Publications by authors named "Astrid S Plomp"

28 Publications

  • Page 1 of 1

Variants in the SK2 channel gene (KCNN2) lead to dominant neurodevelopmental movement disorders.

Brain 2020 12;143(12):3564-3573

Institut du Cerveau et de la Moelle épinière (ICM), Sorbonne Université, UMR S 1127, Inserm U1127, CNRS UMR 7225, F-75013 Paris, France.

KCNN2 encodes the small conductance calcium-activated potassium channel 2 (SK2). Rodent models with spontaneous Kcnn2 mutations show abnormal gait and locomotor activity, tremor and memory deficits, but human disorders related to KCNN2 variants are largely unknown. Using exome sequencing, we identified a de novo KCNN2 frameshift deletion in a patient with learning disabilities, cerebellar ataxia and white matter abnormalities on brain MRI. This discovery prompted us to collect data from nine additional patients with de novo KCNN2 variants (one nonsense, one splice site, six missense variants and one in-frame deletion) and one family with a missense variant inherited from the affected mother. We investigated the functional impact of six selected variants on SK2 channel function using the patch-clamp technique. All variants tested but one, which was reclassified to uncertain significance, led to a loss-of-function of SK2 channels. Patients with KCNN2 variants had motor and language developmental delay, intellectual disability often associated with early-onset movement disorders comprising cerebellar ataxia and/or extrapyramidal symptoms. Altogether, our findings provide evidence that heterozygous variants, likely causing a haploinsufficiency of the KCNN2 gene, lead to novel autosomal dominant neurodevelopmental movement disorders mirroring phenotypes previously described in rodents.
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http://dx.doi.org/10.1093/brain/awaa346DOI Listing
December 2020

Pathogenic effect of a TGFBR1 mutation in a family with Loeys-Dietz syndrome.

Mol Genet Genomic Med 2019 10 1;7(10):e00943. Epub 2019 Sep 1.

Department of Clinical Genetics, Amsterdam University Medical Centre, VUMC, Amsterdam Cardiovascular Sciences, Amsterdam, The Netherlands.

Background: Thoracic aortic aneurysms and dissections (TAAD) may have a heritable cause in up to 20% of cases. We aimed to investigate the pathogenic effect of a TGFBR1 mutation in relation to TAAD.

Methods: Co-segregation analysis was performed followed by functional investigations, including myogenic transdifferentiation.

Results: The c.1043G>A TGFBR1 mutation was found in the index patient, in a deceased brother, and in five presymptomatic family members. Evidence for pathogenicity was found by the predicted damaging effect of this mutation and the co-segregation in the family. Functional analysis with myogenic transdifferentiation of dermal fibroblasts to smooth muscle-like cells, revealed increased myogenic differentiation in patient cells with the TGFBR1 mutation, shown by a higher expression of myogenic markers ACTA2, MYH11 and CNN1 compared to cells from healthy controls.

Conclusion: Our findings confirm the pathogenic effect of the TGFBR1 mutation in causing TAAD in Loeys-Dietz syndrome and show increased myogenic differentiation of patient fibroblasts.
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http://dx.doi.org/10.1002/mgg3.943DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6785444PMC
October 2019

Biallelic loss-of-function P4HTM gene variants cause hypotonia, hypoventilation, intellectual disability, dysautonomia, epilepsy, and eye abnormalities (HIDEA syndrome).

Genet Med 2019 10 3;21(10):2355-2363. Epub 2019 Apr 3.

PEDEGO Research Unit and Medical Research Centre Oulu, University of Oulu and Oulu University Hospital, Oulu, Finland.

Purpose: A new syndrome with hypotonia, intellectual disability, and eye abnormalities (HIDEA) was previously described in a large consanguineous family. Linkage analysis identified the recessive disease locus, and genome sequencing yielded three candidate genes with potentially pathogenic biallelic variants: transketolase (TKT), transmembrane prolyl 4-hydroxylase (P4HTM), and ubiquitin specific peptidase 4 (USP4). However, the causative gene remained elusive.

Methods: International collaboration and exome sequencing were used to identify new patients with HIDEA and biallelic, potentially pathogenic, P4HTM variants. Segregation analysis was performed using Sanger sequencing. P4H-TM wild-type and variant constructs without the transmembrane region were overexpressed in insect cells and analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western blot.

Results: Five different homozygous or compound heterozygous pathogenic P4HTM gene variants were identified in six new and six previously published patients presenting with HIDEA. Hypoventilation, obstructive and central sleep apnea, and dysautonomia were identified as novel features associated with the phenotype. Characterization of three of the P4H-TM variants demonstrated yielding insoluble protein products and, thus, loss-of-function.

Conclusions: Biallelic loss-of-function P4HTM variants were shown to cause HIDEA syndrome. Our findings enable diagnosis of the condition, and highlight the importance of assessing the need for noninvasive ventilatory support in patients.
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http://dx.doi.org/10.1038/s41436-019-0503-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6774999PMC
October 2019

Macular Dystrophy and Cone-Rod Dystrophy Caused by Mutations in the RP1 Gene: Extending the RP1 Disease Spectrum.

Invest Ophthalmol Vis Sci 2019 03;60(4):1192-1203

Department of Advanced Ophthalmic Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan.

Purpose: To describe the clinical and genetic spectrum of RP1-associated retinal dystrophies.

Methods: In this multicenter case series, we included 22 patients with RP1-associated retinal dystrophies from 19 families from The Netherlands and Japan. Data on clinical characteristics, visual acuity, visual field, ERG, and retinal imaging were extracted from medical records over a mean follow-up of 8.1 years.

