Publications

  • [Show abstract] [Hide abstract]
    ABSTRACT: Two proα1(IV) chains, encoded by COL4A1, form trimers that contain, in addition, a proα2(IV) chain encoded by COL4A2 and are the major component of the basement membrane in many tissues. Since 2005, COL4A1 mutations have been known as an autosomal dominant cause of hereditary porencephaly. COL4A1 and COL4A2 mutations have been reported with a broader spectrum of cerebrovascular, renal, ophthalmological, cardiac, and muscular abnormalities, indicated as "COL4A1 mutation-related disorders." Genetic counseling is challenging because of broad phenotypic variation and reduced penetrance. At the Erasmus University Medical Center, diagnostic DNA analysis of both COL4A1 and COL4A2 in 183 index patients was performed between 2005 and 2013. In total, 21 COL4A1 and 3 COL4A2 mutations were identified, mostly in children with porencephaly or other patterns of parenchymal hemorrhage, with a high de novo mutation rate of 40% (10/24). The observations in 13 novel families harboring either COL4A1 or COL4A2 mutations prompted us to review the clinical spectrum. We observed recognizable phenotypic patterns and propose a screening protocol at diagnosis. Our data underscore the importance of COL4A1 and COL4A2 mutations in cerebrovascular disease, also in sporadic patients. Follow-up data on symptomatic and asymptomatic mutation carriers are needed for prognosis and appropriate surveillance.Genet Med advance online publication 26 February 2015Genetics in Medicine (2015); doi:10.1038/gim.2014.210.
    Genetics in medicine: official journal of the American College of Medical Genetics 02/2015; DOI:10.1038/gim.2014.210 · 6.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by mutations in TSC1 and TSC2. Conventional DNA diagnostic screens identify a TSC1 or TSC2 mutation in 75 - 90% of individuals categorised with definite TSC. The remaining individuals either have a mutation that is undetectable using conventional methods, or possibly a mutation in another as yet unidentified gene. Here we apply a targeted Next Generation Sequencing (NGS) approach to screen the complete TSC1 and TSC2 genomic loci in 7 individuals fulfilling the clinical diagnostic criteria for definite TSC in whom no TSC1 or TSC2 mutations were identified using conventional screening methods. We identified and confirmed pathogenic mutations in 3 individuals. In the remaining individuals we identified variants of uncertain clinical significance. The identified variants included mosaic changes, changes located deep in intronic sequences and changes affecting promoter regions that would not have been identified using exon-only based analyses. Targeted NGS of the TSC1 and TSC2 loci is a suitable method to increase the yield of mutations identified in the TSC patient population.
    BMC Medical Genetics 02/2015; 16(1):10. DOI:10.1186/s12881-015-0155-4 · 2.45 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Identification of pathogenic variants in monogenic diseases is an important aspect of diagnosis, genetic counseling, and prediction of disease severity. Pathogenic mechanisms involved include changes in gene expression, RNA processing, and protein translation. Variants affecting pre-mRNA splicing are difficult to predict due to the complex mechanism of splicing regulation. A generic approach to systematically detect and characterize effects of sequence variants on splicing would improve current diagnostic practice. Here, it is shown that such approach is feasible by combining flanking exon RT-PCR, sequence analysis of PCR products, and exon-internal quantitative RT-PCR for all coding exons. Application of this approach to one novel and six previously published variants in the acid-alpha glucosidase (GAA) gene causing Pompe disease enabled detection of a total of eleven novel splicing events. Aberrant splicing included cryptic splice site usage, intron retention, and exon skipping. Importantly, the extent of leaky wild type splicing correlated with disease onset and severity. These results indicate that this approach enables sensitive detection and in-depth characterization of variants affecting splicing, many of which are still unrecognized or poorly understood. The approach is generic and should be adaptable for application to other monogenic diseases to aid in improved diagnostics.This article is protected by copyright. All rights reserved
    Human Mutation 01/2015; 36(1). DOI:10.1002/humu.22705 · 5.05 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The TSC1-TSC2-TBC1D7 complex is an important negative regulator of the mechanistic target of rapamycin complex 1 that controls cell growth in response to environmental cues. Inactivating TSC1 and TSC2 mutations cause tuberous sclerosis complex (TSC), an autosomal dominant disorder characterised by the occurrence of benign tumours in various organs and tissues, notably the brain, skin and kidneys. TBC1D7 mutations have not been reported in TSC patients but homozygous inactivation of TBC1D7 causes megaencephaly and intellectual disability. Here, using an exon-specific deletion strategy, we demonstrate that some regions of TSC1 are not necessary for the core function of the TSC1-TSC2 complex. Furthermore, we show that the TBC1D7 binding site is encoded by TSC1 exon 22 and identify amino acid residues involved in the TSC1-TBC1D7 interaction.
