Publications by authors named "Bert L Callewaert"

14 Publications

  • Page 1 of 1

Defining the genotypic and phenotypic spectrum of X-linked MSL3-related disorder.

Genet Med 2021 Feb 11;23(2):384-395. Epub 2020 Nov 11.

Institute of Human Genetics, Technical University Munich, Munich, Germany.

Purpose: We sought to delineate the genotypic and phenotypic spectrum of female and male individuals with X-linked, MSL3-related disorder (Basilicata-Akhtar syndrome).

Methods: Twenty-five individuals (15 males, 10 females) with causative variants in MSL3 were ascertained through exome or genome sequencing at ten different sequencing centers.

Results: We identified multiple variant types in MSL3 (ten nonsense, six frameshift, four splice site, three missense, one in-frame-deletion, one multi-exon deletion), most proven to be de novo, and clustering in the terminal eight exons suggesting that truncating variants in the first five exons might be compensated by an alternative MSL3 transcript. Three-dimensional modeling of missense and splice variants indicated that these have a deleterious effect. The main clinical findings comprised developmental delay and intellectual disability ranging from mild to severe. Autism spectrum disorder, muscle tone abnormalities, and macrocephaly were common as well as hearing impairment and gastrointestinal problems. Hypoplasia of the cerebellar vermis emerged as a consistent magnetic resonance image (MRI) finding. Females and males were equally affected. Using facial analysis technology, a recognizable facial gestalt was determined.

Conclusion: Our aggregated data illustrate the genotypic and phenotypic spectrum of X-linked, MSL3-related disorder (Basilicata-Akhtar syndrome). Our cohort improves the understanding of disease related morbidity and allows us to propose detailed surveillance guidelines for affected individuals.
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http://dx.doi.org/10.1038/s41436-020-00993-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7862064PMC
February 2021

Decreased Nuclear Ascorbate Accumulation Accompanied with Altered Genomic Methylation Pattern in Fibroblasts from Arterial Tortuosity Syndrome Patients.

Oxid Med Cell Longev 2019 13;2019:8156592. Epub 2019 Jan 13.

Institute of Clinical Experimental Research, Semmelweis University, Budapest 1094, Hungary.

Ascorbate requiring Fe/2-oxoglutarate-dependent dioxygenases located in the nucleoplasm have been shown to participate in epigenetic regulation of gene expression via histone and DNA demethylation. Transport of dehydroascorbic acid is impaired in the endomembranes of fibroblasts from arterial tortuosity syndrome (ATS) patients, due to the mutation in the gene coding for glucose transporter GLUT10. We hypothesized that altered nuclear ascorbate concentration might be present in ATS fibroblasts, affecting dioxygenase activity and DNA demethylation. Therefore, our aim was to characterize the subcellular distribution of vitamin C, the global and site-specific changes in 5-methylcytosine and 5-hydroxymethylcytosine levels, and the effect of ascorbate supplementation in control and ATS fibroblast cultures. Diminished nuclear accumulation of ascorbate was found in ATS fibroblasts upon ascorbate or dehydroascorbic acid addition. Analyzing DNA samples of cultured fibroblasts from controls and ATS patients, a lower global 5-hydroxymethylcytosine level was found in ATS fibroblasts, which could not be significantly modified by ascorbate addition. Investigation of the (hydroxy)methylation status of specific regions in six candidate genes related to ascorbate metabolism and function showed that ascorbate addition could stimulate hydroxymethylation and active DNA demethylation at the PPAR- gene region in control fibroblasts only. The altered DNA hydroxymethylation patterns in patient cells both at the global level and at specific gene regions accompanied with decreased nuclear accumulation of ascorbate suggests the epigenetic role of vitamin C in the pathomechanism of ATS. The present findings represent the first example for the role of vitamin C transport in epigenetic regulation suggesting that ATS is a compartmentalization disease.
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http://dx.doi.org/10.1155/2019/8156592DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6360052PMC
March 2019

Clinical Validity of Genes for Heritable Thoracic Aortic Aneurysm and Dissection.

J Am Coll Cardiol 2018 08;72(6):605-615

Center for Medical Genetics, Ghent University Hospital, Ghent, Belgium; Department of Cardiology, Ghent University Hospital, Ghent, Belgium. Electronic address:

Background: Thoracic aortic aneurysms progressively enlarge and predispose to acute aortic dissections. Up to 25% of individuals with thoracic aortic disease harbor an underlying Mendelian pathogenic variant. An evidence-based strategy for selection of genes to test in hereditary thoracic aortic aneurysm and dissection (HTAAD) helps inform family screening and intervention to prevent life-threatening thoracic aortic events.

