cardiac arrest. Limited data are available on the long-term outcome of IVF patients.

Methods And Results: In this retrospective cohort study, 107 consecutive patients with an initial diagnosis of IVF were analyzed (age at index event 40.4 years, 60% male). Missing diagnostic data were acquired during follow-up, including genetic testing, to exclude underlying disease. A specific diagnosis was revealed in 22 of 107 patients (21%) during a median follow-up of 10.2 years. Mortality rate was 9% in IVF patients (8/85). Appropriate implantable cardioverter-defibrillator therapy was delivered in 23 patients (29%) of 78 IVF patients with an implantable cardioverter-defibrillator, with a median of 3 appropriate shocks per patient.

Conclusions: One fifth of the patients initially diagnosed with IVF reveal a specific diagnosis during long-term follow-up. Additional diagnostic testing, including genetic testing, contributes to the detection of specific diseases. The recurrence rate of ventricular arrhythmias in IVF patients is high. Our data show the importance of thorough follow-up and reassessment of diagnosis in IVF patients.
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http://dx.doi.org/10.1161/CIRCEP.116.004258DOI Listing
October 2016

A patient with early repolarization syndrome and concurrent Brugada syndrome: Demonstration of a different pathophysiology?

Int J Cardiol 2016 Nov 5;223:58-60. Epub 2016 Aug 5.

Department of Cardiology, University Medical Centre, Utrecht, the Netherlands; Department of Internal Medicine and Cardiology, Bergman Clinics, Bilthoven, the Netherlands.

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http://dx.doi.org/10.1016/j.ijcard.2016.08.072DOI Listing
November 2016

Biallelic Truncating Mutations in ALPK3 Cause Severe Pediatric Cardiomyopathy.

J Am Coll Cardiol 2016 Feb;67(5):515-25

Department of Clinical Genetics, Erasmus University Medical Center, Rotterdam, the Netherlands.

Background: Cardiomyopathies are usually inherited and predominantly affect adults, but they can also present in childhood. Although our understanding of the molecular basis of pediatric cardiomyopathy has improved, the underlying mechanism remains elusive in a substantial proportion of cases.

Objectives: This study aimed to identify new genes involved in pediatric cardiomyopathy.

Methods: The authors performed homozygosity mapping and whole-exome sequencing in 2 consanguineous families with idiopathic pediatric cardiomyopathy. Sixty unrelated patients with pediatric cardiomyopathy were subsequently screened for mutations in a candidate gene. First-degree relatives were submitted to cardiac screening and cascade genetic testing. Myocardial samples from 2 patients were processed for histological and immunohistochemical studies.

Results: We identified 5 patients from 3 unrelated families with pediatric cardiomyopathy caused by homozygous truncating mutations in ALPK3, a gene encoding a nuclear kinase that plays an essential role in early differentiation of cardiomyocytes. All patients with biallelic mutations presented with severe hypertrophic and/or dilated cardiomyopathy in utero, at birth, or in early childhood. Three patients died from heart failure within the first week of life. Moreover, 2 of 10 (20%) heterozygous family members showed hypertrophic cardiomyopathy with an atypical distribution of hypertrophy. Deficiency of alpha-kinase 3 has previously been associated with features of both hypertrophic and dilated cardiomyopathy in mice. Consistent with studies in knockout mice, we provide microscopic evidence for intercalated disc remodeling.

Conclusions: Biallelic truncating mutations in the newly identified gene ALPK3 give rise to severe, early-onset cardiomyopathy in humans. Our findings highlight the importance of transcription factor pathways in the molecular mechanisms underlying human cardiomyopathies.
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http://dx.doi.org/10.1016/j.jacc.2015.10.093DOI Listing
February 2016

Effectiveness of whole-exome sequencing and costs of the traditional diagnostic trajectory in children with intellectual disability.

Genet Med 2016 09 4;18(9):949-56. Epub 2016 Feb 4.

Department of Genetics, Utrecht University Medical Center, Utrecht, The Netherlands.

Purpose: This study investigated whole-exome sequencing (WES) yield in a subset of intellectually disabled patients referred to our clinical diagnostic center and calculated the total costs of these patients' diagnostic trajectory in order to evaluate early WES implementation.

Methods: We compared 17 patients' trio-WES yield with the retrospective costs of diagnostic procedures by comprehensively examining patient records and collecting resource use information for each patient, beginning with patient admittance and concluding with WES initiation. We calculated cost savings using scenario analyses to evaluate the costs replaced by WES when used as a first diagnostic tool.