    PLoS ONE 04/2014; 9(4):e93940. DOI:10.1371/journal.pone.0093940 · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: So far only mutations in the filamin A gene (FLNA) have been identified as causing familial mitral valve prolapse (MVP). Previous studies have linked dysregulation of the transforming growth factor beta (TGF-β) cytokine family to MVP. We investigated whether mutations in the TGF-β receptors genes type I (TGFBR1) and II (TGFBR2) underlie isolated familial MVP cases. Eight families with isolated familial MVP were evaluated clinically and genetically. Ventricular arrhythmias were present in five of the eight families and sudden cardiac death occurred in six patients. Tissue obtained during mitral valve surgery or autopsy was available for histological examination in six cases; all demonstrated myxomatous degeneration. A previously described FLNA missense mutation (p.G288R) was identified in one large family, but no mutations were discovered in TGFBR1 or TGFBR2. An FLNA missense mutation was identified in one family but we found no TGFBR1 or TGFBR2 mutations. Our results suggest that TGFBR1 and TGFBR2 mutations do not play a major role in isolated myxomatous valve dystrophy. Screening for FLNA mutations is recommended in familial myxomatous valvular dystrophy, particularly if X-linked inheritance is suspected. © 2013 Wiley Periodicals, Inc.
    American Journal of Medical Genetics Part A 01/2014; 164(1). DOI:10.1002/ajmg.a.36211 · 2.05 Impact Factor
  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mutations in FLNA (Filamin A, OMIM 300017) cause X-linked periventricular nodular heterotopia (XL-PNH). XL-PNH-associated mutations are considered lethal in hemizygous males. However, a few males with unusual mutations (including distal truncating and hypomorphic missense mutations), and somatic mosaicism have been reported to survive past infancy. Two brothers had an atypical presentation with failure to thrive and distinct facial appearance including hypertelorism. Evaluations of these brothers and their affected cousin showed systemic involvement including severe intestinal malfunction, malrotation, congenital short bowel, PNH, pyloric stenosis, wandering spleen, patent ductus arteriosus, atrial septal defect, inguinal hernia, and vesicoureteral reflux. The unanticipated finding of PNH led to FLNA testing and subsequent identification of a novel no-stop FLNA mutation (c.7941_7942delCT, p.(*2648Serext*100)). Western blotting and qRT-PCR of patients' fibroblasts showed diminished levels of protein and mRNA. This FLNA mutation, the most distal reported so far, causes in females classical XL-PNH, but in males an unusual, multi-organ phenotype, providing a unique insight into the FLNA-associated phenotypes. © 2013 Wiley Periodicals, Inc.
