Publications by authors named "Marjo S van der Knaap"

282 Publications

Expanded phenotype of AARS1-related white matter disease.

Genet Med 2021 Dec 27;23(12):2352-2359. Epub 2021 Aug 27.

Department of Neuropediatrics, Jena University Hospital, Jena, Germany.

Purpose: Recent reports of individuals with cytoplasmic transfer RNA (tRNA) synthetase-related disorders have identified cases with phenotypic variability from the index presentations. We sought to assess phenotypic variability in individuals with AARS1-related disease.

Methods: A cross-sectional survey was performed on individuals with biallelic variants in AARS1. Clinical data, neuroimaging, and genetic testing results were reviewed. Alanyl tRNA synthetase (AlaRS) activity was measured in available fibroblasts.

Results: We identified 11 affected individuals. Two phenotypic presentations emerged, one with early infantile-onset disease resembling the index cases of AARS1-related epileptic encephalopathy with deficient myelination (n = 7). The second (n = 4) was a later-onset disorder, where disease onset occurred after the first year of life and was characterized on neuroimaging by a progressive posterior predominant leukoencephalopathy evolving to include the frontal white matter. AlaRS activity was significantly reduced in five affected individuals with both early infantile-onset and late-onset phenotypes.

Conclusion: We suggest that variants in AARS1 result in a broader clinical spectrum than previously appreciated. The predominant form results in early infantile-onset disease with epileptic encephalopathy and deficient myelination. However, a subgroup of affected individuals manifests with late-onset disease and similarly rapid progressive clinical decline. Longitudinal imaging and clinical follow-up will be valuable in understanding factors affecting disease progression and outcome.
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http://dx.doi.org/10.1038/s41436-021-01286-8DOI Listing
December 2021

Biallelic PI4KA variants cause neurological, intestinal and immunological disease.

Brain 2021 Aug 20. Epub 2021 Aug 20.

Department of Pediatrics, Sana Kliniken Duisburg, Germany.

Phosphatidylinositol 4-kinase IIIα (PI4KIIIα/PI4KA/OMIM:600286) is a lipid kinase generating phosphatidylinositol 4-phosphate (PI4P), a membrane phospholipid with critical roles in the physiology of multiple cell types. PI4KIIIα's role in PI4P generation requires its assembly into a heterotetrameric complex with EFR3, TTC7 and FAM126. Sequence alterations in two of these molecular partners, TTC7 (encoded by TTC7A or TCC7B) and FAM126, have been associated with a heterogeneous group of either neurological (FAM126A) or intestinal and immunological (TTC7A) conditions. Here we show that biallelic PI4KA sequence alterations in humans are associated with neurological disease, in particular hypomyelinating leukodystrophy. In addition, affected individuals may present with inflammatory bowel disease, multiple intestinal atresia and combined immunodeficiency. Our cellular, biochemical and structural modelling studies indicate that PI4KA-associated phenotypical outcomes likely stem from impairment of molecular roles requiring organ specific PI4KIIIα-TTC7-FAM126 complex functional interactions. Together these data define PI4KA gene alteration as a cause of a variable phenotypical spectrum and provide fundamental new insight into the combinatorial biology of the PI4KIIIα-FAM126-TTC7-EFR3 molecular complex.
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http://dx.doi.org/10.1093/brain/awab313DOI Listing
August 2021

Neurofilament light chain and glial fibrillary acidic protein levels in metachromatic leukodystrophy.

Brain 2021 Aug 16. Epub 2021 Aug 16.

Amsterdam Leukodystrophy Center, Department of Child Neurology, Emma Children's Hospital, Amsterdam University Medical Centers, Vrije Universiteit Amsterdam, Amsterdam Neuroscience, 1081 HV Amsterdam, The Netherlands.

Metachromatic leukodystrophy is a lethal metabolic leukodystrophy, with emerging treatments for early disease stages. Biomarkers to measure disease activity are required for clinical assessment and treatment follow-up. This retrospective study compared neurofilament light chain and glial fibrillary acidic protein levels in CSF (n = 11) and blood (n = 92) samples of 40 patients with metachromatic leukodystrophy (aged 0-42 years) with 38 neurologically healthy children (aged 0-17 years) and 38 healthy adults (aged 18-45 years), and analyzed the associations between these levels with clinical phenotype and disease evolution in untreated and transplanted patients. Metachromatic leukodystrophy subtype was determined based on the (expected) age of symptom onset. Disease activity was assessed by measuring gross motor function deterioration and brain MRI. Longitudinal analyses with measurements up to 23 years after diagnosis were performed using linear mixed models. CSF and blood neurofilament light chain and glial fibrillary acidic protein levels in pediatric controls were negatively associated with age (all P < 0.001). Blood neurofilament light chain level at diagnosis (median, interquartile range; picogram per milliliter) was significantly increased in both pre-symptomatic (14.7, 10.6-56.7) and symptomatic patients (136, 40.8-445) compared to controls (5.6, 4.5-7.1), and highest amongst patients with late-infantile (456, 201-854) or early-juvenile MLD (291.0, 104-445) and those ineligible for treatment based on best practice (291, 57.4-472). Glial fibrillary acidic protein level (median, interquartile range; picogram per milliliter) was only increased in symptomatic patients (591, 224-1150) compared to controls (119, 78.2-338) and not significantly associated with treatment eligibility (P = 0.093). Higher blood neurofilament light chain and glial fibrillary acidic protein levels at diagnosis were associated with rapid disease progression in late-infantile (P = 0.006 and P = 0.051, respectively) and early-juvenile patients (P = 0.048 and P = 0.039, respectively). Finally, blood neurofilament light chain and glial fibrillary acidic protein levels decreased during follow-up in untreated and transplanted patients but remained elevated compared with controls. Only neurofilament light chain levels were associated with MRI deterioration (P < 0.001). This study indicates that both proteins may be considered as non-invasive biomarkers for clinical phenotype and disease stage at clinical assessment, and that neurofilament light chain might enable neurologists to make better informed treatment decisions. In addition, neurofilament light chain holds promise assessing treatment response. Importantly, both biomarkers require pediatric reference values, given that their levels first decrease before increasing with advancing age.
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http://dx.doi.org/10.1093/brain/awab304DOI Listing
August 2021

Imaging in X-Linked Adrenoleukodystrophy.

Neuropediatrics 2021 08 30;52(4):252-260. Epub 2021 Jun 30.

Department of Pediatric Neurology, Amsterdam Leukodystrophy Center, Emma Children's Hospital, Amsterdam University Medical Centers, Amsterdam Neuroscience, Amsterdam, The Netherlands.