Results: Eleven patients were diagnosed with autosomal recessive macular dystrophy (arMD) or autosomal recessive cone-rod dystrophy (arCRD), five with autosomal recessive retinitis pigmentosa (arRP), and six with autosomal dominant RP (adRP). The mean age of onset was 40.3 years (range 14-56) in the patients with arMD/arCRD, 26.2 years (range 18-40) in adRP, and 8.8 years (range 5-12) in arRP patients. All patients with arMD/arCRD carried either the hypomorphic p.Arg1933* variant positioned close to the C-terminus (8 of 11 patients) or a missense variant in exon 2 (3 of 11 patients), compound heterozygous with a likely deleterious frameshift or nonsense mutation, or the p.Gln1916* variant. In contrast, all mutations identified in adRP and arRP patients were frameshift and/or nonsense variants located far from the C-terminus.

Conclusions: Mutations in the RP1 gene are associated with a broad spectrum of progressive retinal dystrophies. In addition to adRP and arRP, our study provides further evidence that arCRD and arMD are RP1-associated phenotypes as well. The macular involvement in patients with the hypomorphic RP1 variant suggests that macular function may remain compromised if expression levels of RP1 do not reach adequate levels after gene augmentation therapy.
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http://dx.doi.org/10.1167/iovs.18-26084DOI Listing
March 2019

Ocular albinism with infertility and late-onset sensorineural hearing loss.

Am J Med Genet A 2018 07;176(7):1587-1593

Department of Clinical Genetics, Aalborg University Hospital, Aalborg, Denmark.

Ocular albinism type 1 (OA1) is caused by mutations in the GPR143 gene located at Xp22.2. The manifestations, which are due to hypopigmentation, are confined to the eyes and optic pathway. OA1 associated with late-onset sensorineural hearing loss was previously reported in a single family and hypothesized to be caused by a contiguous gene deletion syndrome involving GPR143 and the adjacent gene, TBL1X. Here, we report on a family with OA1, infertility, late-onset sensorineural hearing loss, and a small interstitial Xp microdeletion including the GPR143, TBL1X, and SHROOM2 genes. In addition, we re-examined a patient previously described with OA1, infertility and a similar Xp deletion with audiologic follow-up showing a late-onset sensorineural hearing loss. Our results raise an intriguing question about the possibility for TBL1X (absence) involvement in this type of hearing loss. However, our study cannot claim a causative relationship and more convincing evidence is needed before the hypothesis can be accepted that TBL1X could be involved in late-onset sensorineural hearing loss and that ocular albinism with late-onset sensorineural hearing loss can present itself as a contiguous gene deletion/microdeletion syndrome. The finding of infertility in all affected male patients demonstrates that this deletion, including the SHROOM2 gene, may be a potentially causative X-linked genetic factor of male infertility.
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http://dx.doi.org/10.1002/ajmg.a.38836DOI Listing
July 2018

The Common ABCA4 Variant p.Asn1868Ile Shows Nonpenetrance and Variable Expression of Stargardt Disease When Present in trans With Severe Variants.

Invest Ophthalmol Vis Sci 2018 07;59(8):3220-3231

Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands.

Purpose: To assess the occurrence and the disease expression of the common p.Asn1868Ile variant in patients with Stargardt disease (STGD1) harboring known, monoallelic causal ABCA4 variants.

Methods: The coding and noncoding regions of ABCA4 were sequenced in 67 and 63 STGD1 probands respectively, harboring monoallelic ABCA4 variants. In case p.Asn1868Ile was detected, segregation analysis was performed whenever possible. Probands and affected siblings harboring p.Asn1868Ile without additional variants in cis were clinically evaluated retrospectively. Two asymptomatic siblings carrying the same ABCA4 variants as their probands were clinically examined. The penetrance of p.Asn1868Ile was calculated using allele frequency data of ABCA4 variants in non-Finnish European individuals.

Results: The p.Asn1868Ile variant was found in cis with known variants in 14/67 probands. In 27/67 probands, we identified p.Asn1868Ile without additional variants in cis, in combination with known, mainly severe ABCA4 variants. In 23/27 probands, the trans configuration was established. Among 27 probands and 6/7 STGD1 siblings carrying p.Asn1868Ile, 42% manifested late-onset disease (>44 years). We additionally identified four asymptomatic relatives carrying a combination of a severe variant and p.Asn1868Ile; ophthalmologic examination in two persons did not reveal STGD1. Based on ABCA4 allele frequency data, we conservatively estimated the penetrance of p.Asn1868Ile, when present in trans with a severe variant, to be below 5%.

Conclusions: A significant fraction of genetically unexplained STGD1 cases carries p.Asn1868Ile as a second variant. Our findings suggest exceptional differences in disease expression or even nonpenetrance of this ABCA4 variant, pointing toward an important role for genetic or environmental modifiers in STGD1.
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http://dx.doi.org/10.1167/iovs.18-23881DOI Listing
July 2018

Further delineation of Malan syndrome.

Hum Mutat 2018 09 25;39(9):1226-1237. Epub 2018 Jun 25.

Department of Pediatrics, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.

Malan syndrome is an overgrowth disorder described in a limited number of individuals. We aim to delineate the entity by studying a large group of affected individuals. We gathered data on 45 affected individuals with a molecularly confirmed diagnosis through an international collaboration and compared data to the 35 previously reported individuals. Results indicate that height is > 2 SDS in infancy and childhood but in only half of affected adults. Cardinal facial characteristics include long, triangular face, macrocephaly, prominent forehead, everted lower lip, and prominent chin. Intellectual disability is universally present, behaviorally anxiety is characteristic. Malan syndrome is caused by deletions or point mutations of NFIX clustered mostly in exon 2. There is no genotype-phenotype correlation except for an increased risk for epilepsy with 19p13.2 microdeletions. Variants arose de novo, except in one family in which mother was mosaic. Variants causing Malan and Marshall-Smith syndrome can be discerned by differences in the site of stop codon formation. We conclude that Malan syndrome has a well recognizable phenotype that usually can be discerned easily from Marshall-Smith syndrome but rarely there is some overlap. Differentiation from Sotos and Weaver syndrome can be made by clinical evaluation only.
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http://dx.doi.org/10.1002/humu.23563DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6175110PMC
September 2018

Equivalent missense variant in the FOXP2 and FOXP1 transcription factors causes distinct neurodevelopmental disorders.