    American Journal of Medical Genetics Part A 09/2013; 161(9). DOI:10.1002/ajmg.a.36109 · 2.05 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: BACKGROUND: The BIG2 protein, coded by ARFGEF2 indirectly assists neuronal proliferation and migration during cortical development. Mutations in ARFGEF2 have been reported as a rare cause of periventricular heterotopia. METHODS: The presence of periventricular heterotopia, acquired microcephaly and suspected recessive inheritance led to mutation analysis of ARFGEF2 in two affected siblings and their healthy consanguineous parents, after mutations in FLNA had been ruled out. RESULTS: A homozygous c.242_249delins7 (p.Pro81fs) mutation in exon 3 of ARFGEF2 was identified in the siblings. The alteration is a combination of 2 missense mutations (c.242C > A and c.247G > T) and a frameshift mutation (c.249delA) resulting in a premature stop codon. The clinical phenotype was characterized by dystonic quadriplegia, marked developmental delay, obstructive cardiomyopathy, recurrent infections and feeding difficulties. Degenerative features included early regression, acquired microcephaly and cerebral atrophy. Brain MRI revealed bilateral periventricular heterotopia, small corpus callosum, cerebral and hippocampal atrophy and hyperintensity in the putamen. CONCLUSION: Mutations in ARFGEF2 can be anticipated based on characteristic clinical and imaging features.
    European journal of paediatric neurology: EJPN: official journal of the European Paediatric Neurology Society 06/2013; 17(6). DOI:10.1016/j.ejpn.2013.05.002 · 1.93 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: NF1 mutations are the underlying cause of Neurofibromatosis type 1 (NF1), a neuro-cardio-facio-cutaneous syndrome (NCFC). Because of the clinical overlap between NCFCs, genetic analysis of NF1 is necessary to confirm a clinical diagnosis NF1. The present report describes the clinical and genetic findings of 18 years of NF1 molecular diagnostics in the Netherlands. A pathogenic mutation was found in 59.3% (1178/1985) of the index patients, mostly de novo (73.8%). The majority of the index patients (64.3%) fulfilled the NIH NF1 criteria, a pathogenic mutation was found in 80.9% of these patients. Seventy-four percent of the index patients with an NF1 pathogenic mutation and not fulfilling the NF1 criteria is <12yr, in agreement with the fact that some NF1 symptoms appear after puberty. Genotype-phenotype correlations were studied for 527 index patients. NF1 patients with a type 1 microdeletion have a 6-fold higher risk of special education versus NF1 patients with an intragenic mutation. No evidently milder NF1 phenotype for patients with a missense mutation was observed. Forty-six prenatal analyses were performed in 28 (2.4%) families, of which 29 (63%) showed heterozygosity for the familial pathogenic mutation. This indicates that there is a need for prenatal NF1 testing.
    Clinical Genetics 05/2013; DOI:10.1111/cge.12187 · 3.65 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background Mucopolysaccharidosis type VI (Maroteaux-Lamy syndrome; MPS VI) is an autosomal recessive lysosomal storage disorder in which deficiency of N-acetylgalactosamine 4-sulfatase (arylsulfatase B; ARSB) leads to the storage of glycosaminoglycans (GAGs) in connective tissue. The genotype-phenotype correlation has been addressed in several publications but the picture is not complete. Since 2007, enzyme-replacement therapy (ERT) has been available for patients with MPS VI in the Netherlands. The purpose of our study was to learn more about the genotype-phenotype correlations in MPS VI and the antibody response to ERT with galsulfase (recombinant human arylsulfatase B). Methods We identified ARSB mutations in 12 patients and used site-directed mutagenesis to study their effect. Antibody levels to galsulfase were measured using ELISA and a semi-quantitative immunoprecipitation method. We assessed the in vitro inhibitory effect of antibodies on galsulfase uptake and their effect on clinical outcome. Results Five patients had a rapidly progressive phenotype and seven a slowly progressive phenotype. In total 9 pathogenic mutations were identified including 4 novel mutations (N301K, V332G, A237D, and c.1142 + 2 T > C) together composing 8 pathogenic genotypes. Most mutations appeared not to affect the synthesis of ARSB (66 kD precursor), but to hamper its maturation (43 kD ARSB). Disease severity was correlated with urinary GAG excretion. All patients developed antibodies to galsulfase within 26 weeks of treatment. It was demonstrated that these antibodies can inhibit the uptake of galsulfase in vitro. Conclusions The clinical phenotypes and the observed defects in the biosynthesis of ARSB show that some of the mutations that we identified are clearly more severe than others. Patients receiving galsulfase as enzyme-replacement therapy can develop antibodies towards the therapeutic protein. Though most titers are modest, they can exceed a level at which they potentially affect the clinical outcome of enzyme-replacement therapy.