Results: WES resulted in diagnostically useful outcomes in 29.4% of patients. The entire traditional diagnostic trajectory average cost was $16,409 per patient, substantially higher than the $3,972 trio-WES cost. WES resulted in average cost savings of $3,547 for genetic and metabolic investigations in diagnosed patients and $1,727 for genetic investigations in undiagnosed patients.

Conclusion: The increased causal variant detection yield by WES and the relatively high costs of the entire traditional diagnostic trajectory suggest that early implementation of WES is a relevant and cost-efficient option in patient diagnostics. This information is crucial for centers considering implementation of WES and serves as input for future value-based research into diagnostics.Genet Med 18 9, 949-956.
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http://dx.doi.org/10.1038/gim.2015.200DOI Listing
September 2016

Germline mutations in RYR1 are associated with foetal akinesia deformation sequence/lethal multiple pterygium syndrome.

Acta Neuropathol Commun 2014 Dec 5;2:148. Epub 2014 Dec 5.

Department of Medical Genetics, University of Cambridge and NIHR Cambridge Biomedical Research Centre, Cambridge Biomedical Campus, Cambridge, CB2 0QQ, UK.

Introduction: Foetal akinesia deformation sequence syndrome (FADS) is a genetically heterogeneous disorder characterised by the combination of foetal akinesia and developmental defects which may include pterygia (joint webbing). Traditionally multiple pterygium syndrome (MPS) has been divided into two forms: prenatally lethal (LMPS) and non-lethal Escobar type (EVMPS) types. Interestingly, FADS, LMPS and EVMPS may be allelic e.g. each of these phenotypes may result from mutations in the foetal acetylcholine receptor gamma subunit gene (CHRNG). Many cases of FADS and MPS do not have a mutation in a known FADS/MPS gene and we undertook molecular genetic studies to identify novel causes of these phenotypes.

Results: After mapping a novel locus for FADS/LMPS to chromosome 19, we identified a homozygous null mutation in the RYR1 gene in a consanguineous kindred with recurrent LMPS pregnancies. Resequencing of RYR1 in a cohort of 66 unrelated probands with FADS/LMPS/EVMPS (36 with FADS/LMPS and 30 with EVMPS) revealed two additional homozygous mutations (in frame deletions). The overall frequency of RYR1 mutations in probands with FADS/LMPS was 8.3%.

Conclusions: Our findings report, for the first time, a homozygous RYR1 null mutation and expand the range of RYR1-related phenotypes to include early lethal FADS/LMPS. We suggest that RYR1 mutation analysis should be performed in cases of severe FADS/LMPS even in the absence of specific histopathological indicators of RYR1-related disease.
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http://dx.doi.org/10.1186/s40478-014-0148-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4271450PMC
December 2014

Monocarboxylate transporter 1 deficiency and ketone utilization.

N Engl J Med 2014 Nov;371(20):1900-7

From the Division of Pediatrics, Department of Metabolic Diseases (P.M.H., G.V.), and the Division of Pediatrics, Department of Pediatric Gastroenterology (R.H.J.H.), Wilhelmina Children's Hospital, and the Center for Molecular Medicine, Department of Medical Genetics (G.R.M., M.J.G., K.D., M.H., B.Z., J.J.S., N.M.V.-D., G.H.), University Medical Center Utrecht, Utrecht, Laboratory Genetic Metabolic Diseases, Departments of Clinical Chemistry and Pediatrics, Academic Medical Center, Amsterdam (S.F., J.P.N.R., M.T., R.J.A.W.), the Division of Pediatrics, Department of Metabolic Diseases, and Laboratory Genetic Metabolic Diseases, Maastricht University Medical Center, Maastricht (M.E.R.-G.), and the Department of Pediatrics, Nijmegen Center for Mitochondrial Disorders, Radboud University Medical Center, Nijmegen (M.C.V.) - all in the Netherlands; the National Centre for Inherited Metabolic Disorders, Children's University Hospital, Dublin, Ireland (A.A.M.); the Department of Pediatric Metabolism and Nutrition, Gazi University School of Medicine, Ankara, Turkey (I.O.); and the Department of Paediatric Metabolic Medicine, Sheffield Children's Hospital, Sheffield (M.J.S.), the Department of Metabolic Medicine, Great Ormond Street Hospital NHS Foundation Trust, London (M.C.), Chemical Pathology, Department of Laboratory Medicine, Salisbury (N.O.), and the Department of Clinical Biochemistry, Southampton General Hospital, Southampton (V.W.) - all in the United Kingdom.