Hum Mutat 2017 11 14;38(11):1542-1554. Epub 2017 Aug 14.

Language and Genetics Department, Max Planck Institute for Psycholinguistics, Nijmegen, The Netherlands.

The closely related paralogues FOXP2 and FOXP1 encode transcription factors with shared functions in the development of many tissues, including the brain. However, while mutations in FOXP2 lead to a speech/language disorder characterized by childhood apraxia of speech (CAS), the clinical profile of FOXP1 variants includes a broader neurodevelopmental phenotype with global developmental delay, intellectual disability, and speech/language impairment. Using clinical whole-exome sequencing, we report an identical de novo missense FOXP1 variant identified in three unrelated patients. The variant, p.R514H, is located in the forkhead-box DNA-binding domain and is equivalent to the well-studied p.R553H FOXP2 variant that cosegregates with CAS in a large UK family. We present here for the first time a direct comparison of the molecular and clinical consequences of the same mutation affecting the equivalent residue in FOXP1 and FOXP2. Detailed functional characterization of the two variants in cell model systems revealed very similar molecular consequences, including aberrant subcellular localization, disruption of transcription factor activity, and deleterious effects on protein interactions. Nonetheless, clinical manifestations were broader and more severe in the three cases carrying the p.R514H FOXP1 variant than in individuals with the p.R553H variant related to CAS, highlighting divergent roles of FOXP2 and FOXP1 in neurodevelopment.
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http://dx.doi.org/10.1002/humu.23303DOI Listing
November 2017

A homozygous missense mutation in ERAL1, encoding a mitochondrial rRNA chaperone, causes Perrault syndrome.

Hum Mol Genet 2017 07;26(13):2541-2550

Department of Clinical Genetics, Academic Medical Center, 1105 AZ Amsterdam, The Netherlands.

Perrault syndrome (PS) is a rare recessive disorder characterized by ovarian dysgenesis and sensorineural deafness. It is clinically and genetically heterogeneous, and previously mutations have been described in different genes, mostly related to mitochondrial proteostasis. We diagnosed three unrelated females with PS and set out to identify the underlying genetic cause using exome sequencing. We excluded mutations in the known PS genes, but identified a single homozygous mutation in the ERAL1 gene (c.707A > T; p.Asn236Ile). Since ERAL1 protein binds to the mitochondrial 12S rRNA and is involved in the assembly of the small mitochondrial ribosomal subunit, the identified variant represented a likely candidate. In silico analysis of a 3D model for ERAL1 suggested that the mutated residue hinders protein-substrate interactions, potentially affecting its function. On a molecular basis, PS skin fibroblasts had reduced ERAL1 protein levels. Complexome profiling of the cells showed an overall decrease in the levels of assembled small ribosomal subunit, indicating that the ERAL1 variant affects mitochondrial ribosome assembly. Moreover, levels of the 12S rRNA were reduced in the patients, and were rescued by lentiviral expression of wild type ERAL1. At the physiological level, mitochondrial respiration was markedly decreased in PS fibroblasts, confirming disturbed mitochondrial function. Finally, knockdown of the C. elegans ERAL1 homologue E02H1.2 almost completely blocked egg production in worms, mimicking the compromised fertility in PS-affected women. Our cross-species data in patient cells and worms support the hypothesis that mutations in ERAL1 can cause PS and are associated with changes in mitochondrial metabolism.
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http://dx.doi.org/10.1093/hmg/ddx152DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5965403PMC
July 2017

Diagnostic exome sequencing in 266 Dutch patients with visual impairment.

Eur J Hum Genet 2017 05 22;25(5):591-599. Epub 2017 Feb 22.

Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands.

Inherited eye disorders have a large clinical and genetic heterogeneity, which makes genetic diagnosis cumbersome. An exome-sequencing approach was developed in which data analysis was divided into two steps: the vision gene panel and exome analysis. In the vision gene panel analysis, variants in genes known to cause inherited eye disorders were assessed for pathogenicity. If no causative variants were detected and when the patient consented, the entire exome data was analyzed. A total of 266 Dutch patients with different types of inherited eye disorders, including inherited retinal dystrophies, cataract, developmental eye disorders and optic atrophy, were investigated. In the vision gene panel analysis (likely), causative variants were detected in 49% and in the exome analysis in an additional 2% of the patients. The highest detection rate of (likely) causative variants was in patients with inherited retinal dystrophies, for instance a yield of 63% in patients with retinitis pigmentosa. In patients with developmental eye defects, cataract and optic atrophy, the detection rate was 50, 33 and 17%, respectively. An exome-sequencing approach enables a genetic diagnosis in patients with different types of inherited eye disorders using one test. The exome approach has the same detection rate as targeted panel sequencing tests, but offers a number of advantages. For instance, the vision gene panel can be frequently and easily updated with additional (novel) eye disorder genes. Determination of the genetic diagnosis improved the clinical diagnosis, regarding the assessment of the inheritance pattern as well as future disease perspective.
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http://dx.doi.org/10.1038/ejhg.2017.9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5437915PMC
May 2017

The diagnostic yield of whole-exome sequencing targeting a gene panel for hearing impairment in The Netherlands.