    Orphanet Journal of Rare Diseases 04/2013; 8(1):51. DOI:10.1186/1750-1172-8-51 · 3.96 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by mutations in the TSC1 or TSC2 genes. The TSC1 and TSC2 gene products, TSC1 and TSC2, form a complex that inhibits the mammalian target of rapamycin (mTOR) complex 1 (TORC1). Here, we investigate the effects of 78 TSC2 variants identified in individuals suspected of TSC, on the function of the TSC1-TSC2 complex. According to our functional assessment, 40 variants disrupted the TSC1-TSC2-dependent inhibition of TORC1. We classified 34 of these as pathogenic, three as probably pathogenic and three as possibly pathogenic. In one case, a likely effect on splicing as well as an effect on function was noted. In 15 cases, our functional assessment did not agree with the predictions of the SIFT amino acid substitution analysis software. Our data support the notion that different, nonterminating TSC2 mutations can have distinct effects on TSC1-TSC2 function, and therefore, on TSC pathology.
    Human Mutation 01/2013; 34(1). DOI:10.1002/humu.22202 · 5.05 Impact Factor
  • Human Mutation 01/2013; 34(2). DOI:10.1002/humu.22256 · 5.05 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background Mutations to the TSC1 and TSC2 genes cause the disease tuberous sclerosis complex. The TSC1 and TSC2 gene products form a protein complex that integrates multiple metabolic signals to regulate the activity of the target of rapamycin (TOR) complex 1 (TORC1) and thereby control cell growth. Here we investigate the quaternary structure of the TSC1-TSC2 complex by gel filtration and coimmunoprecipitation. Results TSC1 and TSC2 co-eluted in high molecular weight fractions by gel filtration. Coimmunoprecipitation of distinct tagged TSC1 and TSC2 isoforms demonstrated that TSC1-TSC2 complexes contain multiple TSC1 and TSC2 subunits. Conclusions TSC1 and TSC2 interact to form large complexes containing multiple TSC1 and TSC2 subunits.
    BMC Biochemistry 09/2012; 13(1). DOI:10.1186/1471-2091-13-18 · 1.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Pompe disease is an autosomal recessive lysosomal glycogen storage disorder, characterized by progressive muscle weakness. Deficiency of acid α-glucosidase (EC; 3.2.1.20/3) can be caused by numerous pathogenic variants in the GAA gene. The Pompe Disease Mutation Database at http://www.pompecenter.nl aims to list all variants and their effect. This update reports on 94 variants. We examined 35 novel and 34 known mutations by site-directed mutagenesis and transient expression in COS-7 cells or HEK293T cells. Each of these mutations was given a severity rating using a previously published system, based on the level of acid α-glucosidase activity in medium and transfected cells and on the quantity and quality of the different molecular mass species in the posttranslational modification and transport of acid α-glucosidase. This approach enabled to classify 55 missense mutations as pathogenic and 13 as likely nonpathogenic. Based on their nature and the use of in silico analysis (Alamut® software), 12 of the additional 25 novel mutations were predicted to be pathogenic including 4 splicing mutations, 6 mutations leading to frameshift, and 2 point mutations causing stop codons. Seven of the additional mutations were considered nonpathogenic (4 silent and 3 occurring in intron regions), and 6 are still under investigation. Hum Mutat 33:1161–1165, 2012. © 2012 Wiley Periodicals, Inc.