Magnetic resonance imaging (MRI) is the gold standard for the detection of cerebral lesions in X-linked adrenoleukodystrophy (ALD). ALD is one of the most common peroxisomal disorders and is characterized by a defect in degradation of very long chain fatty acids (VLCFA), resulting in accumulation of VLCFA in plasma and tissues. The clinical spectrum of ALD is wide and includes adrenocortical insufficiency, a slowly progressive myelopathy in adulthood, and cerebral demyelination in a subset of male patients. Cerebral demyelination (cerebral ALD) can be treated with hematopoietic cell transplantation (HCT) but only in an early (pre- or early symptomatic) stage and therefore active MRI surveillance is recommended for male patients, both pediatric and adult. Although structural MRI of the brain can detect the presence and extent of cerebral lesions, it does not predict if and when cerebral demyelination will occur. There is a great need for imaging techniques that predict onset of cerebral ALD before lesions appear. Also, imaging markers for severity of myelopathy as surrogate outcome measure in clinical trials would facilitate drug development. New quantitative MRI techniques are promising in that respect. This review focuses on structural and quantitative imaging techniques-including magnetic resonance spectroscopy, diffusion tensor imaging, MR perfusion imaging, magnetization transfer (MT) imaging, neurite orientation dispersion and density imaging (NODDI), and myelin water fraction imaging-used in ALD and their role in clinical practice and research opportunities for the future.
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http://dx.doi.org/10.1055/s-0041-1730937DOI Listing
August 2021

MRI Natural History of the Leukodystrophy Vanishing White Matter.

Radiology 2021 09 29;300(3):671-680. Epub 2021 Jun 29.

From the Department of Child Neurology, Emma Children's Hospital, Amsterdam University Medical Centers, Vrije Universiteit and Amsterdam Neuroscience, De Boelelaan 1117, Amsterdam 1081 HV, the Netherlands (M.D.S., M.L.A., M.S.v.d.K.); Department of Epidemiology and Data Science, Amsterdam University Medical Centers, Amsterdam, the Netherlands (T.v.d.B.); Department of Radiology and Nuclear Medicine, Amsterdam University Medical Center, Vrije Universiteit and Amsterdam Neuroscience, Amsterdam, the Netherlands (F.B., P.J.W.P.); Institutes of Neurology and Health Care Engineering, University College London, London, England (F.B.); and Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University, Amsterdam, the Netherlands (M.S.v.d.K.).

Background In vanishing white matter (VWM), a form of leukodystrophy, earlier onset is associated with faster clinical progression. MRI typically shows rarefaction and cystic destruction of the cerebral white matter. Information on the evolution of VWM according to age at onset is lacking. Purpose To determine whether nature and progression of cerebral white matter abnormalities in VWM differ according to age at onset. Materials and Methods Patients with genetically confirmed VWM were stratified into six groups according to age at onset: younger than 1 year, 1 year to younger than 2 years, 2 years to younger than 4 years, 4 years to younger than 8 years, 8 years to younger than 18 years, and 18 years or older. With institutional review board approval, all available MRI scans obtained between 1985 and 2019 were retrospectively analyzed with three methods: ratio of the width of the lateral ventricles over the skull (ventricle-to-skull ratio [VSR]) was measured to estimate brain atrophy; cerebral white matter was visually scored as percentage normal, hyperintense, rarefied, or cystic on fluid-attenuated inversion recovery (FLAIR) images and converted into a white matter decay score; and the intracranial volume was segmented into normal-appearing white and gray matter, abnormal but structurally present (FLAIR-hyperintense) and rarefied or cystic (FLAIR-hypointense) white matter, and ventricular and extracerebral cerebrospinal fluid (CSF). Multilevel regression analyses with patient as a clustering variable were performed to account for the nested data structure. Results A total of 461 examinations in 270 patients (median age, 7 years [interquartile range, 3-18 years]; 144 female patients) were evaluated; 112 patients had undergone serial imaging. Patients with later onset had higher VSR [F(5) = 8.42; < .001] and CSF volume [F(5) = 21.7; < .001] and lower white matter decay score [F(5) = 4.68; < .001] and rarefied or cystic white matter volume [F(5) = 13.3; < .001]. Rate of progression of white matter decay scores [b = -1.6, t(109) = -3.9; < .001] and VSRs [b = -0.05, t (109) = -3.7; < .001] were lower with later onset. Conclusion A radiologic spectrum based on age at onset exists in vanishing white matter. The earlier the onset, the faster and more cystic the white matter decay, whereas with later onset, white matter atrophy and gliosis predominate. © RSNA, 2021.
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http://dx.doi.org/10.1148/radiol.2021210110DOI Listing
September 2021

Expanding the clinical and radiological phenotypes of leukoencephalopathy due to biallelic HMBS mutations.

Am J Med Genet A 2021 10 4;185(10):2941-2950. Epub 2021 Jun 4.

Murdoch Children's Research Institute, Parkville, Australia.

Pathogenic heterozygous variants in HMBS encoding the enzyme hydroxymethylbilane synthase (HMBS), also known as porphobilinogen deaminase, cause acute intermittent porphyria (AIP). Biallelic variants in HMBS have been reported in a small number of children with severe progressive neurological disease and in three adult siblings with a more slowly, progressive neurological disease and distinct leukoencephalopathy. We report three further adult individuals who share a distinct pattern of white matter abnormality on brain MRI in association with biallelic variants in HMBS, two individuals with homozygous variants, and one with compound-heterozygous variants. We present their clinical and radiological features and compare these with the three adult siblings previously described with leukoencephalopathy and biallelic HMBS variants. All six affected individuals presented with slowly progressive spasticity, ataxia, peripheral neuropathy, with or without mild cognitive impairment, and/or ocular disease with onset in childhood or adolescence. Their brain MRIs show mainly confluent signal abnormalities in the periventricular and deep white matter and bilateral thalami. This recognizable pattern of MRI abnormalities is seen in all six adults described here. Biallelic variants in HMBS cause a phenotype that is distinct from AIP. It is not known whether AIP treatments benefit individuals with HMBS-related leukoencephalopathy. One individual reported here had improved neurological function for 12 months following liver transplantation followed by decline and progression of disease.
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http://dx.doi.org/10.1002/ajmg.a.62377DOI Listing
October 2021

Pathology of the neurovascular unit in leukodystrophies.

Acta Neuropathol Commun 2021 06 3;9(1):103. Epub 2021 Jun 3.

Department of Pathology, Amsterdam UMC, Vrije Universiteit Amsterdam and Amsterdam Neuroscience, de Boelelaan 1117, 1081HV, Amsterdam, The Netherlands.

The blood-brain barrier is a dynamic endothelial cell barrier in the brain microvasculature that separates the blood from the brain parenchyma. Specialized brain endothelial cells, astrocytes, neurons, microglia and pericytes together compose the neurovascular unit and interact to maintain blood-brain barrier function. A disturbed brain barrier function is reported in most common neurological disorders and may play a role in disease pathogenesis. However, a comprehensive overview of how the neurovascular unit is affected in a wide range of rare disorders is lacking. Our aim was to provide further insights into the neuropathology of the neurovascular unit in leukodystrophies to unravel its potential pathogenic role in these diseases. Leukodystrophies are monogenic disorders of the white matter due to defects in any of its structural components. Single leukodystrophies are exceedingly rare, and availability of human tissue is unique. Expression of selective neurovascular unit markers such as claudin-5, zona occludens 1, laminin, PDGFRβ, aquaporin-4 and α-dystroglycan was investigated in eight different leukodystrophies using immunohistochemistry. We observed tight junction rearrangements, indicative of endothelial dysfunction, in five out of eight assessed leukodystrophies of different origin and an altered aquaporin-4 distribution in all. Aquaporin-4 redistribution indicates a general astrocytic dysfunction in leukodystrophies, even in those not directly related to astrocytic pathology or without prominent reactive astrogliosis. These findings provide further evidence for dysfunction in the orchestration of the neurovascular unit in leukodystrophies and contribute to a better understanding of the underlying disease mechanism.
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http://dx.doi.org/10.1186/s40478-021-01206-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8173888PMC
June 2021

LBSL: Case Series and DARS2 Variant Analysis in Early Severe Forms With Unexpected Presentations.

