Publications by authors named "Sabine Defoort"

7 Publications

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Resolving the dark matter of ABCA4 for 1054 Stargardt disease probands through integrated genomics and transcriptomics.

Genet Med 2020 07 20;22(7):1235-1246. Epub 2020 Apr 20.

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

Purpose: Missing heritability in human diseases represents a major challenge, and this is particularly true for ABCA4-associated Stargardt disease (STGD1). We aimed to elucidate the genomic and transcriptomic variation in 1054 unsolved STGD and STGD-like probands.

Methods: Sequencing of the complete 128-kb ABCA4 gene was performed using single-molecule molecular inversion probes (smMIPs), based on a semiautomated and cost-effective method. Structural variants (SVs) were identified using relative read coverage analyses and putative splice defects were studied using in vitro assays.

Results: In 448 biallelic probands 14 known and 13 novel deep-intronic variants were found, resulting in pseudoexon (PE) insertions or exon elongations in 105 alleles. Intriguingly, intron 13 variants c.1938-621G>A and c.1938-514G>A resulted in dual PE insertions consisting of the same upstream, but different downstream PEs. The intron 44 variant c.6148-84A>T resulted in two PE insertions and flanking exon deletions. Eleven distinct large deletions were found, two of which contained small inverted segments. Uniparental isodisomy of chromosome 1 was identified in one proband.

Conclusion: Deep sequencing of ABCA4 and midigene-based splice assays allowed the identification of SVs and causal deep-intronic variants in 25% of biallelic STGD1 cases, which represents a model study that can be applied to other inherited diseases.
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July 2020

Cost-effective molecular inversion probe-based ABCA4 sequencing reveals deep-intronic variants in Stargardt disease.

Hum Mutat 2019 10 18;40(10):1749-1759. Epub 2019 Jun 18.

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

Purpose: Stargardt disease (STGD1) is caused by biallelic mutations in ABCA4, but many patients are genetically unsolved due to insensitive mutation-scanning methods. We aimed to develop a cost-effective sequencing method for ABCA4 exons and regions carrying known causal deep-intronic variants.

Methods: Fifty exons and 12 regions containing 14 deep-intronic variants of ABCA4 were sequenced using double-tiled single molecule Molecular Inversion Probe (smMIP)-based next-generation sequencing. DNAs of 16 STGD1 cases carrying 29 ABCA4 alleles and of four healthy persons were sequenced using 483 smMIPs. Thereafter, DNAs of 411 STGD1 cases with one or no ABCA4 variant were sequenced. The effect of novel noncoding variants on splicing was analyzed using in vitro splice assays.

Results: Thirty-four ABCA4 variants previously identified in 16 STGD1 cases were reliably identified. In 155/411 probands (38%), two causal variants were identified. We identified 11 deep-intronic variants present in 62 alleles. Two known and two new noncanonical splice site variants showed splice defects, and one novel deep-intronic variant (c.4539+2065C>G) resulted in a 170-nt mRNA pseudoexon insertion (p.[Arg1514Lysfs*35,=]).

Conclusions: smMIPs-based sequence analysis of coding and selected noncoding regions of ABCA4 enabled cost-effective mutation detection in STGD1 cases in previously unsolved cases.
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October 2019

Donepezil increases contrast sensitivity for the detection of objects in scenes.

Behav Brain Res 2015 Oct 7;292:443-7. Epub 2015 Jul 7.

U1171, Université de Lille, INSERM, Centre Hospitalier et Universitaire, Lille, France.

We assessed the effects of donepezil, a drug that stimulates cholinergic transmission, and scopolamine, an antagonist of cholinergic transmission, on contrast sensitivity. 30 young male participants were tested under three treatment conditions: placebo, donepezil, and scopolamine in a random order. Pairs of photographs varying in contrast were displayed left and right of fixation for 50 ms. Participants were asked to locate the scene containing an animal. Accuracy was better under donepezil than under scopolamine, particularly for signals of high intensity (at higher levels of contrast). A control experiment showed that the lower performance under scopolamine did not result from the mydriasis induced by scopolamine. The results suggest that cholinergic stimulation, through donepezil, facilitates signal detection in agreement with studies on animals showing that the pharmacological activation of cholinergic receptors controls the gain in the relationship between the stimulus contrast (intensity of the visual input) and visual response. As Alzheimer disease is associated to depletion in acetylcholine, and there is evidence of deficits in contrast sensitivity in Alzheimer, it might be interesting to integrate such rapid and sensitive visual tasks in the biomarkers at early stage of drug development.
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October 2015

Further delineation of eye manifestations in homozygous 15q13.3 microdeletions including TRPM1: a differential diagnosis of ceroid lipofuscinosis.

Am J Med Genet A 2014 Jun 25;164A(6):1537-44. Epub 2014 Mar 25.

Centre de Génétique et Centre de Référence Anomalies du Développement et Syndromes Malformatifs, Hôpital d'Enfants, CHU Dijon, France.