    Human Mutation 08/2012; 33(8):1161-1165. DOI:10.1002/humu.22108 · 5.05 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Aims: Most patients (98%) with Friedreich's ataxia (FRDA) are homozygous for the GAA repeat expansion in FXN. Only a few compound heterozygous patients with an expanded repeat on one allele and a point mutation or an intragenic FXN deletion on the other allele are described. In a minority of the patients only a heterozygous pattern of the repeat expansion can be detected. Using array analysis after GAA repeat expansion testing, we identified a FRDA patient who is compound heterozygous for an expanded GAA repeat and a complete FXN deletion. Since not only repeat expansions and point mutations, but also large rearrangements can be the underlying cause of FRDA, a quantitative test should also be performed in case a patient shows only one allele with an expanded GAA repeat in FXN.
    Genetic Testing and Molecular Biomarkers 06/2012; 16(9):1015-8. DOI:10.1089/gtmb.2012.0012 · 1.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Pompe disease is an autosomal recessive lysosomal glycogen storage disorder, characterized by progressive muscle weakness. Deficiency of acid α-glucosidase (EC; 3.2.1.20/3) can be caused by numerous pathogenic variants in the GAA gene. The Pompe Disease Mutation Database at http://www.pompecenter.nl aims to list all variants and their effect. This update reports on 94 variants. We examined 35 novel and 34 known mutations by site-directed mutagenesis and transient expression in COS-7 cells or HEK293T cells. Each of these mutations was given a severity rating using a previously published system, based on the level of acid α-glucosidase activity in medium and transfected cells and on the quantity and quality of the different molecular mass species in the posttranslational modification and transport of acid α-glucosidase. This approach enabled to classify 55 missense mutations as pathogenic and 13 as likely nonpathogenic. Based on their nature and the use of in silico analysis (Alamut® software), 12 of the additional 25 novel mutations were predicted to be pathogenic including 4 splicing mutations, 6 mutations leading to frameshift, and 2 point mutations causing stop codons. Seven of the additional mutations were considered nonpathogenic (4 silent and 3 occurring in intron regions), and 6 are still under investigation.
    Human Mutation 05/2012; 33(8):1161-5. · 5.05 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Mutations in the ARX gene, at Xp22.3, cause several disorders, including infantile spasms, X-linked lissencephaly with abnormal genitalia (XLAG), callosal agenesis and isolated intellectual disability. Genotype/phenotype studies suggested that polyalanine tract expansion is associated with non-malformative phenotypes, while missense and nonsense mutations cause cerebral malformations, however, patients with structural normal brain and missense mutations have been reported. We report on a male patient born with cleft lip and palate who presented with infantile spasms and hemiplegia. MRI showed agenesis of corpus callosum (ACC), an interhemispheric cyst, periventricular nodular heterotopia (PVNH), and extensive left frontal polymicrogyria (PMG). Sequencing of the ARX gene in the patient identified a six basepair insertion (c.335ins6, exon 2). The insertion leads to a two-residue expansion of the first polyalanine tract and was described previously in a family with non-syndromic X-linked mental retardation. To our knowledge, ARX mutation causing PMG and PVNH is unique, but the spasms and ACC are common in ARX mutations. Clinicians should be aware of the broad clinical range of ARX mutations, and further studies are necessary to investigate the association with PMG and PVNH and to identify possible modifying factors.