Neurol Genet 2021 Apr 2;7(2):e559. Epub 2021 Feb 2.

Department of Child Neurology, Emma Childrens Hospital, Amsterdam University Medical Centers, Vrije Universiteit and Amsterdam Neuroscience, The Netherlands (M.D.S., T.E.M.A.); Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Italy (S.F., C.D., P.G.); Area di Ricerca Genetica e Malattie Rare (E.B.), Ospedale Pediatrico Bambino Gesù, IRCCS, Rome, Italy; Laboratory of Oncology and Molecular Genetics (K.A.), Clínica las Condes, Santiago, Chile; Department of Pediatric Neurology (C.C.), Clínica Las Condes, Santiago, Chile; Division of Child Neurology (P.T.), Department of Neurology, Istanbul Faculty of Medicine, Turkey; Department of Paediatrics (C.A.S.), Royal Childrens Hospital, Murdoch Childrens Research Institute and University of Melbourne, Victoria, Australia; Pediatric Neurology (C.E.E.), Radboud University Medical Center, Amalia Childrens Hospital, Nijmegen, The Netherlands; Department of Pediatrics (A.S.-V.), University of South Florida, Tampa; Unit of Pediatric Neurology and Neurorehabilitation (S.L.), Department WomanMother-Child, Lausanne University Hospital, Switzerland; Community Pediatrics, Royal Berkshire Hospital, Reading (S.H.), United Kingdom; Neuropediatric Department (T.S.-M.), Childrens Hospital, Luzern, Switzerland; Unit of Neurorehabilitation (G.V.), Department of Neurosciences, Bambino Gesù Children's Research Hospital, IRCCS, Rome, Italy; Paediatric Neurology (G.C.), Nottingham Childrens Hospital, United Kingdom; PEDEGO Research Unit (E.R.), Medical Research Center and Department of Clinical Genetics, University of Oulu and Oulu University Hospital, Finland; Radiology (C.O.), Clínica las Condes, Santiago, Chile; Unit of Neuromuscular and Neurodegenerative Disorders (E.S.B), Area di Ricerca Genetica e Malattie Rare and Department of Neurosciences, Bambino Gesù Children's Research Hospital, IRCCS, Rome, Italy; and Department of Child Neurology (M.S.v.d.K.), Emma Childrens Hospital and Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University, Amsterdam, the Netherlands.

Objective: Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is regarded a relatively mild leukodystrophy, diagnosed by characteristic long tract abnormalities on MRI and biallelic variants in , encoding mitochondrial aspartyl-tRNA synthetase (mtAspRS). variants in LBSL are almost invariably compound heterozygous; in 95% of cases, 1 is a leaky splice site variant in intron 2. A few severely affected patients, still fulfilling the MRI criteria, have been described. We noticed highly unusual MRI presentations in 15 cases diagnosed by WES. We examined these cases to determine whether they represent consistent novel LBSL phenotypes.

Methods: We reviewed clinical features, MRI abnormalities, and gene variants and investigated the variants' impact on mtAspRS structure and mitochondrial function.

Results: We found 2 MRI phenotypes: early severe cerebral hypoplasia/atrophy (9 patients, group 1) and white matter abnormalities without long tract involvement (6 patients, group 2). With antenatal onset, microcephaly, and arrested development, group 1 patients were most severely affected. variants were severer than for classic LBSL and severer for group 1 than group 2. All missense variants hit mtAspRS regions involved in tRNA binding, aspartyl-adenosine-5'-monophosphate binding, and/or homodimerization. Missense variants expressed in the yeast ortholog showed severely affected mitochondrial function.

Conclusions: variants are associated with highly heterogeneous phenotypes. New MRI presentations are profound cerebral hypoplasia/atrophy and white matter abnormalities without long tract involvement. Our findings have implications for diagnosis and understanding disease mechanisms, pointing at dominant neuronal/axonal involvement in severe cases. In line with this conclusion, activation of biallelic null alleles in conditional transgenic mice leads to massive neuronal apoptosis.
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http://dx.doi.org/10.1212/NXG.0000000000000559DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8105885PMC
April 2021

Bi-allelic KARS1 pathogenic variants affecting functions of cytosolic and mitochondrial isoforms are associated with a progressive and multisystem disease.

Hum Mutat 2021 06 11;42(6):745-761. Epub 2021 May 11.

Department of Translational Medicine, Federico II University, Naples, Italy.

KARS1 encodes a lysyl-transfer RNA synthetase (LysRS) that links lysine to its cognate transfer RNA. Two different KARS1 isoforms exert functional effects in cytosol and mitochondria. Bi-allelic pathogenic variants in KARS1 have been associated to sensorineural hearing and visual loss, neuropathy, seizures, and leukodystrophy. We report the clinical, biochemical, and neuroradiological features of nine individuals with KARS1-related disorder carrying 12 different variants with nine of them being novel. The consequences of these variants on the cytosol and/or mitochondrial LysRS were functionally validated in yeast mutants. Most cases presented with severe neurological features including congenital and progressive microcephaly, seizures, developmental delay/intellectual disability, and cerebral atrophy. Oculo-motor dysfunction and immuno-hematological problems were present in six and three cases, respectively. A yeast growth defect of variable severity was detected for most variants on both cytosolic and mitochondrial isoforms. The detrimental effects of two variants on yeast growth were partially rescued by lysine supplementation. Congenital progressive microcephaly, oculo-motor dysfunction, and immuno-hematological problems are emerging phenotypes in KARS1-related disorder. The data in yeast emphasize the role of both mitochondrial and cytosolic isoforms in the pathogenesis of KARS1-related disorder and supports the therapeutic potential of lysine supplementation at least in a subset of patients.
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http://dx.doi.org/10.1002/humu.24210DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8251883PMC
June 2021

Homozygous UBA5 Variant Leads to Hypomyelination with Thalamic Involvement and Axonal Neuropathy.

Neuropediatrics 2021 12 14;52(6):489-494. Epub 2021 Apr 14.

Department of Child Neurology, Amsterdam Leukodystrophy Center, Emma Children's Hospital, Amsterdam UMC, and Amsterdam Neuroscience, Vrije Universiteit, Amsterdam, The Netherlands.