The 15q13.3 heterozygous microdeletion is a fairly common microdeletion syndrome with marked clinical variability and incomplete penetrance. The average size of the deletion, which comprises six genes including CHRNA7, is 1.5 Mb. CHRNA7 has been identified as the gene responsible for the neurological phenotype in this microdeletion syndrome. Only seven patients with a homozygous microdeletion that includes at least CHRNA7, and is inherited from both parents have been described in the literature. The aim of this study was to further describe the distinctive eye manifestations from the analysis in the three French patients diagnosed with the classical 1.5 Mb homozygous microdeletion. Patients' ages ranged from 30 months to 9 years, and included one sib pair. They all displayed a remarkably severe identifiable clinical phenotype that included congenital blindness and convulsive encephalopathy with inconstant abnormal movements. The ophthalmological examination revealed a lack of eye tracking, optic nerve pallor, an immature response with increased latencies with no response to the checkerboard stimulations at the visual evoked potential examination, and a distinctive retina dystrophy with a negative electroretinogram in which the "b" wave was smaller than the "a" wave after a dark adapted pupil and bright flash in all patients. Clear genotype-phenotype correlations emerged, showing that this eye phenotype was secondary to homozygous deletion of TRPM1, the gene responsible for autosomal recessive congenital stationary night blindness. The main differential diagnosis is ceroid lipofuscinosis.
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June 2014

Optical coherence tomography in clinically isolated syndrome: no evidence of subclinical retinal axonal loss.

Arch Neurol 2009 Nov;66(11):1373-7

Department of Neurology, Université Lille Nord de France, Lille, France.

Background: Optical coherence tomography has emerged as a new tool for quantifying axonal loss in multiple sclerosis (MS). A reduction in retinal nerve fiber layer (RNFL) thickness is correlated with Expanded Disability Status Scale score and brain atrophy.

Objective: To investigate RNFL and macular volume measurements using optical coherence tomography in the clinically isolated syndrome population.

Design: Prospective case series. Settings Neurologic clinics at the university hospitals of Lille and Strasbourg (France).

Participants: Fifty-six consecutive patients with clinically isolated syndrome (18 with optic neuritis and 38 without optic neuritis) and 32 control subjects.

Main Outcome Measures: Macular volume and RNFL thickness.

Results: Mean (SD) overall RNFL thickness (98.98 [10.26] microm) and macular volume (6.86 [0.32] microm(3)) in the clinically isolated syndrome population were not significantly different compared with the controls (98.71 [9.08] mum and 6.92 [0.38] microm(3), respectively). No link was noted between atrophy of the RNFL or macula and conversion to MS at 6 months.

Conclusions: Optical coherence tomography does not reveal retinal axonal loss at the earliest clinical stage of MS and does not predict conversion to MS at 6 months.
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November 2009

Molecular screening of 980 cases of suspected hereditary optic neuropathy with a report on 77 novel OPA1 mutations.

Hum Mutat 2009 Jul;30(7):E692-705

INSERM, U694, Angers, F-49000, France.

We report the results of molecular screening in 980 patients carried out as part of their work-up for suspected hereditary optic neuropathies. All the patients were investigated for Leber's hereditary optic neuropathy (LHON) and autosomal dominant optic atrophy (ADOA), by searching for the ten primary LHON-causing mtDNA mutations and examining the entire coding sequences of the OPA1 and OPA3 genes, the two genes currently identified in ADOA. Molecular defects were identified in 440 patients (45% of screened patients). Among these, 295 patients (67%) had an OPA1 mutation, 131 patients (30%) had an mtDNA mutation, and 14 patients (3%), belonging to three unrelated families, had an OPA3 mutation. Interestingly, OPA1 mutations were found in 157 (40%) of the 392 apparently sporadic cases of optic atrophy. The eOPA1 locus-specific database now contains a total of 204 OPA1 mutations, including 77 novel OPA1 mutations reported here. The statistical analysis of this large set of mutations has led us to propose a diagnostic strategy that should help with the molecular work-up of optic neuropathies. Our results highlight the importance of investigating LHON-causing mtDNA mutations as well as OPA1 and OPA3 mutations in cases of suspected hereditary optic neuropathy, even in absence of a family history of the disease.
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July 2009

Optical coherence tomography in neuromyelitis optica.

Arch Neurol 2008 Jul;65(7):920-3

Department of Neurology, Strasbourg University, Hôpital Civil, 1 Place de l'Hôpital, BP 426, 67091 Strasbourg CEDEX, France.

Background: Neuromyelitis optica (NMO) is an inflammatory disease with combined features of optic neuritis and myelitis. This pathologic entity may induce severe disability, including visual loss and paraplegia. Other than clinical follow-up, there is no marker for severity of the disease.

Objectives: To evaluate the use of optical coherence tomography (OCT) in NMO and to determine whether this new technique could be a good marker of axonal loss in NMO.

Design: Cross-sectional study.

Participants: Thirty-five patients with NMO or at a high risk for NMO (having optic neuritis or myelitis and who are positive for NMO antibody) were prospectively studied. Fifteen healthy individuals served as control subjects.

Main Outcome Measure: All patients underwent a complete ophthalmologic evaluation, including OCT, funduscopy, and visual field, visual acuity, and visual evoked potential testing. Expanded Disability Status Scale scores were assessed but without the visual data. Correlations between the visual test results and demographic or clinical characteristics were evaluated.

Results: Optical coherence tomography and visual field data were available for only 32 patients because 3 patients were blind. The mean retinal nerve fiber layer thickness was significantly reduced in patients with NMO compared with controls (P < .001). We found good correlation between the OCT results and visual field testing. We also found weak correlation between OCT results and both visual acuity and visual evoked potential latencies. We did not find any correlation between OCT results and age, sex, or disease duration. In contrast, retinal nerve fiber layer thickness was closely correlated with the Expanded Disability Status Scale score (P < .001).

Conclusions: Optical coherence tomography results are significantly altered in patients with NMO. Optical coherence tomography is easy to perform, and the results are well correlated with visual acuity and visual field findings. It could be considered a marker of axonal loss because we found good correlation between OCT and the Expanded Disability Status Scale score. These preliminary results will need to be confirmed in a longitudinal prospective study.
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July 2008