    American Journal of Medical Genetics Part A 05/2012; 158A(6):1472-6. DOI:10.1002/ajmg.a.35365 · 2.05 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Het klinisch beeld van erfelijke metabole ziekten (EMZ) is zeer variabel, van bijzonder mild tot niet-verenigbaar met het leven. Deze klinische heterogeniteit in combinatie met de zeldzaamheid van individuele EMZ kan het stellen van een diagnose bemoeilijken. Recente ontwikkelingen in zowel de diagnostiek als de behandeling van EMZ hebben de prognose voor patiënten met EMZ aanzienlijk verbeterd en maken het essentieel dat er voldoende kennis van deze aandoeningen is bij (kinder)artsen. Om tot een snelle en nauwkeurige diagnose van EMZ te komen, is gespecialiseerde diagnostiek vereist naar (1) metabolietconcentraties in bloed en urine, (2) enzymactiviteit(en) in bloedcellen, gekweekte huidfibroblasten of weefselbiopten, en (3) genmutaties. Dit artikel beschrijft een aantal kanten van deze drie niveaus van laboratoriumdiagnostiek van EMZ, waaronder mogelijkheden en beperkingen, maar ook praktische aspecten zoals in te zenden monsters. Vanwege de complexiteit van genetische metabole aandoeningen willen wij in dit artikel onderstrepen dat overleg tussen aanvrager en laboratorium enerzijds en laboratoria onderling anderzijds van groot belang is. Dit geldt in het bijzonder voor de lysosomale stapelingsziekten, waarvoor gericht inzetten van diagnostiek een voorwaarde is om tot de juiste diagnose te komen.
    Tijdschrift voor kindergeneeskunde 04/2012; 2010(2):49-56. DOI:10.1007/s12456-010-0016-1
  • [Show abstract] [Hide abstract]
    ABSTRACT: Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by mutations in the TSC1 or TSC2 genes. The TSC1 and TSC2 gene products, TSC1 and TSC2, form a complex that inhibits the mammalian target of rapamycin (mTOR) complex 1 (TORC1). Previously, we demonstrated that pathogenic amino acid substitutions in the N-terminal domain of TSC1 (amino acids 50-224) are destabilizing. Here we investigate an additional 21 unclassified TSC1 variants. Our functional assessment identified four substitutions (p.L61R, p.G132D, p.F158S, and p.R204P) between amino acids 50 and 224 that reduced TSC1 stability and prevented the TSC1-TSC2-dependent inhibition of TORC1. In four cases (20%), our functional assessment did not agree with the predictions of the SIFT amino acid substitution analysis software. Our new data confirm our previous finding that the N-terminal region of TSC1 is essential for TSC1 function.
    Human Mutation 03/2012; 33(3):476-9. DOI:10.1002/humu.22007 · 5.05 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Familial porencephaly, leukoencephalopathy and small-vessel disease belong to the spectrum of disorders ascribed to dominant mutations in the gene encoding for type IV collagen alpha-1 (COL4A1). Mice harbouring mutations in either Col4a1 or Col4a2 suffer from porencephaly, hydrocephalus, cerebral and ocular bleeding and developmental defects. We observed porencephaly and white matter lesions in members from two families that lack COL4A1 mutations. We hypothesized that COL4A2 mutations confer genetic predisposition to porencephaly, therefore we sequenced COL4A2 in the family members and characterized clinical, neuroradiological and biochemical phenotypes. Genomic sequencing of COL4A2 identified the heterozygous missense G1389R in exon 44 in one family and the c.3206delC change in exon 34 leading to frame shift and premature stop, in the second family. Fragmentation and duplication of epidermal basement membranes were observed by electron microscopy in a c.3206delC patient skin biopsy, consistent with abnormal collagen IV network. Collagen chain accumulation and endoplasmic reticulum (ER) stress have been proposed as cellular mechanism in COL4A1 mutations. In COL4A2 (3206delC) fibroblasts we detected increased rates of apoptosis and no signs of ER stress. Mutation phenotypes varied, including porencephaly, white matter lesions, cerebellar and optic nerve hypoplasia and unruptured carotid aneurysm. In the second family however, we found evidence for additional factors contributing to the phenotype. We conclude that dominant COL4A2 mutations are a novel major risk factor for familial cerebrovascular disease, including porencephaly and small-vessel disease with reduced penetrance and variable phenotype, which might also be modified by other contributing factors.
    European journal of human genetics: EJHG 02/2012; 20(8):844-51. DOI:10.1038/ejhg.2012.20 · 4.23 Impact Factor

29 Following View all

87 Followers View all