The enzyme ubiquitin-like modifier activating enzyme 5 (UBA5) plays an important role in activating ubiquitin-fold modifier 1 (UFM1) and its associated cascade. is widely expressed and known to facilitate the post-translational modification of proteins. Variants in and are involved in neurodevelopmental disorders with early-onset epileptic encephalopathy as a frequently seen disease manifestation. Using whole exome sequencing, we detected a homozygous variant (c.895C > T p. [Pro299Ser]) in a patient with severe global developmental delay and epilepsy, the latter from the age of 4 years. Magnetic resonance imaging showed hypomyelination with atrophy and T2 hyperintensity of the thalamus. Histology of the sural nerve showed axonal neuropathy with decreased myelin. Functional analyses confirmed the effect of the Pro299Ser variant on UBA5 protein function, showing 58% residual protein activity. Our findings indicate that the epilepsy currently associated with variants may present later in life than previously thought, and that radiological signs include hypomyelination and thalamic involvement. The data also reinforce recently reported associations between variants and peripheral neuropathy.
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http://dx.doi.org/10.1055/s-0041-1724130DOI Listing
December 2021

Fatal perinatal mitochondrial cardiac failure caused by recurrent duplications in the locus.

Med (N Y) 2021 Jan 9;2(1):49-73. Epub 2020 Jul 9.

Genetic Metabolic Disorders Service, Sydney Children's Hospital Network, The Children's Hospital at Westmead, Sydney, NSW 2145, Australia.

Background: In about half of all patients with a suspected monogenic disease, genomic investigations fail to identify the diagnosis. A contributing factor is the difficulty with repetitive regions of the genome, such as those generated by segmental duplications. The locus is one such region, in which recessive deletions and dominant duplications have recently been reported to cause lethal perinatal mitochondrial diseases characterized by pontocerebellar hypoplasia or cardiomyopathy, respectively.

Methods: Whole exome, whole genome and long-read DNA sequencing techniques combined with studies of RNA and quantitative proteomics were used to investigate 17 subjects from 16 unrelated families with suspected mitochondrial disease.

Findings: We report six different duplications in the gene locus causing a distinctive presentation including lethal perinatal cardiomyopathy, persistent hyperlactacidemia, and frequently corneal clouding or cataracts and encephalopathy. The recurrent 68 Kb duplications are identifiable from genome and exome sequencing but usually missed by microarrays. The duplications result in the formation of identical chimeric ATAD3A/ATAD3C proteins, altered ATAD3 complexes and a striking reduction in mitochondrial oxidative phosphorylation complex I and its activity in heart tissue.

Conclusions: duplications appear to act in a dominant-negative manner and the inheritance infers a low recurrence risk for families, unlike most pediatric mitochondrial diseases. More than 350 genes underlie mitochondrial diseases. In our experience the locus is now one of the five most common causes of nuclear-encoded pediatric mitochondrial disease but the repetitive nature of the locus means diagnoses may be frequently missed by current genomic strategies.

Funding: Australian NHMRC, US Department of Defense, Japanese AMED and JSPS agencies, Australian Genomics Health Alliance and Australian Mito Foundation.
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http://dx.doi.org/10.1016/j.medj.2020.06.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7875323PMC
January 2021

Vanishing white matter: Eukaryotic initiation factor 2B model and the impact of missense mutations.

Mol Genet Genomic Med 2021 03 12;9(3):e1593. Epub 2021 Jan 12.

Department of Child Neurology, Emma Children's Hospital, Amsterdam University Medical Centers, Vrije Universiteit and Amsterdam Neuroscience, Amsterdam, the Netherlands.

Background: Vanishing white matter (VWM) is a leukodystrophy, caused by recessive mutations in eukaryotic initiation factor 2B (eIF2B)-subunit genes (EIF2B1-EIF2B5); 80% are missense mutations. Clinical severity is highly variable, with a strong, unexplained genotype-phenotype correlation.

Materials And Methods: With information from a recent natural history study, we severity-graded 97 missense mutations. Using in silico modeling, we created a new human eIF2B model structure, onto which we mapped the missense mutations. Mutated residues were assessed for location in subunits, eIF2B complex, and functional domains, and for information on biochemical activity.

Results: Over 50% of mutations have (ultra-)severe phenotypic effects. About 60% affect the ε-subunit, containing the catalytic domain, mostly with (ultra-)severe effects. About 55% affect subunit cores, with variable clinical severity. About 36% affect subunit interfaces, mostly with severe effects. Very few mutations occur on the external eIf2B surface, perhaps because they have minor functional effects and are tolerated. One external surface mutation affects eIF2B-substrate interaction and is associated with ultra-severe phenotype.

Conclusion: Mutations that lead to (ultra-)severe disease mostly affect amino acids with pivotal roles in complex formation and function of eIF2B. Therapies for VWM are emerging and reliable mutation-based phenotype prediction is required for propensity score matching for trials and in the future for individualized therapy decisions.
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http://dx.doi.org/10.1002/mgg3.1593DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8104162PMC
March 2021

Hypomyelinating leukodystrophies - unravelling myelin biology.

Nat Rev Neurol 2021 Feb 15;17(2):88-103. Epub 2020 Dec 15.

Department of Child Neurology, Amsterdam Leukodystrophy Centre, Emma Children's Hospital, Amsterdam University Medical Centres, Vrije Universiteit, Netherlands.

Hypomyelinating leukodystrophies constitute a subset of genetic white matter disorders characterized by a primary lack of myelin deposition. Most patients with severe hypomyelination present in infancy or early childhood and develop severe neurological deficits, but the clinical presentation can also be mild with onset of symptoms in adolescence or adulthood. MRI can be used to visualize the process of myelination in detail, and MRI pattern recognition can provide a clinical diagnosis in many patients. Next-generation sequencing provides a definitive diagnosis in 80-90% of patients. Genes associated with hypomyelination include those that encode structural myelin proteins but also many that encode proteins involved in RNA translation and some lysosomal proteins. The precise pathomechanisms remain to be elucidated. Improved understanding of the process of myelination, the metabolic axonal support functions of myelin and the proposed contribution of myelin to CNS plasticity provide possible explanations as to why almost all patients with hypomyelination experience slow clinical decline after a long phase of stability. In this Review, we provide an overview of the hypomyelinating leukodystrophies, the advances in our understanding of myelin biology and of the genes involved in these disorders, and the insights these advances have provided into their clinical presentations and evolution.
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http://dx.doi.org/10.1038/s41582-020-00432-1DOI Listing
February 2021

Isocaloric low protein diet in a mouse model for vanishing white matter does not impact ISR deregulation in brain, but reveals ISR deregulation in liver.

Nutr Neurosci 2020 Nov 25:1-12. Epub 2020 Nov 25.

Child Neurology, Emma Children's Hospital, Amsterdam University Medical Centers, Vrije Universiteit and Amsterdam Neuroscience, Amsterdam, the Netherlands.