Eur J Hum Genet 2017 02 21;25(3):308-314. Epub 2016 Dec 21.

The Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands.

Hearing impairment (HI) is genetically heterogeneous which hampers genetic counseling and molecular diagnosis. Testing of several single HI-related genes is laborious and expensive. In this study, we evaluate the diagnostic utility of whole-exome sequencing (WES) targeting a panel of HI-related genes. Two hundred index patients, mostly of Dutch origin, with presumed hereditary HI underwent WES followed by targeted analysis of an HI gene panel of 120 genes. We found causative variants underlying the HI in 67 of 200 patients (33.5%). Eight of these patients have a large homozygous deletion involving STRC, OTOA or USH2A, which could only be identified by copy number variation detection. Variants of uncertain significance were found in 10 patients (5.0%). In the remaining 123 cases, no potentially causative variants were detected (61.5%). In our patient cohort, causative variants in GJB2, USH2A, MYO15A and STRC, and in MYO6 were the leading causes for autosomal recessive and dominant HI, respectively. Segregation analysis and functional analyses of variants of uncertain significance will probably further increase the diagnostic yield of WES.
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http://dx.doi.org/10.1038/ejhg.2016.182DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5315517PMC
February 2017

LONG-TERM FOLLOW-UP OF PATIENTS WITH RETINITIS PIGMENTOSA TYPE 12 CAUSED BY CRB1 MUTATIONS: A Severe Phenotype With Considerable Interindividual Variability.

Retina 2017 Jan;37(1):161-172

*Department of Clinical Genetics, Academic Medical Center, Amsterdam, the Netherlands; †The Rotterdam Eye Hospital, Rotterdam, the Netherlands; ‡Rivas Zorggroep, Vianen, the Netherlands; §Department of Genome Analysis, Academic Medical Center, Amsterdam, the Netherlands; ¶The Netherlands Institute for Neurosciences (NIN-KNAW), Amsterdam, the Netherlands; and **Department of Ophthalmology, Academic Medical Center, Amsterdam, the Netherlands.

Purpose: To examine the long-term clinical course and variability in a large pedigree segregating CRB1 type autosomal recessive retinitis pigmentosa.

Methods: An observational case study of 30 patients with CRB1 type autosomal recessive retinitis pigmentosa, homozygous for the CRB1 c.3122T > C; p.(Met1041Thr) mutation from a Dutch genetically isolated population in which the CRB1 gene was originally identified. The authors evaluated medical records, analyzed a questionnaire, and performed a comprehensive ophthalmic examination, including optical coherence tomography.

Results: Mean follow-up was 19 years (range 0-45 years, SD 15 years). With aging, patients showed progressive visual decline, deterioration of visual fields, increasing narrowing of the anterior chamber, increased prevalence of cataract, and an increase in the amount of intraretinal pigmentations. Fifty percent of patients had a visual acuity of ≤0.3 at Age 18 and of ≤0.1 at Age 35. Electroretinogram responses were severely reduced or absent already at a young age and optical coherence tomography showed increased retinal thickness with often cystoid maculopathy at young age, and thinning of the retina and disorientation of the photoreceptor layer in the late stages. The clinical course showed considerable interindividual variability, but intraindividual similarity between both eyes was the rule.

Conclusion: The wide and variable clinical spectrum in patients with the same CRB1 mutation supports the hypothesis that the CRB1 type autosomal recessive retinitis pigmentosa-phenotype is modulated by other factors. The clinical variability will make it harder to evaluate the effect of (upcoming) therapies for retinitis pigmentosa, although because of the intraindividual similarity between both eyes, the contralateral eye can be used as an excellent internal control.
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http://dx.doi.org/10.1097/IAE.0000000000001127DOI Listing
January 2017

De novo intrachromosomal gene conversion from OPN1MW to OPN1LW in the male germline results in Blue Cone Monochromacy.

Sci Rep 2016 06 24;6:28253. Epub 2016 Jun 24.

Institute for Ophthalmic Research, Centre for Ophthalmology, Tuebingen, Germany.

X-linked cone dysfunction disorders such as Blue Cone Monochromacy and X-linked Cone Dystrophy are characterized by complete loss (of) or reduced L- and M- cone function due to defects in the OPN1LW/OPN1MW gene cluster. Here we investigated 24 affected males from 16 families with either a structurally intact gene cluster or at least one intact single (hybrid) gene but harbouring rare combinations of common SNPs in exon 3 in single or multiple OPN1LW and OPN1MW gene copies. We assessed twelve different OPN1LW/MW exon 3 haplotypes by semi-quantitative minigene splicing assay. Nine haplotypes resulted in aberrant splicing of ≥20% of transcripts including the known pathogenic haplotypes (i.e. 'LIAVA', 'LVAVA') with absent or minute amounts of correctly spliced transcripts, respectively. De novo formation of the 'LIAVA' haplotype derived from an ancestral less deleterious 'LIAVS' haplotype was observed in one family with strikingly different phenotypes among affected family members. We could establish intrachromosomal gene conversion in the male germline as underlying mechanism. Gene conversion in the OPN1LW/OPN1MW genes has been postulated, however, we are first to demonstrate a de novo gene conversion within the lineage of a pedigree.
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http://dx.doi.org/10.1038/srep28253DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4919619PMC
June 2016

The RD5000 database: facilitating clinical, genetic, and therapeutic studies on inherited retinal diseases.

Invest Ophthalmol Vis Sci 2014 Nov 17;55(11):7355-60. Epub 2014 Nov 17.

Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands.