Ketoacidosis is a potentially lethal condition caused by the imbalance between hepatic production and extrahepatic utilization of ketone bodies. We performed exome sequencing in a patient with recurrent, severe ketoacidosis and identified a homozygous frameshift mutation in the gene encoding monocarboxylate transporter 1 (SLC16A1, also called MCT1). Genetic analysis in 96 patients suspected of having ketolytic defects yielded seven additional inactivating mutations in MCT1, both homozygous and heterozygous. Mutational status was found to be correlated with ketoacidosis severity, MCT1 protein levels, and transport capacity. Thus, MCT1 deficiency is a novel cause of profound ketoacidosis; the present work suggests that MCT1-mediated ketone-body transport is needed to maintain acid-base balance.
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http://dx.doi.org/10.1056/NEJMoa1407778DOI Listing
November 2014

Functional assessment of potential splice site variants in arrhythmogenic right ventricular dysplasia/cardiomyopathy.

Heart Rhythm 2014 Nov 31;11(11):2010-7. Epub 2014 Jul 31.

Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address:

Background: Interpretation of genetic screening results in arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) often is difficult. Pathogenicity of variants with uncertain clinical significance may be predicted by software algorithms. However, functional assessment can unambiguously demonstrate the effect of such variants.

Objective: The purpose of this study was to perform functional analysis of potential splice site variants in ARVD/C patients.

Methods: Nine variants in desmosomal (PKP2, JUP, DSG2, DSC2) genes with potential RNA splicing effect were analyzed. The variants were found in patients who fulfilled 2010 ARVD/C Task Force Criteria (n = 7) or had suspected ARVD/C (n = 2). Total RNA was isolated from fresh blood samples and subjected to reverse transcriptase polymerase chain reaction.

Results: An effect on splicing was predicted by software algorithms for all variants. Of the 9 variants, 5 were intronic and 4 exonic. RNA analysis showed a functional effect on mRNA splicing by exon skipping, generation of new splice sites, or activation of cryptic sites in 6 variants. All 5 intronic variants tested severely impaired splicing. Only 1 of 4 exonic potential splice site variants was shown to have a deleterious effect on splicing. The remaining 3 exonic variants had no detectable effect on splicing, and heterozygous presence in mRNA confirmed biallelic expression.

Conclusion: Six variants of uncertain clinical significance in the PKP2, JUP, and DSG2 genes showed a deleterious effect on mRNA splicing, indicating these are ARVD/C-related pathogenic splice site mutations. These results highlight the importance of functional assessment of potential splice site variants to improve patient care and facilitate cascade screening.
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http://dx.doi.org/10.1016/j.hrthm.2014.07.041DOI Listing
November 2014

Targeted phosphotyrosine profiling of glycoprotein VI signaling implicates oligophrenin-1 in platelet filopodia formation.

Arterioscler Thromb Vasc Biol 2013 Jul 25;33(7):1538-43. Epub 2013 Apr 25.

Biomolecular Mass Spectrometry and Proteomics and Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands.

Objective: Platelet adhesion to subendothelial collagen is dependent on the integrin α2β1 and glycoprotein VI (GPVI) receptors. The major signaling routes in collagen-dependent platelet activation are outlined; however, crucial detailed knowledge of the actual phosphorylation events mediating them is still limited. Here, we explore phosphotyrosine signaling events downstream of GPVI with site-specific detail.

Approach And Results: Immunoprecipitations of phosphotyrosine-modified peptides from protein digests of GPVI-activated and resting human platelets were compared by stable isotope-based quantitative mass spectrometry. We surveyed 214 unique phosphotyrosine sites over 2 time points, of which 28 showed a significant increase in phosphorylation on GPVI activation. Among these was Tyr370 of oligophrenin-1 (OPHN1), a Rho GTPase-activating protein. To elucidate the function of OPHN1 in platelets, we performed an array of functional platelet analyses within a small cohort of patients with rare oligophrenia. Because of germline mutations in the OPHN1 gene locus, these patients lack OPHN1 expression entirely and are in essence a human knockout model. Our studies revealed that among other unaltered properties, patients with oligophrenia show normal P-selectin exposure and αIIbβ3 activation in response to GPVI, as well as normal aggregate formation on collagen under shear conditions. Finally, the major difference in OPHN1-deficient platelets turned out to be a significantly reduced collagen-induced filopodia formation.