Vanishing white matter (VWM) is a genetic brain white matter disorder caused by mutations in eIF2B. eIF2B is central in the integrated stress response (ISR), during which its activity is inhibited by various cellular stresses. VWM is a chronic progressive disease with episodes of rapid neurological deterioration provoked by stresses. VWM patients and VWM mouse models show ISR deregulation in brain, correlating with chronic disease development. ISR inhibition ameliorates the chronic disease in VWM mice. The subacute deteriorations have not been modeled yet. We hypothesized that ISR activation could worsen disease progression in mice and model the episodic neurological deterioration. We chose to activate the ISR by subjecting wild-type (wt) and VWM mice to an isocaloric low protein diet. This model would allow us to investigate the contribution of ISR activation in subacute decline in VWM. We found that the low protein diet did not significantly affect amino acid levels nor ISR levels in wt and VWM mouse brain. Our study serendipitously led to the discovery of increased levels of glycine, asparagine and mRNA in VWM mouse brain irrespective of the dietary protein content. Strikingly, the ISR was not activated by the low protein diet in the liver of VWM in contrast to wt mice, due to a modest ISR deregulation in this organ. A model for subacute neurological deterioration in VWM was not established. Possibly, ISR deregulation in VWM results in reduced ISR responsiveness.
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http://dx.doi.org/10.1080/1028415X.2020.1846356DOI Listing
November 2020

Clinical and Functional Consequences of C-Terminal Variants in MCT8: A Case Series.

J Clin Endocrinol Metab 2021 01;106(2):539-553

Academic Center For Thyroid Disease, Department of Internal Medicine, Erasmus Medical Center, GD Rotterdam, The Netherlands.

Context: Genetic variants in SLC16A2, encoding the thyroid hormone transporter MCT8, can cause intellectual and motor disability and abnormal serum thyroid function tests, known as MCT8 deficiency. The C-terminal domain of MCT8 is poorly conserved, which complicates prediction of the deleteriousness of variants in this region. We studied the functional consequences of 5 novel variants within this domain and their relation to the clinical phenotypes.

Methods: We enrolled male subjects with intellectual disability in whom genetic variants were identified in exon 6 of SLC16A2. The impact of identified variants was evaluated in transiently transfected cell lines and patient-derived fibroblasts.

Results: Seven individuals from 5 families harbored potentially deleterious variants affecting the C-terminal domain of MCT8. Two boys with clinical features considered atypical for MCT8 deficiency had a missense variant [c.1724A>G;p.(His575Arg) or c.1796A>G;p.(Asn599Ser)] that did not affect MCT8 function in transfected cells or patient-derived fibroblasts, challenging a causal relationship. Two brothers with classical MCT8 deficiency had a truncating c.1695delT;p.(Val566*) variant that completely inactivated MCT8 in vitro. The 3 other boys had relatively less-severe clinical features and harbored frameshift variants that elongate the MCT8 protein [c.1805delT;p.(Leu602HisfsTer680) and c.del1826-1835;p.(Pro609GlnfsTer676)] and retained ~50% residual activity. Additional truncating variants within transmembrane domain 12 were fully inactivating, whereas those within the intracellular C-terminal tail were tolerated.

Conclusions: Variants affecting the intracellular C-terminal tail of MCT8 are likely benign unless they cause frameshifts that elongate the MCT8 protein. These findings provide clinical guidance in the assessment of the pathogenicity of variants within the C-terminal domain of MCT8.
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http://dx.doi.org/10.1210/clinem/dgaa795DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7823235PMC
January 2021

Endocrine and Growth Abnormalities in 4H Leukodystrophy Caused by Variants in POLR3A, POLR3B, and POLR1C.

J Clin Endocrinol Metab 2021 01;106(2):e660-e674

Department of Child Neurology, University Children's Hospital Tübingen, Tübingen, Germany.

Context: 4H or POLR3-related leukodystrophy is an autosomal recessive disorder typically characterized by hypomyelination, hypodontia, and hypogonadotropic hypogonadism, caused by biallelic pathogenic variants in POLR3A, POLR3B, POLR1C, and POLR3K. The endocrine and growth abnormalities associated with this disorder have not been thoroughly investigated to date.

Objective: To systematically characterize endocrine abnormalities of patients with 4H leukodystrophy.

Design: An international cross-sectional study was performed on 150 patients with genetically confirmed 4H leukodystrophy between 2015 and 2016. Endocrine and growth abnormalities were evaluated, and neurological and other non-neurological features were reviewed. Potential genotype/phenotype associations were also investigated.

Setting: This was a multicenter retrospective study using information collected from 3 predominant centers.

Patients: A total of 150 patients with 4H leukodystrophy and pathogenic variants in POLR3A, POLR3B, or POLR1C were included.

Main Outcome Measures: Variables used to evaluate endocrine and growth abnormalities included pubertal history, hormone levels (estradiol, testosterone, stimulated LH and FSH, stimulated GH, IGF-I, prolactin, ACTH, cortisol, TSH, and T4), and height and head circumference charts.

Results: The most common endocrine abnormalities were delayed puberty (57/74; 77% overall, 64% in males, 89% in females) and short stature (57/93; 61%), when evaluated according to physician assessment. Abnormal thyroid function was reported in 22% (13/59) of patients.

Conclusions: Our results confirm pubertal abnormalities and short stature are the most common endocrine features seen in 4H leukodystrophy. However, we noted that endocrine abnormalities are typically underinvestigated in this patient population. A prospective study is required to formulate evidence-based recommendations for management of the endocrine manifestations of this disorder.
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http://dx.doi.org/10.1210/clinem/dgaa700DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7823228PMC
January 2021

Five men with arresting and relapsing cerebral adrenoleukodystrophy.

J Neurol 2021 Mar 29;268(3):936-940. Epub 2020 Sep 29.

Department of Pediatric Neurology, Lucille-Packard Children's Hospital, Stanford University School of Medicine, Stanford, CA, USA.

Background: X-linked adrenoleukodystrophy (ALD) is the most common genetic peroxisomal disorder with an estimated prevalence of 1:15,000. Approximately two-thirds of males with ALD manifest the inflammatory demyelinating cerebral phenotype (cALD) at some disease stage, in which focal, inflammatory lesions progress over months to years. Hematopoietic stem-cell transplantation can permanently halt cALD progression, but it is only effective if initiated early. Although most cALD lesions progress relentlessly, a subset may spontaneously arrest; subsequent reactivation of these arrested lesions has not been previously detailed.

Objective: We describe a novel arresting-relapsing variant of cALD.

Methods: Salient clinical and radiographic studies were reviewed and summarized for cALD patients with episodic deteriorations.

Results: We report a series of five unrelated men with spontaneously arrested cALD lesions that subsequently manifested signs of clinical and radiologic lesion progression during longitudinal follow-up. In three of five patients, functional status was too poor to attempt transplant by the time the recurrence was identified. One patient experienced reactivation followed by another period of spontaneous arrest.

Conclusions: These cases emphasize the need for continued clinical and radiologic vigilance for adult men with ALD to screen for evidence of new or reactivated cALD lesions to facilitate prompt treatment evaluation.
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http://dx.doi.org/10.1007/s00415-020-10225-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8025682PMC
March 2021

Postural Body Sway as Surrogate Outcome for Myelopathy in Adrenoleukodystrophy.

Front Physiol 2020 17;11:786. Epub 2020 Jul 17.