Inherited retinal diseases (IRDs) represent a clinical and genetic heterogeneous group of chorioretinal disorders. The frequency of persons affected by an IRD due to mutations in the same gene varies from 1 in 10,000 to less than 1 in a million. To perform meaningful genotype-phenotype analyses for rare genetic conditions, it is necessary to collect data from sizable populations. Although several standardized functional tests are used widely, ophthalmologic data usually are stored in local databases and not in multicenter databases that are linked with other centers. To be able to register ophthalmologic data of all Dutch patients with IRDs into one database, we developed the RD5000 database (RD5000db), which can harbor all ophthalmologic and selected genetic data. Authorization rights for the management, data entry, and data sharing have been set up, rendering this database into a user-friendly, secure, and widely used repository that will facilitate future studies into molecular genetics and therapies for IRDs. The RD5000db database has the potential to grow into a European standard for the registration of data from IRDs.
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http://dx.doi.org/10.1167/iovs.14-15317DOI Listing
November 2014

Twenty patients including 7 probands with autosomal dominant cutis laxa confirm clinical and molecular homogeneity.

Orphanet J Rare Dis 2013 Feb 25;8:36. Epub 2013 Feb 25.

Service de Dermatologie - Centre de référence national des Maladies Génétiques à Expression Cutanée MAGEC, INSERM U781, Hôpital Necker - Enfants Malades, Université Paris V-Descartes, 149, rue de Sèvres 75743 Paris Cedex 15, Paris, France.

Background: Elastin gene mutations have been associated with a variety of phenotypes. Autosomal dominant cutis laxa (ADCL) is a rare disorder that presents with lax skin, typical facial characteristics, inguinal hernias, aortic root dilatation and pulmonary emphysema. In most patients, frameshift mutations are found in the 3' region of the elastin gene (exons 30-34) which result in a C-terminally extended protein, though exceptions have been reported.

Methods: We clinically and molecularly characterized the thus far largest cohort of ADCL patients, consisting of 19 patients from six families and one sporadic patient.

Results: Molecular analysis showed C-terminal frameshift mutations in exon 30, 32, and 34 of the elastin gene and identified a mutational hotspot in exon 32 (c.2262delA). This cohort confirms the previously reported clinical constellation of skin laxity (100%), inguinal hernias (51%), aortic root dilatation (55%) and emphysema (37%).

Conclusion: ADCL is a clinically and molecularly homogeneous disorder, but intra- and interfamilial variability in the severity of organ involvement needs to be taken into account. Regular cardiovascular and pulmonary evaluations are imperative in the clinical follow-up of these patients.
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http://dx.doi.org/10.1186/1750-1172-8-36DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3599008PMC
February 2013

Mutation spectrum in RAB3GAP1, RAB3GAP2, and RAB18 and genotype-phenotype correlations in warburg micro syndrome and Martsolf syndrome.

Hum Mutat 2013 May;34(5):686-96

MRC Human Genetics Unit, Medical Research Council and Institute of Genetics and Molecular Medicine, University of Edinburgh, Scotland, UK.

Warburg Micro syndrome and Martsolf syndrome (MS) are heterogeneous autosomal-recessive developmental disorders characterized by brain, eye, and endocrine abnormalities. Causative biallelic germline mutations have been identified in RAB3GAP1, RAB3GAP2, or RAB18, each of which encode proteins involved in membrane trafficking. This report provides an up to date overview of all known disease variants identified in 29 previously published families and 52 new families. One-hundred and forty-four Micro and nine Martsolf families were investigated, identifying mutations in RAB3GAP1 in 41% of cases, mutations in RAB3GAP2 in 7% of cases, and mutations in RAB18 in 5% of cases. These are listed in Leiden Open source Variation Databases, which was created by us for all three genes. Genotype-phenotype correlations for these genes have now established that the clinical phenotypes in Micro syndrome and MS represent a phenotypic continuum related to the nature and severity of the mutations present in the disease genes, with more deleterious mutations causing Micro syndrome and milder mutations causing MS. RAB18 has not yet been linked to the RAB3 pathways, but mutations in all three genes cause an indistinguishable phenotype, making it likely that there is some overlap. There is considerable genetic heterogeneity for these disorders and further gene identification will help delineate these pathways.
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http://dx.doi.org/10.1002/humu.22296DOI Listing
May 2013

Complete COL1A1 allele deletions in osteogenesis imperfecta.

Genet Med 2010 Nov;12(11):736-41

Department of Clinical Genetics, VU University Medical Centre, Amsterdam, the Netherlands.

Purpose: To identify a molecular genetic cause in patients with a clinical diagnosis of osteogenesis imperfecta (OI) type I/IV.

Methods: The authors performed multiplex ligation-dependent probe amplification analysis of the COL1A1 gene in a group of 106 index patients.

Results: In four families with mild osteogenesis imperfecta and no other phenotypic abnormalities, a deletion of the complete COL1A1 gene on one allele was detected, a molecular finding that to our knowledge has not been described before, apart from a larger chromosomal deletion detected by fluorescent in situ hybridization encompassing the COL1A1 gene in a patient with mild osteogenesis imperfecta and other phenotypic abnormalities. Microarray analysis in three of the four families showed that it did not concern a founder mutation.

Conclusion: The clinical picture of complete COL1A1 allele deletions is a comparatively mild type of osteogenesis imperfecta. As such, multiplex ligation-dependent probe amplification analysis of the COL1A1 gene is a useful additional approach to defining the mutation in cases of suspected osteogenesis imperfecta type I with no detectable mutation.
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http://dx.doi.org/10.1097/GIM.0b013e3181f01617DOI Listing
November 2010

Dissecting the pathogenic mechanisms of mutations in the pore region of the human cone photoreceptor cyclic nucleotide-gated channel.