Objectives: The purpose of this study was to accurately identify genes that predispose to HTAAD using the Clinical Genome Resource (ClinGen) framework.

Methods: We applied the semiquantitative ClinGen framework to assess presumed gene-disease relationships between 53 candidate genes and HTAAD. Genes were classified as causative for HTAAD if they were associated with isolated thoracic aortic disease and were clinically actionable, triggering routine aortic surveillance, intervention, and family cascade screening. All gene-disease assertions were evaluated by a pre-defined curator-expert pair and subsequently discussed with an expert panel.

Results: Genes were classified based on the strength of association with HTAAD into 5 categories: definitive (n = 9), strong (n = 2), moderate (n = 4), limited (n = 15), and no reported evidence (n = 23). They were further categorized by severity of associated aortic disease and risk of progression. Eleven genes in the definitive and strong groups were designated as "HTAAD genes" (category A). Eight genes were classified as unlikely to be progressive (category B) and 4 as low risk (category C). The remaining genes were recent genes with an uncertain classification or genes with no evidence of association with HTAAD.

Conclusions: The ClinGen framework is useful to semiquantitatively assess the strength of gene-disease relationships for HTAAD. Gene categories resulting from the curation may inform clinical laboratories in the development, interpretation, and subsequent clinical implications of genetic testing for patients with aortic disease.
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http://dx.doi.org/10.1016/j.jacc.2018.04.089DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6378369PMC
August 2018

Diagnosis of multiple endocrine neoplasia type 2B and management of its ocular features.

Ophthalmic Genet 2018 04 28;39(2):268-270. Epub 2017 Nov 28.

c Center for Medical Genetics , Ghent University Hospital , Ghent , Belgium.

Background: To describe ocular and vascular findings in a patient with multiple endocrine neoplasia type 2B.

Materials And Methods: Case report of a 31-year-old male who was referred for ocular assessment following diagnosis of a carotid artery dissection and multiple vascular anomalies.

Results: Clinical examination revealed a marfanoid habitus, myelinated corneal nerve fibers, neuromas in the perilimbal area, conjunctival hyperemia with peripheral corneal neovascularization, and posterior blepharitis. Diagnosis of multiple endocrine neoplasia type 2B was confirmed by genetic testing of the RET proto-oncogene. Genetic screening for hereditary aortic and peripheral vasculopathies failed to reveal an underlying cause for the vascular findings. We noted improvement of the ocular surface disease with topical corticosteroids and oral tetracyclines.

Conclusions: Ophthalmologists play a vital role in recognizing this rare but lethal malignancy. We report on a patient with apart from characteristic ocular findings also staphylococcal hypersensitivity and widespread systemic vasculopathy.
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http://dx.doi.org/10.1080/13816810.2017.1408849DOI Listing
April 2018

GLUT10-Lacking in Arterial Tortuosity Syndrome-Is Localized to the Endoplasmic Reticulum of Human Fibroblasts.

Int J Mol Sci 2017 Aug 22;18(8). Epub 2017 Aug 22.

Division of Biology and Genetics, Department of Molecular and Translational Medicine, University of Brescia, 25123 Brescia, Italy.

GLUT10 belongs to a family of transporters that catalyze the uptake of sugars/polyols by facilitated diffusion. Loss-of-function mutations in the gene encoding GLUT10 are responsible for arterial tortuosity syndrome (ATS). Since subcellular distribution of the transporter is dubious, we aimed to clarify the localization of GLUT10. In silico GLUT10 localization prediction suggested its presence in the endoplasmic reticulum (ER). Immunoblotting showed the presence of GLUT10 protein in the microsomal, but not in mitochondrial fractions of human fibroblasts and liver tissue. An even cytosolic distribution with an intense perinuclear decoration of GLUT10 was demonstrated by immunofluorescence in human fibroblasts, whilst mitochondrial markers revealed a fully different decoration pattern. GLUT10 decoration was fully absent in fibroblasts from three ATS patients. Expression of exogenous, tagged GLUT10 in fibroblasts from an ATS patient revealed a strict co-localization with the ER marker protein disulfide isomerase (PDI). The results demonstrate that GLUT10 is present in the ER.
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http://dx.doi.org/10.3390/ijms18081820DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5578206PMC
August 2017

Glucose transporter type 10-lacking in arterial tortuosity syndrome-facilitates dehydroascorbic acid transport.