Department of Pediatric Neurology, Amsterdam Leukodystrophy Center, Emma Children's Hospital, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, Netherlands.

Background: Myelopathy is the core clinical manifestation of adrenoleukodystrophy (ALD), which is the most common peroxisomal disorder. Development of therapies requires sensitive and clinically relevant outcome measures. Together with spastic paraparesis, balance disturbance is the main cause of disability from myelopathy in ALD. In this cross-sectional study, we evaluated whether postural body sway - a measure of balance - could serve as a surrogate outcome in clinical trials.

Methods: Forty-eight male ALD patients and 49 age-matched healthy male controls were included in this study. We compared sway amplitude and sway path of ALD patients to controls. We then correlated the body sway parameters showing the largest between-group differences with clinical measures of severity of myelopathy. To correct for age, we performed multiple linear regression analysis with age and severity of myelopathy as independent variables.

Results: All body sway parameters were significantly higher in patients than in controls, with medium to large effect sizes ( = 0.43-0.66, < 0.001). In the subgroup of asymptomatic patients, body sway amplitude was also higher, but the difference with controls was smaller than for symptomatic patients (effect size = 0.38-0.46). We found moderate to strong correlations between body sway amplitude and clinical severity of myelopathy ( = 0.40-0.79, < 0.005). After correction for age, severity of myelopathy was a significant predictor of body sway amplitude in all regression models.

Conclusions: These results indicate that postural body sway may serve as a surrogate outcome for myelopathy in ALD. Such outcomes are important to evaluate new therapies in clinical trials. Further longitudinal studies are needed and ongoing in this cohort.
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http://dx.doi.org/10.3389/fphys.2020.00786DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7379508PMC
July 2020

Correction to: Berardinelli-Seip syndrome and achalasia: a shared pathomechanism?

Eur J Pediatr 2020 Oct;179(10):1653-1654

Department of Pediatric Gastroenterology, VU University Medical Center, Amsterdam, The Netherlands.

Although the patient has provided consent for publication of this case report and accompanying images, after publication of this article it has come to the authors' attention that Fig. 1 needs changes to better protect the privacy of the patient. A modified Fig. 1 is included in this Erratum. The original Fig. 1 has been removed to protect the patient's privacy.
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http://dx.doi.org/10.1007/s00431-020-03743-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7645574PMC
October 2020

Metachromatic leukodystrophy genotypes in The Netherlands reveal novel pathogenic ARSA variants in non-Caucasian patients.

Neurogenetics 2020 10 7;21(4):289-299. Epub 2020 Jul 7.

Amsterdam Leukodystrophy Center, Department of Child Neurology, Emma Children's Hospital, Amsterdam University Medical Center, VU University Amsterdam and Amsterdam Neuroscience, De Boelelaan, 1117, Amsterdam, The Netherlands.

Metachromatic leukodystrophy (MLD) is an autosomal recessively inherited sulfatide storage disease caused by deficient activity of the lysosomal enzyme arylsulfatase A (ASA). Genetic analysis of the ARSA gene is important in MLD diagnosis and screening of family members. In addition, more information on genotype prevalence will help interpreting MLD population differences between countries. In this study, we identified 31 different ARSA variants in the patient cohort (n = 67) of the Dutch expertise center for MLD. The most frequently found variant, c.1283C > T, p.(Pro428Leu), was present in 43 (64%) patients and resulted in a high prevalence of the juvenile MLD type (58%) in The Netherlands. Furthermore, we observed in five out of six patients with a non-Caucasian ethnic background previously unreported pathogenic ARSA variants. In total, we report ten novel variants including four missense, two nonsense, and two frameshift variants and one in-frame indel, which were all predicted to be disease causing in silico. In addition, one silent variant was found, c.1200C > T, that most likely resulted in erroneous exonic splicing, including partial skipping of exon 7. The c.1200C > T variant was inherited in cis with the pseudodeficiency allele c.1055A > G, p.(Asn352Ser) + ∗96A > G. With this study we provide a genetic base of the unique MLD phenotype distribution in The Netherlands. In addition, our study demonstrated the importance of genetic analysis in MLD diagnosis and the increased likelihood of unreported, pathogenic ARSA variants in patients with non-Caucasian ethnic backgrounds.
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http://dx.doi.org/10.1007/s10048-020-00621-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7476914PMC
October 2020

Disease characteristics of MCT8 deficiency: an international, retrospective, multicentre cohort study.

Lancet Diabetes Endocrinol 2020 07;8(7):594-605

Department of Diabetes and Endocrinology, Women's and Children's Hospital, North Adelaide, SA, Australia.

Background: Disordered thyroid hormone transport, due to mutations in the SLC16A2 gene encoding monocarboxylate transporter 8 (MCT8), is characterised by intellectual and motor disability resulting from cerebral hypothyroidism and chronic peripheral thyrotoxicosis. We sought to systematically assess the phenotypic characteristics and natural history of patients with MCT8 deficiency.

Methods: We did an international, multicentre, cohort study, analysing retrospective data from Jan 1, 2003, to Dec 31, 2019, from patients with MCT8 deficiency followed up in 47 hospitals in 22 countries globally. The key inclusion criterion was genetically confirmed MCT8 deficiency. There were no exclusion criteria. Our primary objective was to analyse the overall survival of patients with MCT8 deficiency and document causes of death. We also compared survival between patients who did or did not attain full head control by age 1·5 years and between patients who were or were not underweight by age 1-3 years (defined as a bodyweight-for-age Z score <-2 SDs or <5th percentile according to WHO definition). Other objectives were to assess neurocognitive function and outcomes, and clinical parameters including anthropometric characteristics, biochemical markers, and neuroimaging findings.

Findings: Between Oct 14, 2014, and Jan 17, 2020, we enrolled 151 patients with 73 different MCT8 (SLC16A2) mutations. Median age at diagnosis was 24·0 months (IQR 12·0-60·0, range 0·0-744·0). 32 (21%) of 151 patients died; the main causes of mortality in these patients were pulmonary infection (six [19%]) and sudden death (six [19%]). Median overall survival was 35·0 years (95% CI 8·3-61·7). Individuals who did not attain head control by age 1·5 years had an increased risk of death compared with patients who did attain head control (hazard ratio [HR] 3·46, 95% CI 1·76-8·34; log-rank test p=0·0041). Patients who were underweight during age 1-3 years had an increased risk for death compared with patients who were of normal bodyweight at this age (HR 4·71, 95% CI 1·26-17·58, p=0·021). The few motor and cognitive abilities of patients did not improve with age, as evidenced by the absence of significant correlations between biological age and scores on the Gross Motor Function Measure-88 and Bayley Scales of Infant Development III. Tri-iodothyronine concentrations were above the age-specific upper limit in 96 (95%) of 101 patients and free thyroxine concentrations were below the age-specific lower limit in 94 (89%) of 106 patients. 59 (71%) of 83 patients were underweight. 25 (53%) of 47 patients had elevated systolic blood pressure above the 90th percentile, 34 (76%) of 45 patients had premature atrial contractions, and 20 (31%) of 64 had resting tachycardia. The most consistent MRI finding was a global delay in myelination, which occurred in 13 (100%) of 13 patients.

