Publications by authors named "Margot R F Reijnders"

26 Publications

  • Page 1 of 1

Germline AGO2 mutations impair RNA interference and human neurological development.

Nat Commun 2020 11 16;11(1):5797. Epub 2020 Nov 16.

Department of Genetics, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada.

ARGONAUTE-2 and associated miRNAs form the RNA-induced silencing complex (RISC), which targets mRNAs for translational silencing and degradation as part of the RNA interference pathway. Despite the essential nature of this process for cellular function, there is little information on the role of RISC components in human development and organ function. We identify 13 heterozygous mutations in AGO2 in 21 patients affected by disturbances in neurological development. Each of the identified single amino acid mutations result in impaired shRNA-mediated silencing. We observe either impaired RISC formation or increased binding of AGO2 to mRNA targets as mutation specific functional consequences. The latter is supported by decreased phosphorylation of a C-terminal serine cluster involved in mRNA target release, increased formation of dendritic P-bodies in neurons and global transcriptome alterations in patient-derived primary fibroblasts. Our data emphasize the importance of gene expression regulation through the dynamic AGO2-RNA association for human neuronal development.
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http://dx.doi.org/10.1038/s41467-020-19572-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7670403PMC
November 2020

Evidence for 28 genetic disorders discovered by combining healthcare and research data.

Nature 2020 10 14;586(7831):757-762. Epub 2020 Oct 14.

Human Genetics Programme, Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, UK.

De novo mutations in protein-coding genes are a well-established cause of developmental disorders. However, genes known to be associated with developmental disorders account for only a minority of the observed excess of such de novo mutations. Here, to identify previously undescribed genes associated with developmental disorders, we integrate healthcare and research exome-sequence data from 31,058 parent-offspring trios of individuals with developmental disorders, and develop a simulation-based statistical test to identify gene-specific enrichment of de novo mutations. We identified 285 genes that were significantly associated with developmental disorders, including 28 that had not previously been robustly associated with developmental disorders. Although we detected more genes associated with developmental disorders, much of the excess of de novo mutations in protein-coding genes remains unaccounted for. Modelling suggests that more than 1,000 genes associated with developmental disorders have not yet been described, many of which are likely to be less penetrant than the currently known genes. Research access to clinical diagnostic datasets will be critical for completing the map of genes associated with developmental disorders.
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http://dx.doi.org/10.1038/s41586-020-2832-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116826PMC
October 2020

Phenotypic spectrum and transcriptomic profile associated with germline variants in TRAF7.

Genet Med 2020 07 7;22(7):1215-1226. Epub 2020 May 7.

Department of Medical Genetics, Lyon Hospices Civils, Lyon, France.

Purpose: Somatic variants in tumor necrosis factor receptor-associated factor 7 (TRAF7) cause meningioma, while germline variants have recently been identified in seven patients with developmental delay and cardiac, facial, and digital anomalies. We aimed to define the clinical and mutational spectrum associated with TRAF7 germline variants in a large series of patients, and to determine the molecular effects of the variants through transcriptomic analysis of patient fibroblasts.

Methods: We performed exome, targeted capture, and Sanger sequencing of patients with undiagnosed developmental disorders, in multiple independent diagnostic or research centers. Phenotypic and mutational comparisons were facilitated through data exchange platforms. Whole-transcriptome sequencing was performed on RNA from patient- and control-derived fibroblasts.

Results: We identified heterozygous missense variants in TRAF7 as the cause of a developmental delay-malformation syndrome in 45 patients. Major features include a recognizable facial gestalt (characterized in particular by blepharophimosis), short neck, pectus carinatum, digital deviations, and patent ductus arteriosus. Almost all variants occur in the WD40 repeats and most are recurrent. Several differentially expressed genes were identified in patient fibroblasts.

Conclusion: We provide the first large-scale analysis of the clinical and mutational spectrum associated with the TRAF7 developmental syndrome, and we shed light on its molecular etiology through transcriptome studies.
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http://dx.doi.org/10.1038/s41436-020-0792-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8093014PMC
July 2020

Characterization of SETD1A haploinsufficiency in humans and Drosophila defines a novel neurodevelopmental syndrome.

Mol Psychiatry 2021 06 28;26(6):2013-2024. Epub 2020 Apr 28.

Center for Pediatric Genomic Medicine, Children's Mercy Hospital, University of Missouri-Kansas City School of Medicine, Kansas City, MO, USA.