Hum Mutat 2010 Jul;31(7):830-9

Molecular Genetics Laboratory, Institute for Ophthalmic Research, Tuebingen, Germany.

The CNGA3 gene encodes the A3 subunit of the cone photoreceptor cyclic nucleotide-gated (CNG) channel, an essential component of the phototransduction cascade. Certain mutations in CNGA3 cause autosomal recessive achromatopsia, a retinal disorder characterized by severely reduced visual acuity, lack of color discrimination, photophobia, and nystagmus. We identified three novel mutations in the pore-forming region of CNGA3 (L363P, G367V, and E376K) in patients diagnosed with achromatopsia. We assessed the expression and function of channels with these three new and two previously described mutations (S341P and P372S) in a heterologous HEK293 cell expression system using Western blot, subcellular localization on the basis of immunocytochemistry, calcium imaging, and patch clamp recordings. In this first comparative functional analysis of disease-associated mutations in the pore of a CNG channel, we found impaired surface expression of S341P, L363P, and P372S mutants and reduced macroscopic currents for channels with the mutations S341P, G367V, and E376K. Calcium imaging and patch clamp experiments after incubation at 37 degrees C revealed nonfunctional homo- and heteromeric channels in all five mutants, but incubation at 27 degrees C combined with coexpression of the B3 subunit restored residual function of channels with the mutations S341P, G367V, and E376K.
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http://dx.doi.org/10.1002/humu.21283DOI Listing
July 2010

Proposal for updating the pseudoxanthoma elasticum classification system and a review of the clinical findings.

Am J Med Genet A 2010 Apr;152A(4):1049-58

Department of Clinical and Molecular Ophthalmogenetics, Netherlands Institute for Neuroscience, Amsterdam, the Netherlands.

Pseudoxanthoma elasticum (PXE) is a systemic disorder affecting elastic tissues most markedly in skin, retina, and blood vessels. It is caused by mutations in the ABCC6 gene and is transmitted in an autosomal recessive fashion. In 1994 a new classification system for PXE was published as the result of a consensus conference. Since then the ABCC6 gene has been discovered. We propose that there is a need for a classification system incorporating all relevant systemic symptoms and signs, based on standardized clinical, histological, and molecular biological examination techniques. We re-evaluated the histopathologic PXE signs and propose a classification system with unambiguous criteria leading to a consistent diagnosis of definitive, probable, or possible PXE world-wide. We put this proposed classification forward to encourage further debate on the diagnosis of this multi-organ disorder.
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http://dx.doi.org/10.1002/ajmg.a.33329DOI Listing
April 2010

Pseudoxanthoma elasticum: Wide phenotypic variation in homozygotes and no signs in heterozygotes for the c.3775delT mutation in ABCC6.

Genet Med 2009 Dec;11(12):852-8

Department of Clinical and Molecular Ophthalmogenetics, Netherlands Institute for Neuroscience, an Institute of the Royal Netherlands Academy of Arts and Sciences, Amsterdam.

Purpose: : Pseudoxanthoma elasticum is an autosomal recessive disorder of elastic tissue in the skin, eyes, and cardiovascular system, caused by mutations in the ABCC6 gene. The purpose of this study was to check variability in expression within one genotype and look for pseudoxanthoma elasticum signs in heterozygotes.

Methods: : We examined a relatively large, in comparison with the present literature, group of adult persons homozygous or heterozygous for the c.3775delT mutation in the ABCC6 gene, from a genetically isolated population in the Netherlands. All participants filled out a questionnaire and underwent standardized dermatologic and ophthalmologic examinations with photography of skin and fundus abnormalities. Skin biopsies from affected skin or a predilection site and/or a scar were examined and compared with biopsies from controls.

Results: : Skin abnormalities, ophthalmologic signs, and cardiovascular problems varied greatly among the 15 homozygous participants. There was no correlation among severity of skin, eyes, or cardiovascular abnormalities. None of the 44 heterozygous participants had any sign of pseudoxanthoma elasticum on dermatologic, histopathologic, and/or ophthalmologic examination, but 32% had cardiovascular disease.

Conclusion: : Individuals homozygous for the c.3775delT mutation can have a highly variable phenotype. We did not find pseudoxanthoma elasticum eye or skin abnormalities in the heterozygous family members.
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http://dx.doi.org/10.1097/GIM.0b013e3181c00a96DOI Listing
December 2009

ABCC6 mutations in pseudoxanthoma elasticum: an update including eight novel ones.

Mol Vis 2008 Jan 24;14:118-24. Epub 2008 Jan 24.

Department of Clinical and Molecular Ophthalmogenetics, Netherlands Institute for Neuroscience, an institute of the Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands.

Purpose: Pseudoxanthoma elasticum (PXE) is an autosomal recessive disorder of connective tissue, affecting the retina, the skin, and the cardiovascular system. PXE is caused by mutations in ABCC6. Up to now, the literature reports that there are 180 different ABCC6 mutations in PXE. The purpose of this paper is to report eight novel mutations in ABCC6 and to update the spectrum and frequency of ABCC6 mutations in PXE patients.

Methods: Eye, skin, and DNA examinations were performed using standard methodologies. We newly investigated the gene in 90 probands by denaturing high-performance liquid chromatography (dHPLC) and direct sequencing. We examined a total of 166 probands.

Results: Eight novel ABCC6 mutations (c.1685T>C, p.Met562Thr; c.2477T>C, p.Leu826Pro; c.2891G>C, p.Arg964Pro; c.3207C>A, p.Tyr1069X; c.3364delT, p.Ser1122fs; c.3717T>G, p.Tyr1293X; c.3871G>A, p.Ala1291Thr; c.4306_4312del, p.Thr1436fs) were found in seven unrelated patients. Currently, our mutation detection score is at least one ABCC6 mutation in 87% of patients with a clinical diagnosis of PXE.