Interpretation: Our description of characteristics of MCT8 deficiency in a large patient cohort reveals poor survival with a high prevalence of treatable underlying risk factors, and provides knowledge that might inform clinical management and future evaluation of therapies.

Funding: Netherlands Organisation for Health Research and Development, and the Sherman Foundation.
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http://dx.doi.org/10.1016/S2213-8587(20)30153-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7611932PMC
July 2020

Randomized Clinical Trial of First-Line Genome Sequencing in Pediatric White Matter Disorders.

Ann Neurol 2020 08 9;88(2):264-273. Epub 2020 Jun 9.

Illumina, San Diego, California, USA.

Objective: Genome sequencing (GS) is promising for unsolved leukodystrophies, but its efficacy has not been prospectively studied.

Methods: A prospective time-delayed crossover design trial of GS to assess the efficacy of GS as a first-line diagnostic tool for genetic white matter disorders took place between December 1, 2015 and September 27, 2017. Patients were randomized to receive GS immediately with concurrent standard of care (SoC) testing, or to receive SoC testing for 4 months followed by GS.

Results: Thirty-four individuals were assessed at interim review. The genetic origin of 2 patient's leukoencephalopathy was resolved before randomization. Nine patients were stratified to the immediate intervention group and 23 patients to the delayed-GS arm. The efficacy of GS was significant relative to SoC in the immediate (5/9 [56%] vs 0/9 [0%]; Wild-Seber, p < 0.005) and delayed (control) arms (14/23 [61%] vs 5/23 [22%]; Wild-Seber, p < 0.005). The time to diagnosis was significantly shorter in the immediate-GS group (log-rank test, p = 0.04). The overall diagnostic efficacy of combined GS and SoC approaches was 26 of 34 (76.5%, 95% confidence interval = 58.8-89.3%) in <4 months, greater than historical norms of <50% over 5 years. Owing to loss of clinical equipoise, the trial design was altered to a single-arm observational study.

Interpretation: In this study, first-line GS provided earlier and greater diagnostic efficacy in white matter disorders. We provide an evidence-based diagnostic testing algorithm to enable appropriate clinical GS utilization in this population. ANN NEUROL 2020;88:264-273.
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http://dx.doi.org/10.1002/ana.25757DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8061316PMC
August 2020

Clinical spectrum of POLR3-related leukodystrophy caused by biallelic pathogenic variants.

Neurol Genet 2019 Dec 30;5(6):e369. Epub 2019 Oct 30.

Department of Neurology and Neurosurgery (L.G., L.T.T., K.G., G.B.), McGill University, Montreal, Canada; Department of Pediatrics (L.G., L.T.T., K.G., G.B.), McGill University, Montreal, Canada; Division of Clinical and Metabolic Genetics and Division of Neurology (L.G., G.Y.), The Hospital for Sick Children, University of Toronto, Toronto, Canada; Department of Child Neurology (F.K.C., M.S.V.D.K., N.I.W.), Emma Children's Hospital, Amsterdam University Medical Centers, Vrije Universiteit Amsterdam, and Amsterdam Neuroscience, Amsterdam, The Netherlands; Department of Clinical Genetics (F.K.C., R.M.V.S.), VU University Medical Center, Amsterdam, The Netherlands; Department of Human Genetics (F.K.C.), Center for Biomedical Research, Diponegoro University, Semarang, Indonesia; Department of Pediatrics (L.S.), Faculty of Medicine, University of Szeged, Szeged, Hungary; Child Health and Human Development Program (L.T.T., K.G., G.B.), Research Institute of the McGill University Health Center, Montreal, Canada; Division of Medical Genetics, Department of Specialized Medicine (L.T.T., K.G., G.B.), McGill University Health Center, Montreal, Canada; Centre de Référence Neurogénétique (F.H., C.G.), Service de Génétique, CHU Bordeaux, Bordeaux, France; Department of Pediatrics (E.L.F.), Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China; Developmental Neurology Department (S.D.A.), Fondazione IRCCS Istituto Neurologico C. Besta, Milan, Italy; Neuroscience and Neurorehabilitation Department (G.V.), Bambino Gesu Children's Hospital, Rome, Italy; Center for Pediatric Genomic Medicine (I.T.), Children's Mercy Hospitals and Clinics, Kansas City, MO; University of Missouri-Kansas City School of Medicine (I.T.), Kansas City, MO; Department of Pathology and Laboratory Medicine (I.T.), Children's Mercy Hospitals, Kansas City, MO; Department of Pediatrics (D.M.N.), Section of Medical Genetics, Ochsner for Children, New Orleans, LA; GeneDx (R.P.), Gaithersburg, MD; Division of Neurology (K.S.L.), Barrow Neurological Institute, Phoenix Children's Hospital, Phoenix, AZ; Department of Pediatric Neurology (E.W.), Birmingham Children's Hospital, Birmingham, United Kingdom; Department of Medical Genetics (T.P.), Telemark Hospital, Skien, Norway; Department of Paediatric Neurology (P.F.), St Georges University Hospital NHS Foundation Trust, London, United Kingdom; Clinical Genetics Service (M.M.), St George's University Hospitals NHS Foundation Trust, London, United Kingdom; Clinical Genetics Department (J.R.), Royal Devon and Exeter Hospital NHS Trust, Exeter, United Kingdom; Department of Neurology and Neurosurgery (R.W.), The Children's Hospital at Westmead, Westmead, New South Wales, Australia; Center of Developmental Neurology (H.P.), Frankfurt, Germany; Department of Neurology (B.V.D.W.), Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands; Department of Neurology (D.T.), Essen University Hospital, University of Duisburg-Essen, Essen, Germany; Department of Clinical Genetics (A.D., C.S.), Nottingham University Hospitals NHS Trust, Nottingham, United Kingdom; Wellcome Sanger Institute (DDD Study), Wellcome Genome Campus, Cambridge, United Kingdom; Department of Pediatrics (N.T.), Division of Child Neurology, University of Texas Health Science Center, Houston, TX, United States of America; Movement Disorders Center and Neurogenetics Research Program (M.C.K.), Barrow Neurological Institute, Phoenix Children's Hospital, Phoenix, AZ; Program in Neuroscience (M.C.K.), Arizona State University, Tempe, AZ, United States of America; Division of Neurology (S.S.), Department of Pediatrics, Lady Hardinge Medical College and Associated Kalawati Saran Children's Hospital, New Delhi, India; Division of Neurology (A.V.), Children's Hospital of Philadelphia, Philadelphia, PA; Department of Neurology (A.V.), Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States of America; Department of Child Neurology (D.T.), Neurological Institute C. Besta Foundation IRCCS, Milan, Italy; Department of Functional Genomics (M.S.V.D.K.), VU University, Amsterdam, The Netherlands; Unit of Neuromuscular and Neurodegenerative Disorders (E.B.), Laboratory of Molecular Medicine, Bambino Gesu Children's Hospital, Rome, Italy; Laboratoire MRGM, INSERM U1211, University Bordeaux, Bordeaux, France; Université de Bordeaux (S.F.), INSERM U1212, CNRS 5320, Bordeaux, France; and Department of Human Genetics (G.B.), McGill University, Montreal, Canada.