Defects in histone methyltransferases (HMTs) are major contributing factors in neurodevelopmental disorders (NDDs). Heterozygous variants of SETD1A involved in histone H3 lysine 4 (H3K4) methylation were previously identified in individuals with schizophrenia. Here, we define the clinical features of the Mendelian syndrome associated with haploinsufficiency of SETD1A by investigating 15 predominantly pediatric individuals who all have de novo SETD1A variants. These individuals present with a core set of symptoms comprising global developmental delay and/or intellectual disability, subtle facial dysmorphisms, behavioral and psychiatric problems. We examined cellular phenotypes in three patient-derived lymphoblastoid cell lines with three variants: p.Gly535Alafs*12, c.4582-2_4582delAG, and p.Tyr1499Asp. These patient cell lines displayed DNA damage repair defects that were comparable to previously observed RNAi-mediated depletion of SETD1A. This suggested that these variants, including the p.Tyr1499Asp in the catalytic SET domain, behave as loss-of-function (LoF) alleles. Previous studies demonstrated a role for SETD1A in cell cycle control and differentiation. However, individuals with SETD1A variants do not show major structural brain defects or severe microcephaly, suggesting that defective proliferation and differentiation of neural progenitors is unlikely the single underlying cause of the disorder. We show here that the Drosophila melanogaster SETD1A orthologue is required in postmitotic neurons of the fly brain for normal memory, suggesting a role in post development neuronal function. Together, this study defines a neurodevelopmental disorder caused by dominant de novo LoF variants in SETD1A and further supports a role for H3K4 methyltransferases in the regulation of neuronal processes underlying normal cognitive functioning.
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http://dx.doi.org/10.1038/s41380-020-0725-5DOI Listing
June 2021

Partial Loss of USP9X Function Leads to a Male Neurodevelopmental and Behavioral Disorder Converging on Transforming Growth Factor β Signaling.

Biol Psychiatry 2020 01 29;87(2):100-112. Epub 2019 Jun 29.

Institute of Human Genetics, Heidelberg University, Heidelberg, Germany.

Background: The X-chromosome gene USP9X encodes a deubiquitylating enzyme that has been associated with neurodevelopmental disorders primarily in female subjects. USP9X escapes X inactivation, and in female subjects de novo heterozygous copy number loss or truncating mutations cause haploinsufficiency culminating in a recognizable syndrome with intellectual disability and signature brain and congenital abnormalities. In contrast, the involvement of USP9X in male neurodevelopmental disorders remains tentative.

Methods: We used clinically recommended guidelines to collect and interrogate the pathogenicity of 44 USP9X variants associated with neurodevelopmental disorders in males. Functional studies in patient-derived cell lines and mice were used to determine mechanisms of pathology.

Results: Twelve missense variants showed strong evidence of pathogenicity. We define a characteristic phenotype of the central nervous system (white matter disturbances, thin corpus callosum, and widened ventricles); global delay with significant alteration of speech, language, and behavior; hypotonia; joint hypermobility; visual system defects; and other common congenital and dysmorphic features. Comparison of in silico and phenotypical features align additional variants of unknown significance with likely pathogenicity. In support of partial loss-of-function mechanisms, using patient-derived cell lines, we show loss of only specific USP9X substrates that regulate neurodevelopmental signaling pathways and a united defect in transforming growth factor β signaling. In addition, we find correlates of the male phenotype in Usp9x brain-specific knockout mice, and further resolve loss of hippocampal-dependent learning and memory.

Conclusions: Our data demonstrate the involvement of USP9X variants in a distinctive neurodevelopmental and behavioral syndrome in male subjects and identify plausible mechanisms of pathogenesis centered on disrupted transforming growth factor β signaling and hippocampal function.
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http://dx.doi.org/10.1016/j.biopsych.2019.05.028DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6925349PMC
January 2020

Enabling Global Clinical Collaborations on Identifiable Patient Data: The Minerva Initiative.

Front Genet 2019 29;10:611. Epub 2019 Jul 29.

Department of Medical Genetics, University of Antwerp, Antwerp, Belgium.

The clinical utility of computational phenotyping for both genetic and rare diseases is increasingly appreciated; however, its true potential is yet to be fully realized. Alongside the growing clinical and research availability of sequencing technologies, precise deep and scalable phenotyping is required to serve unmet need in genetic and rare diseases. To improve the lives of individuals affected with rare diseases through deep phenotyping, global big data interrogation is necessary to aid our understanding of disease biology, assist diagnosis, and develop targeted treatment strategies. This includes the application of cutting-edge machine learning methods to image data. As with most digital tools employed in health care, there are ethical and data governance challenges associated with using identifiable personal image data. There are also risks with failing to deliver on the patient benefits of these new technologies, the biggest of which is posed by data siloing. The Minerva Initiative has been designed to enable the public good of deep phenotyping while mitigating these ethical risks. Its open structure, enabling collaboration and data sharing between individuals, clinicians, researchers and private enterprise, is key for delivering precision public health.
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http://dx.doi.org/10.3389/fgene.2019.00611DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6681681PMC
July 2019

De Novo and Inherited Pathogenic Variants in KDM3B Cause Intellectual Disability, Short Stature, and Facial Dysmorphism.