FEBS Lett 2016 Jun 27;590(11):1630-40. Epub 2016 May 27.

Institute of Clinical Experimental Research, Semmelweis University, Budapest, Hungary.

Loss-of-function mutations in the gene encoding GLUT10 are responsible for arterial tortuosity syndrome (ATS), a rare connective tissue disorder. In this study GLUT10-mediated dehydroascorbic acid (DAA) transport was investigated, supposing its involvement in the pathomechanism. GLUT10 protein produced by in vitro translation and incorporated into liposomes efficiently transported DAA. Silencing of GLUT10 decreased DAA transport in immortalized human fibroblasts whose plasma membrane was selectively permeabilized. Similarly, the transport of DAA through endomembranes was markedly reduced in fibroblasts from ATS patients. Re-expression of GLUT10 in patients' fibroblasts restored DAA transport activity. The present results demonstrate that GLUT10 is a DAA transporter and DAA transport is diminished in the endomembranes of fibroblasts from ATS patients.
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http://dx.doi.org/10.1002/1873-3468.12204DOI Listing
June 2016

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

GLUT10 is required for the development of the cardiovascular system and the notochord and connects mitochondrial function to TGFβ signaling.

Hum Mol Genet 2012 Mar 24;21(6):1248-59. Epub 2011 Nov 24.

Department of Pediatrics, Washington University School of Medicine, St. Louis, MO, USA.

Growth factor signaling results in dramatic phenotypic changes in cells, which require commensurate alterations in cellular metabolism. Mutations in SLC2A10/GLUT10, a member of the facilitative glucose transporter family, are associated with altered transforming growth factor-β (TGFβ) signaling in patients with arterial tortuosity syndrome (ATS). The objective of this work was to test whether SLC2A10/GLUT10 can serve as a link between TGFβ-related transcriptional regulation and metabolism during development. In zebrafish embryos, knockdown of slc2a10 using antisense morpholino oligonucleotide injection caused a wavy notochord and cardiovascular abnormalities with a reduced heart rate and blood flow, which was coupled with an incomplete and irregular vascular patterning. This was phenocopied by treatment with a small-molecule inhibitor of TGFβ receptor (tgfbr1/alk5). Array hybridization showed that the changes at the transcriptome level caused by the two treatments were highly correlated, revealing that a reduced tgfbr1 signaling is a key feature of ATS in early zebrafish development. Interestingly, a large proportion of the genes, which were specifically dysregulated after glut10 depletion gene and not by tgfbr1 inhibition, play a major role in mitochondrial function. Consistent with these results, slc2a10 morphants showed decreased respiration and reduced TGFβ reporter gene activity. Finally, co-injection of antisense morpholinos targeting slc2a10 and smad7 (a TGFβ inhibitor) resulted in a partial rescue of smad7 morphant phenotypes, suggesting scl2a10/glut10 functions downstream of smads. Taken together, glut10 is essential for cardiovascular development by facilitating both mitochondrial respiration and TGFβ signaling.
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http://dx.doi.org/10.1093/hmg/ddr555DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3284116PMC
March 2012

The revised Ghent nosology for the Marfan syndrome.

J Med Genet 2010 Jul;47(7):476-85

Center for Medical Genetics, Ghent University Hospital, De Pintelaan 185, Gent, Belgium.

The diagnosis of Marfan syndrome (MFS) relies on defined clinical criteria (Ghent nosology), outlined by international expert opinion to facilitate accurate recognition of this genetic aneurysm syndrome and to improve patient management and counselling. These Ghent criteria, comprising a set of major and minor manifestations in different body systems, have proven to work well since with improving molecular techniques, confirmation of the diagnosis is possible in over 95% of patients. However, concerns with the current nosology are that some of the diagnostic criteria have not been sufficiently validated, are not applicable in children or necessitate expensive and specialised investigations. The recognition of variable clinical expression and the recently extended differential diagnosis further confound accurate diagnostic decision making. Moreover, the diagnosis of MFS--whether or not established correctly--can be stigmatising, hamper career aspirations, restrict life insurance opportunities, and cause psychosocial burden. An international expert panel has established a revised Ghent nosology, which puts more weight on the cardiovascular manifestations and in which aortic root aneurysm and ectopia lentis are the cardinal clinical features. In the absence of any family history, the presence of these two manifestations is sufficient for the unequivocal diagnosis of MFS. In absence of either of these two, the presence of a bonafide FBN1 mutation or a combination of systemic manifestations is required. For the latter a new scoring system has been designed. In this revised nosology, FBN1 testing, although not mandatory, has greater weight in the diagnostic assessment. Special considerations are given to the diagnosis of MFS in children and alternative diagnoses in adults. We anticipate that these new guidelines may delay a definitive diagnosis of MFS but will decrease the risk of premature or misdiagnosis and facilitate worldwide discussion of risk and follow-up/management guidelines.
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http://dx.doi.org/10.1136/jmg.2009.072785DOI Listing
July 2010