Objective: To determine the clinical, radiologic, and molecular characteristics of RNA polymerase III-related leukodystrophy (POLR3-HLD) caused by biallelic pathogenic variants.

Methods: A cross-sectional observational study involving 25 centers worldwide was conducted. Clinical and molecular information was collected on 23 unreported and previously reported patients with POLR3-HLD and biallelic pathogenic variants in . Brain MRI studies were reviewed.

Results: Fourteen female and 9 male patients aged 7 days to 23 years were included in the study. Most participants presented early in life (birth to 6 years), and motor deterioration was seen during childhood. A notable proportion of patients required a wheelchair before adolescence, suggesting a more severe phenotype than previously described in POLR3-HLD. Dental, ocular, and endocrine features were not invariably present (70%, 50%, and 50%, respectively). Five patients (22%) had a combination of hypomyelinating leukodystrophy and abnormal craniofacial development, including 1 individual with clear Treacher Collins syndrome (TCS) features. Brain MRI revealed hypomyelination in all cases, often with areas of pronounced T2 hyperintensity corresponding to T1 hypointensity of the white matter. Twenty-nine different pathogenic variants (including 12 new disease-causing variants) in were identified.

Conclusions: This study provides a comprehensive description of POLR3-HLD caused by biallelic pathogenic variants based on the largest cohort of patients to date. These results suggest distinct characteristics of POLR1C-related disorder, with a spectrum of clinical involvement characterized by hypomyelinating leukodystrophy with or without abnormal craniofacial development reminiscent of TCS.
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http://dx.doi.org/10.1212/NXG.0000000000000369DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6927361PMC
December 2019

Metachromatic leukodystrophy and transplantation: remyelination, no cross-correction.

Ann Clin Transl Neurol 2020 02 22;7(2):169-180. Epub 2020 Jan 22.

Department of Child Neurology, Center for Childhood White Matter Diseases, Emma Children's Hospital, Amsterdam University Medical Centers, Vrije Universiteit Amsterdam, and Amsterdam Neuroscience, Amsterdam, The Netherlands.

Objective: In metachromatic leukodystrophy, a lysosomal storage disorder due to decreased arylsulfatase A activity, hematopoietic stem cell transplantation may stop brain demyelination and allow remyelination, thereby halting white matter degeneration. This is the first study to define the effects and therapeutic mechanisms of hematopoietic stem cell transplantation on brain tissue of transplanted metachromatic leukodystrophy patients.

Methods: Autopsy brain tissue was obtained from eight (two transplanted and six nontransplanted) metachromatic leukodystrophy patients, and two age-matched controls. We examined the presence of donor cells by immunohistochemistry and microscopy. In addition, we assessed myelin content, oligodendrocyte numbers, and macrophage phenotypes. An unpaired t-test, linear regression or the nonparametric Mann-Whitney U-test was performed to evaluate differences between the transplanted, nontransplanted, and control group.

Results: In brain tissue of transplanted patients, we found metabolically competent donor macrophages expressing arylsulfatase A distributed throughout the entire white matter. Compared to nontransplanted patients, these macrophages preferentially expressed markers of alternatively activated, anti-inflammatory cells that may support oligodendrocyte survival and differentiation. Additionally, transplanted patients showed higher numbers of oligodendrocytes and evidence for remyelination. Contrary to the current hypothesis on therapeutic mechanism of hematopoietic cell transplantation in metachromatic leukodystrophy, we detected no enzymatic cross-correction to resident astrocytes and oligodendrocytes.

Interpretation: In conclusion, donor macrophages are able to digest accumulated sulfatides and may play a neuroprotective role for resident oligodendrocytes, thereby enabling remyelination, albeit without evidence of cross-correction of oligo- and astroglia. These results emphasize the importance of immunomodulation in addition to the metabolic correction, which might be exploited for improved outcomes.
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http://dx.doi.org/10.1002/acn3.50975DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7034505PMC
February 2020

POLR3A variants with striatal involvement and extrapyramidal movement disorder.

Neurogenetics 2020 04 15;21(2):121-133. Epub 2020 Jan 15.

Department of Child Neurology, Center for Childhood White Matter Diseases, Emma Children's Hospital, Vrije Universiteit, and Amsterdam Neuroscience, Amsterdam University Medical Centers, Amsterdam, The Netherlands.

Biallelic variants in POLR3A cause 4H leukodystrophy, characterized by hypomyelination in combination with cerebellar and pyramidal signs and variable non-neurological manifestations. Basal ganglia are spared in 4H leukodystrophy, and dystonia is not prominent. Three patients with variants in POLR3A, an atypical presentation with dystonia, and MR involvement of putamen and caudate nucleus (striatum) and red nucleus have previously been reported. Genetic, clinical findings and 18 MRI scans from nine patients with homozygous or compound heterozygous POLR3A variants and predominant striatal changes were retrospectively reviewed in order to characterize the striatal variant of POLR3A-associated disease. Prominent extrapyramidal involvement was the predominant clinical sign in all patients. The three youngest children were severely affected with muscle hypotonia, impaired head control, and choreic movements. Presentation of the six older patients was milder. Two brothers diagnosed with juvenile parkinsonism were homozygous for the c.1771-6C > G variant in POLR3A; the other seven either carried c.1771-6C > G (n = 1) or c.1771-7C > G (n = 7) together with another variant (missense, synonymous, or intronic). Striatal T2-hyperintensity and atrophy together with involvement of the superior cerebellar peduncles were characteristic. Additional MRI findings were involvement of dentate nuclei, hila, or peridentate white matter (3, 6, and 4/9), inferior cerebellar peduncles (6/9), red nuclei (2/9), and abnormal myelination of pyramidal and visual tracts (6/9) but no frank hypomyelination. Clinical and MRI findings in patients with a striatal variant of POLR3A-related disease are distinct from 4H leukodystrophy and associated with one of two intronic variants, c.1771-6C > G or c.1771-7C > G, in combination with another POLR3A variant.
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http://dx.doi.org/10.1007/s10048-019-00602-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7064625PMC
April 2020

Genome sequencing in persistently unsolved white matter disorders.

Ann Clin Transl Neurol 2020 01 7;7(1):144-152. Epub 2020 Jan 7.

Division of Neurology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania.

Genetic white matter disorders have heterogeneous etiologies and overlapping clinical presentations. We performed a study of the diagnostic efficacy of genome sequencing in 41 unsolved cases with prior exome sequencing, resolving an additional 14 from an historical cohort (n = 191). Reanalysis in the context of novel disease-associated genes and improved variant curation and annotation resolved 64% of cases. The remaining diagnoses were directly attributable to genome sequencing, including cases with small and large copy number variants (CNVs) and variants in deep intronic and technically difficult regions. Genome sequencing, in combination with other methodologies, achieved a diagnostic yield of 85% in this retrospective cohort.
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http://dx.doi.org/10.1002/acn3.50957DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6952322PMC
January 2020
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