Am J Hum Genet 2019 04 28;104(4):758-766. Epub 2019 Mar 28.

Department of Human Genetics, Radboud University Medical Center, 6525GA Nijmegen, the Netherlands; Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen, 6525GA Nijmegen, the Netherlands; Department of Clinical Genetics and School for Oncology & Developmental Biology (GROW), Maastricht University Medical Center, 6202AZ Maastricht, the Netherlands.

By using exome sequencing and a gene matching approach, we identified de novo and inherited pathogenic variants in KDM3B in 14 unrelated individuals and three affected parents with varying degrees of intellectual disability (ID) or developmental delay (DD) and short stature. The individuals share additional phenotypic features that include feeding difficulties in infancy, joint hypermobility, and characteristic facial features such as a wide mouth, a pointed chin, long ears, and a low columella. Notably, two individuals developed cancer, acute myeloid leukemia and Hodgkin lymphoma, in childhood. KDM3B encodes for a histone demethylase and is involved in H3K9 demethylation, a crucial part of chromatin modification required for transcriptional regulation. We identified missense and truncating variants, suggesting that KDM3B haploinsufficiency is the underlying mechanism for this syndrome. By using a hybrid facial-recognition model, we show that individuals with a pathogenic variant in KDM3B have a facial gestalt, and that they show significant facial similarity compared to control individuals with ID. In conclusion, pathogenic variants in KDM3B cause a syndrome characterized by ID, short stature, and facial dysmorphism.
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http://dx.doi.org/10.1016/j.ajhg.2019.02.023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6451728PMC
April 2019

De Novo and Inherited Loss-of-Function Variants in TLK2: Clinical and Genotype-Phenotype Evaluation of a Distinct Neurodevelopmental Disorder.

Am J Hum Genet 2018 06 31;102(6):1195-1203. Epub 2018 May 31.

Division of Clinical Genomics, Ambry Genetics, Aliso Viejo, CA 92656, USA.

Next-generation sequencing is a powerful tool for the discovery of genes related to neurodevelopmental disorders (NDDs). Here, we report the identification of a distinct syndrome due to de novo or inherited heterozygous mutations in Tousled-like kinase 2 (TLK2) in 38 unrelated individuals and two affected mothers, using whole-exome and whole-genome sequencing technologies, matchmaker databases, and international collaborations. Affected individuals had a consistent phenotype, characterized by mild-borderline neurodevelopmental delay (86%), behavioral disorders (68%), severe gastro-intestinal problems (63%), and facial dysmorphism including blepharophimosis (82%), telecanthus (74%), prominent nasal bridge (68%), broad nasal tip (66%), thin vermilion of the upper lip (62%), and upslanting palpebral fissures (55%). Analysis of cell lines from three affected individuals showed that mutations act through a loss-of-function mechanism in at least two case subjects. Genotype-phenotype analysis and comparison of computationally modeled faces showed that phenotypes of these and other individuals with loss-of-function variants significantly overlapped with phenotypes of individuals with other variant types (missense and C-terminal truncating). This suggests that haploinsufficiency of TLK2 is the most likely underlying disease mechanism, leading to a consistent neurodevelopmental phenotype. This work illustrates the power of international data sharing, by the identification of 40 individuals from 26 different centers in 7 different countries, allowing the identification, clinical delineation, and genotype-phenotype evaluation of a distinct NDD caused by mutations in TLK2.
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http://dx.doi.org/10.1016/j.ajhg.2018.04.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5992133PMC
June 2018

A Recurrent De Novo PACS2 Heterozygous Missense Variant Causes Neonatal-Onset Developmental Epileptic Encephalopathy, Facial Dysmorphism, and Cerebellar Dysgenesis.

Am J Hum Genet 2018 05 12;102(5):995-1007. Epub 2018 Apr 12.

University of Groningen, University Medical Center Groningen, Department of Genetics, 9700 RB Groningen, the Netherlands.