Altered TGFbeta signaling and cardiovascular manifestations in patients with autosomal recessive cutis laxa type I caused by fibulin-4 deficiency.

Eur J Hum Genet 2010 Aug 14;18(8):895-901. Epub 2010 Apr 14.

Center for Medical Genetics, University Hospital Ghent, De Pintelaan 185, Ghent, Belgium.

Fibulin-4 is a member of the fibulin family, a group of extracellular matrix proteins prominently expressed in medial layers of large veins and arteries. Involvement of the FBLN4 gene in cardiovascular pathology was shown in a murine model and in three patients affected with cutis laxa in association with systemic involvement. To elucidate the contribution of FBLN4 in human disease, we investigated two cohorts of patients. Direct sequencing of 17 patients with cutis laxa revealed no FBLN4 mutations. In a second group of 22 patients presenting with arterial tortuosity, stenosis and aneurysms, FBLN4 mutations were identified in three patients, two homozygous missense mutations (p.Glu126Lys and p.Ala397Thr) and compound heterozygosity for missense mutation p.Glu126Val and frameshift mutation c.577delC. Immunoblotting analysis showed a decreased amount of fibulin-4 protein in the fibroblast culture media of two patients, a finding sustained by diminished fibulin-4 in the extracellular matrix of the aortic wall on immunohistochemistry. pSmad2 and CTGF immunostaining of aortic and lung tissue revealed an increase in transforming growth factor (TGF)beta signaling. This was confirmed by pSmad2 immunoblotting of fibroblast cultures. In conclusion, patients with recessive FBLN4 mutations are predominantly characterized by aortic aneurysms, arterial tortuosity and stenosis. This confirms the important role of fibulin-4 in vascular elastic fiber assembly. Furthermore, we provide the first evidence for the involvement of altered TGFbeta signaling in the pathogenesis of FBLN4 mutations in humans.
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http://dx.doi.org/10.1038/ejhg.2010.45DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2987390PMC
August 2010

Clinical and molecular study of 320 children with Marfan syndrome and related type I fibrillinopathies in a series of 1009 probands with pathogenic FBN1 mutations.

Pediatrics 2009 Jan;123(1):391-8

Genetic Center, Centre Hospitalier Universitaire Dijon, Dijon, France.

From a large series of 1009 probands with pathogenic FBN1 mutations, data for 320 patients <18 years of age at the last follow-up evaluation were analyzed (32%). At the time of diagnosis, the median age was 6.5 years. At the last examination, the population was classified as follows: neonatal Marfan syndrome, 14%; severe Marfan syndrome, 19%; classic Marfan syndrome, 32%; probable Marfan syndrome, 35%. Seventy-one percent had ascending aortic dilation, 55% ectopia lentis, and 28% major skeletal system involvement. Even when aortic complications existed in childhood, the rates of aortic surgery and aortic dissection remained low (5% and 1%, respectively). Some diagnostic features (major skeletal system involvement, striae, dural ectasia, and family history) were more frequent in the 10- to <18-year age group, whereas others (ascending aortic dilation and mitral abnormalities) were more frequent in the population with neonatal Marfan syndrome. Only 56% of children could be classified as having Marfan syndrome, according to international criteria, at their last follow-up evaluation when the presence of a FBN1 mutation was not considered as a major feature, with increasing frequency in the older age groups. Eighty-five percent of child probands fulfilled international criteria after molecular studies, which indicates that the discovery of a FBN1 mutation can be a valuable diagnostic aid in uncertain cases. The distributions of mutation types and locations in this pediatric series revealed large proportions of probands carrying mutations located in exons 24 to 32 (33%) and in-frame mutations (75%). Apart from lethal neonatal Marfan syndrome, we confirm that the majority of clinical manifestations of Marfan syndrome increase with age, which emphasizes the poor applicability of the international criteria to this diagnosis in childhood and the need for follow-up monitoring in cases of clinical suspicion of Marfan syndrome.
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http://dx.doi.org/10.1542/peds.2008-0703DOI Listing
January 2009

Comprehensive clinical and molecular assessment of 32 probands with congenital contractural arachnodactyly: report of 14 novel mutations and review of the literature.