Conclusions: Our results support that ABCC6 is the most important, and probably the only, causative gene of PXE. In total, 188 different ABCC6 mutations have now been reported in PXE in the literature.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2254972PMC
January 2008

Mutation analysis in a family with oculocutaneous albinism manifesting in the same generation of three branches.

Mol Vis 2007 Oct 2;13:1851-5. Epub 2007 Oct 2.

Regensburg University Medical Center, Department of Pediatric Ophthalmology, Strabismology and Ophthalmogenetics, Franz Josef Strauss, Regensburg, Germany.

Purpose: To elucidate the molecular basis of oculocutaneous albinism with variable expressivity in a family from The Netherlands in which no consanguinity was reported.

Methods: Three affected family members were screened for mutations in tyrosinase (TYR) and the pink-eye-dilution gene (P) by using SSCP. The melanocortin receptor gene (MC1R) and amplimers of P showing an aberrant banding pattern in SSCP were analyzed by direct sequencing. All participants underwent ophthalmologic examination including funduscopy, and visually evoked potentials were recorded in two cases.

Results: The pedigree had three branches A, B, and C. We identified three mutations in P (V443I, N476S, C793F) that cause a compound heterozygous situation in cases from branch A (N476S/C793F) and B (V443I/C793F), who showed oculocutaneous albinism. Hair and skin color followed the light Nordic complexion that was also present in other affected and unaffected members of this family. Descendants of branches A and B showed light complexion with iris translucency and peripheral fundus hypopigmentation independent from the genotype identified. A single descendant had red hair, carrying a well known compound MC1R mutation combination for red hair color and a single heterozygous P mutation.

Conclusions: P mutations underlie oculocutaneous albinism in this family. Two known mutations in MC1R caused red hair color in one family member. No modifier effect of MC1R on P mutations could be deduced from the results of this study.
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October 2007

L1 retrotransposition can occur early in human embryonic development.

Hum Mol Genet 2007 Jul 4;16(13):1587-92. Epub 2007 May 4.

Department of Human Genetics, Radboud University Nijmegen Medical Centre, 6500 HB Nijmegen, The Netherlands.

L1 elements are autonomous retrotransposons that can cause hereditary diseases. We have previously identified a full-length L1 insertion in the CHM (choroideremia) gene of a patient with choroideremia, an X-linked progressive eye disease. Because this L1 element, designated L1(CHM), contains two 3'-transductions, we were able to delineate a retrotransposition path in which a precursor L1 on chromosome 10p15 or 18p11 retrotransposed to chromosome 6p21 and subsequently to the CHM gene on chromosome Xq21. A cell culture retrotransposition assay showed that L1(CHM) is one of the most active L1 elements in the human genome. Most importantly, analysis of genomic DNA from the CHM patient's relatives indicated somatic and germ-line mosaicism for the L1 insertion in his mother. These findings provide evidence that L1 retrotransposition can occur very early in human embryonic development.
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http://dx.doi.org/10.1093/hmg/ddm108DOI Listing
July 2007

Germline mutation of INI1/SMARCB1 in familial schwannomatosis.

Am J Hum Genet 2007 Apr 16;80(4):805-10. Epub 2007 Feb 16.

Department of Neurogenetics, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.

Patients with schwannomatosis develop multiple schwannomas but no vestibular schwannomas diagnostic of neurofibromatosis type 2. We report an inactivating germline mutation in exon 1 of the tumor-suppressor gene INI1 in a father and daughter who both had schwannomatosis. Inactivation of the wild-type INI1 allele, by a second mutation in exon 5 or by clear loss, was found in two of four investigated schwannomas from these patients. All four schwannomas displayed complete loss of nuclear INI1 protein expression in part of the cells. Although the exact oncogenetic mechanism in these schwannomas remains to be elucidated, our findings suggest that INI1 is the predisposing gene in familial schwannomatosis.
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http://dx.doi.org/10.1086/513207DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1852715PMC
April 2007

ABCC6 and pseudoxanthoma elasticum.

Pflugers Arch 2007 Feb 8;453(5):685-91. Epub 2006 Apr 8.

Department of Clinical and Molecular Ophthalmogenetics, Amsterdam, The Netherlands.

ABCC6 belongs to the adenosine triphosphate-binding cassette (ABC) gene subfamily C. This protein family is involved in a large variety of physiological processes, such as signal transduction, protein secretion, drug and antibiotic resistance, and antigen presentation [Kool et al. (1999) 59:175-182; Borst and Elferink (2002) 71:537-592]. ABCC6 is primarily and highly expressed in the liver and kidney [Kool et al. (1999) 59:175-182; Bergen et al. (2000) 25:228-2231]. The precise physiological function and natural substrate(s) transported by ABCC6 are unknown, but the protein may be involved in active transport of intracellular compounds to the extracellular environment [Kool et al. (1999) 59:175-182] [Scheffer et al. (2002) 82:515-518]. Recently, it was shown that loss of function mutations in ABCC6 cause pseudoxanthoma elasticum (PXE) [Bergen et al. (2000) 25:228-2231; Le Saux et al. (2000) 25:223-227]. PXE is an autosomal recessively inherited multi-organ disorder [Goodman et al. (1963) 42:297-334; Lebwohl et al. (1994) 30:103-107]. PXE is primarily associated with the accumulation of mineralized and fragmented elastic fibers of the connective tissue in the skin [Neldner (1988) 6:1-159], Bruch's membrane in the retina [Hu et al. (2003) 48:424-438], and vessel walls [Kornet et al. (2004) 30:1041-1048]. PXE patients usually have skin lesions and breaks in Bruch's membrane of the retina (angioid streaks). Also, a variety of cardiovascular complications has been observed [Hu et al. (2003) 48:424-438]. Recently, a mouse model for PXE was created by targeted disruption of Abcc6 [Gorgels et al. (2005) 14:1763-1773; Klement et al. (2005) 25:8299-8310], which may be useful to elucidate the precise function of Abcc6 and to develop experimental therapies.
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http://dx.doi.org/10.1007/s00424-005-0039-0DOI Listing
February 2007

Influence of mutation type on clinical expression of Leber hereditary optic neuropathy.