Conclusions: In-depth phosphotyrosine screening revealed many novel signaling recipients downstream of GPVI activation uncovering a new level of detail within this important pathway. To illustrate the strength of such data, functional follow-up of OPHN1 in human platelets deficient in this protein showed reduced filopodia formation on collagen, an important parameter of platelet hemostatic function.
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http://dx.doi.org/10.1161/ATVBAHA.112.300916DOI Listing
July 2013

Remodeling of the cardiac sodium channel, connexin43, and plakoglobin at the intercalated disk in patients with arrhythmogenic cardiomyopathy.

Heart Rhythm 2013 Mar 23;10(3):412-9. Epub 2012 Nov 23.

Department of Medical Physiology, University Medical Center Utrecht, Utrecht, The Netherlands.

Background: Arrhythmogenic cardiomyopathy (AC) is closely associated with desmosomal mutations in a majority of patients. Arrhythmogenesis in patients with AC is likely related to remodeling of cardiac gap junctions and increased levels of fibrosis. Recently, using experimental models, we also identified sodium channel dysfunction secondary to desmosomal dysfunction.

Objective: To assess the immunoreactive signal levels of the sodium channel protein NaV1.5, as well as connexin43 (Cx43) and plakoglobin (PKG), in myocardial specimens obtained from patients with AC.

Methods: Left and right ventricular free wall postmortem material was obtained from 5 patients with AC and 5 controls matched for age and sex. Right ventricular septal biopsies were taken from another 15 patients with AC. All patients fulfilled the 2010 revised Task Force Criteria for the diagnosis of AC. Immunohistochemical analyses were performed using antibodies against Cx43, PKG, NaV1.5, plakophilin-2, and N-cadherin.

Results: N-cadherin and desmoplakin immunoreactive signals and distribution were normal in patients with AC compared to controls. Plakophilin-2 signals were unaffected unless a plakophilin-2 mutation predicting haploinsufficiency was present. Distribution was unchanged compared to that in controls. Immunoreactive signal levels of PKG, Cx43, and NaV1.5 were disturbed in 74%, 70%, and 65% of the patients, respectively.

Conclusions: A reduced immunoreactive signal of PKG, Cx43, and NaV1.5 at the intercalated disks can be observed in a large majority of the patients. Decreased levels of Nav1.5 might contribute to arrhythmia vulnerability and, in the future, potentially could serve as a new clinically relevant tool for risk assessment strategies.
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http://dx.doi.org/10.1016/j.hrthm.2012.11.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3608196PMC
March 2013

Clinical and genetic characterization of patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy caused by a plakophilin-2 splice mutation.

Cardiology 2012 7;123(3):181-9. Epub 2012 Nov 7.

Department of Medical Genetics, University Medical Center Utrecht, University of Utrecht, The Netherlands.

Objectives: Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is characterized by fibrofatty replacement of cardiomyocytes. In around 50% of index patients, a genetic predisposition is demonstrated. The purpose of this study was to examine a plakophilin-2 (PKP2) splice site mutation, c.2489+4A>C, identified in 4 separately ascertained Dutch ARVD/C families.

Methods: Genealogical studies and comprehensive screening of 5 desmosomal genes were undertaken. Reverse transcriptase PCR (RT-PCR) and subsequent sequencing was performed.

Results: An A-to-C change (c.2489+4A>C) near the splice donor site of intervening sequence 12 of PKP2 was found in all 4 families. Based on pedigree data and haplotype sharing, a common ancestor should be situated more than 7 generations ago. RT-PCR demonstrated the presence of aberrant messenger RNA. Clinical manifestations ranged from severe disease to nonpenetrance in elderly mutation carriers.

Conclusions: This founder mutation in PKP2 is predicted to lead to the presence of a dysfunctional PKP2 protein, whereas most truncating mutations are expected to lead to loss of protein. Mutation carriers displayed a wide range of disease severity, suggesting that PKP2 mutations alone are not sufficient to cause disease, which results in the variable expression and incomplete penetrance characteristic of ARVD/C mutations.
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http://dx.doi.org/10.1159/000342717DOI Listing
May 2013