Hum Mutat 2009 Mar;30(3):334-41

Center for Medical Genetics, Ghent University Hospital, Belgium.

Beals-Hecht syndrome or congenital contractural arachnodactyly (CCA) is a rare, autosomal dominant connective tissue disorder characterized by crumpled ears, arachnodactyly, contractures, and scoliosis. Recent reports also mention aortic root dilatation, a finding previously thought to differentiate the condition from Marfan syndrome (MFS). In many cases, the condition is caused by mutations in the fibrillin 2 gene (FBN2) with 26 mutations reported so far, all located in the middle region of the gene (exons 23-34). We directly sequenced the entire FBN2 gene in 32 probands clinically diagnosed with CCA. In 14 probands, we found 13 new and one previously described FBN2 mutation including a mutation in exon 17, expanding the region in which FBN2 mutations occur in CCA. Review of the literature showed that the phenotype of the FBN2 positive patients was comparable to all previously published FBN2-positive patients. In our FBN2-positive patients, cardiovascular involvement included mitral valve prolapse in two adult patients and aortic root enlargement in three patients. Whereas the dilatation regressed in one proband, it remained marked in a child proband (z-score: 4.09) and his father (z-score: 2.94), warranting echocardiographic follow-up. We confirm paradoxical patellar laxity and report keratoconus, shoulder muscle hypoplasia, and pyeloureteral junction stenosis as new features. In addition, we illustrate large intrafamilial variability. Finally, the FBN2-negative patients in this cohort were clinically indistinguishable from all published FBN2-positive patients harboring a FBN2 mutation, suggesting locus heterogeneity.
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http://dx.doi.org/10.1002/humu.20854DOI Listing
March 2009

Aneurysm syndromes caused by mutations in the TGF-beta receptor.

N Engl J Med 2006 Aug;355(8):788-98

McKusick-Nathans Institute for Genetic Medicine, Johns Hopkins University School of Medicine, and the Kennedy Krieger Institute, Baltimore, USA.

Background: The Loeys-Dietz syndrome is a recently described autosomal dominant aortic-aneurysm syndrome with widespread systemic involvement. The disease is characterized by the triad of arterial tortuosity and aneurysms, hypertelorism, and bifid uvula or cleft palate and is caused by heterozygous mutations in the genes encoding transforming growth factor beta receptors 1 and 2 (TGFBR1 and TGFBR2, respectively).

Methods: We undertook the clinical and molecular characterization of 52 affected families. Forty probands presented with typical manifestations of the Loeys-Dietz syndrome. In view of the phenotypic overlap between this syndrome and vascular Ehlers-Danlos syndrome, we screened an additional cohort of 40 patients who had vascular Ehlers-Danlos syndrome without the characteristic type III collagen abnormalities or the craniofacial features of the Loeys-Dietz syndrome.

Results: We found a mutation in TGFBR1 or TGFBR2 in all probands with typical Loeys-Dietz syndrome (type I) and in 12 probands presenting with vascular Ehlers-Danlos syndrome (Loeys-Dietz syndrome type II). The natural history of both types was characterized by aggressive arterial aneurysms (mean age at death, 26.0 years) and a high incidence of pregnancy-related complications (in 6 of 12 women). Patients with Loeys-Dietz syndrome type I, as compared with those with type II, underwent cardiovascular surgery earlier (mean age, 16.9 years vs. 26.9 years) and died earlier (22.6 years vs. 31.8 years). There were 59 vascular surgeries in the cohort, with one death during the procedure. This low rate of intraoperative mortality distinguishes the Loeys-Dietz syndrome from vascular Ehlers-Danlos syndrome.

Conclusions: Mutations in either TGFBR1 or TGFBR2 predispose patients to aggressive and widespread vascular disease. The severity of the clinical presentation is predictive of the outcome. Genotyping of patients presenting with symptoms like those of vascular Ehlers-Danlos syndrome may be used to guide therapy, including the use and timing of prophylactic vascular surgery.
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http://dx.doi.org/10.1056/NEJMoa055695DOI Listing
August 2006