Am J Ophthalmol 2006 Apr;141(4):676-82

Department of Genetics and Cell Biology, Maastricht University, Maastricht, The Netherlands.

Purpose: The aim of this research was to determine the molecular factors of influence on the clinical expression of Leber hereditary optic neuropathy (LHON), which might aid in counseling LHON patients and families. The prevalence of LHON in the Dutch population was determined.

Design: Observational, retrospective population cohort study.

Methods: The clinical characteristics of LHON patients of 25 families, previously described in 1963, were reevaluated. The mutation and haplotype were determined in the DNA of one affected LHON patient per family. The genotype of their relatives could be deducted, enabling us to evaluate retrospectively the genotype-phenotype correlation. The prevalence of LHON was determined on the basis of anamnestic evaluation of patients in 1963 and by using population registers of that period.

Results: The LHON mutation does not influence disease penetrance (50% in male subjects; 10% to 20% in female subjects). More than half of the patients with the 14484 mutation exhibit a partial recovery of vision, regardless of the acuteness of disease onset (P = .001), whereas only 22% of the 11778 carriers and 15.4% of the 3460 carriers recovered. The recovery did not take place within the first year after onset and was uncommon after four years. The onset of LHON is in general very acute but might be more gradual in 11778 carriers and in children. The calculated prevalence of LHON in the Dutch population (1/39,000) is very likely an underestimation caused by a selection bias of familial cases in the original study.

Conclusions: The LHON genotype influences the recovery of vision and disease onset but is unrelated to age, acuteness of onset, or gender. The genotype does not influence disease penetrance. Children might exhibit a slower onset of disease.
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http://dx.doi.org/10.1016/j.ajo.2005.11.007DOI Listing
April 2006

Does autosomal dominant pseudoxanthoma elasticum exist?

Am J Med Genet A 2004 May;126A(4):403-12

The Netherlands Ophthalmic Research Institute, KNAW, Amsterdam, The Netherlands.

Unlabelled: Pseudoxanthoma elasticum (PXE) is a progressive disorder of elastic fibers in skin, eyes, and arterial walls. It is caused by mutations in the ABCC6 gene. Most patients are sporadic cases. The majority of familial cases show autosomal recessive (AR) inheritance, but autosomal dominant (AD) inheritance has also been reported. We reviewed the literature on AD PXE and we studied in detail, both clinically and by DNA studies, a selection of potentially AD pedigrees from our patient population consisting of 59 probands and their family members. Individuals were considered to have definite PXE if they had two of the following three criteria: characteristic ophthalmologic signs, characteristic dermatologic signs, and a positive skin biopsy. In the literature we found only three families with definite PXE in two successive generations and no families with definite PXE in three or more generations. Our own data set comprised three putative AD families. Extensive DNA studies revealed a mutation in only one ABCC6 allele in the patients of these families. Only one of our families showed definite PXE in two generations. Linkage studies revealed that pseudodominance was unlikely in this family. In the other two families AD PXE could not be confirmed after extensive clinical examinations and application of our criteria, since definite PXE was not present in two or more generations.

Conclusion: the inheritance pattern in PXE usually is AR. Part of the phenotype in family members of PXE patients might be due to expression in heterozygous carriers of an AR disease. AD inheritance in PXE may exist, but is both after careful literature study and in our patient material much rarer than previously thought.
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http://dx.doi.org/10.1002/ajmg.a.20632DOI Listing
May 2004

Pseudoxanthoma elasticum: a clinical, histopathological, and molecular update.

Surv Ophthalmol 2003 Jul-Aug;48(4):424-38

Department of Ophthalmogenetics, The Netherlands Ophthalmic Research Institute, KNAW, Amsterdam, The Netherlands.

Pseudoxanthoma elasticum is an autosomally inherited disorder that is associated with the accumulation of mineralized and fragmented elastic fibers in the skin, Bruch's membrane in the retina, and vessel walls. The ophthalmic and dermatologic expression of pseudoxanthoma elasticum and its vascular complications are heterogeneous, with considerable variation in phenotype, progression, and mode of inheritance. Using linkage analysis and mutation detection techniques, mutations in the ABCC6 gene were recently implicated in the etiology of pseudoxanthoma elasticum. ABCC6 encodes the sixth member of the ATP-binding cassette transporter and multidrug resistance protein family (MRP6). In humans, this transmembrane protein is highly expressed in the liver and kidney. Lower expression was found in tissues affected by pseudoxanthoma elasticum, including skin, retina, and vessel walls. So far, the substrates transported by the ABCC6 protein and its physiological role in the etiology of pseudoxanthoma elasticum are not known. A functional transport study of rat MRP6 suggests that small peptides such as the endothelin receptor antagonist BQ123 are transported by MRP6. Similar molecules transported by ABCC6 in humans may be essential for extracellular matrix deposition or turnover of connective tissue at specific sites in the body. One of these sites is Bruch's membrane. This review is an update on etiology of pseudoxanthoma elasticum, including its clinical and genetic features, pathogenesis, and biomolecular basis.
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http://dx.doi.org/10.1016/s0039-6257(03)00053-5DOI Listing
October 2003