Developmental and epileptic encephalopathies (DEEs) represent a large clinical and genetic heterogeneous group of neurodevelopmental diseases. The identification of pathogenic genetic variants in DEEs remains crucial for deciphering this complex group and for accurately caring for affected individuals (clinical diagnosis, genetic counseling, impacting medical, precision therapy, clinical trials, etc.). Whole-exome sequencing and intensive data sharing identified a recurrent de novo PACS2 heterozygous missense variant in 14 unrelated individuals. Their phenotype was characterized by epilepsy, global developmental delay with or without autism, common cerebellar dysgenesis, and facial dysmorphism. Mixed focal and generalized epilepsy occurred in the neonatal period, controlled with difficulty in the first year, but many improved in early childhood. PACS2 is an important PACS1 paralog and encodes a multifunctional sorting protein involved in nuclear gene expression and pathway traffic regulation. Both proteins harbor cargo(furin)-binding regions (FBRs) that bind cargo proteins, sorting adaptors, and cellular kinase. Compared to the defined PACS1 recurrent variant series, individuals with PACS2 variant have more consistently neonatal/early-infantile-onset epilepsy that can be challenging to control. Cerebellar abnormalities may be similar but PACS2 individuals exhibit a pattern of clear dysgenesis ranging from mild to severe. Functional studies demonstrated that the PACS2 recurrent variant reduces the ability of the predicted autoregulatory domain to modulate the interaction between the PACS2 FBR and client proteins, which may disturb cellular function. These findings support the causality of this recurrent de novo PACS2 heterozygous missense in DEEs with facial dysmorphim and cerebellar dysgenesis.
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http://dx.doi.org/10.1016/j.ajhg.2018.03.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5986694PMC
May 2018

Expanding the neurodevelopmental phenotype of PURA syndrome.

Am J Med Genet A 2018 01 17;176(1):56-67. Epub 2017 Nov 17.

Department of Neurology, University of Rochester Medical Center, Rochester, New York.

PURA syndrome is a recently described developmental encephalopathy presenting with neonatal hypotonia, feeding difficulties, global developmental delay, severe intellectual disability, and frequent apnea and epilepsy. We describe 18 new individuals with heterozygous sequence variations in PURA. A neuromotor disorder starting with neonatal hyptonia, but ultimately allowing delayed progression to walking, was present in nearly all individuals. Congenital apnea was present in 56% during infancy, but all cases in this cohort resolved during the first year of life. Feeding difficulties were frequently reported, with gastrostomy tube placement required in 28%. Epilepsy was present in 50% of the subjects, including infantile spasms and Lennox-Gastaut syndrome. Skeletal complications were found in 39%. Disorders of gastrointestinal motility and nystagmus were also recurrent features. Autism was diagnosed in one individual, potentially expanding the neurodevelopmental phenotype associated with this syndrome. However, we did not find additional PURA sequence variations in a cohort of 120 subjects with autism. We also present the first neuropathologic studies of PURA syndrome, and describe chronic inflammatory changes around the arterioles within the deep white matter. We did not find significant correlations between mutational class and severity, nor between location of the sequence variation in PUR repeat domains. Further studies are required in larger cohorts of subjects with PURA syndrome to clarify these genotype-phenotype associations.
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http://dx.doi.org/10.1002/ajmg.a.38521DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5821266PMC
January 2018

Recurrent De Novo Mutations Disturbing the GTP/GDP Binding Pocket of RAB11B Cause Intellectual Disability and a Distinctive Brain Phenotype.

Am J Hum Genet 2017 Nov 26;101(5):824-832. Epub 2017 Oct 26.

Department of Human Genetics, and Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, 6500 HB, the Netherlands. Electronic address:

The Rab GTPase family comprises ∼70 GTP-binding proteins, functioning in vesicle formation, transport and fusion. They are activated by a conformational change induced by GTP-binding, allowing interactions with downstream effectors. Here, we report five individuals with two recurrent de novo missense mutations in RAB11B; c.64G>A; p.Val22Met in three individuals and c.202G>A; p.Ala68Thr in two individuals. An overlapping neurodevelopmental phenotype, including severe intellectual disability with absent speech, epilepsy, and hypotonia was observed in all affected individuals. Additionally, visual problems, musculoskeletal abnormalities, and microcephaly were present in the majority of cases. Re-evaluation of brain MRI images of four individuals showed a shared distinct brain phenotype, consisting of abnormal white matter (severely decreased volume and abnormal signal), thin corpus callosum, cerebellar vermis hypoplasia, optic nerve hypoplasia and mild ventriculomegaly. To compare the effects of both variants with known inactive GDP- and active GTP-bound RAB11B mutants, we modeled the variants on the three-dimensional protein structure and performed subcellular localization studies. We predicted that both variants alter the GTP/GDP binding pocket and show that they both have localization patterns similar to inactive RAB11B. Evaluation of their influence on the affinity of RAB11B to a series of binary interactors, both effectors and guanine nucleotide exchange factors (GEFs), showed induction of RAB11B binding to the GEF SH3BP5, again similar to inactive RAB11B. In conclusion, we report two recurrent dominant mutations in RAB11B leading to a neurodevelopmental syndrome, likely caused by altered GDP/GTP binding that inactivate the protein and induce GEF binding and protein mislocalization.
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http://dx.doi.org/10.1016/j.ajhg.2017.09.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5673605PMC
November 2017

De Novo Missense Mutations in DHX30 Impair Global Translation and Cause a Neurodevelopmental Disorder.

Am J Hum Genet 2017 Nov;101(5):716-724

Department of Pediatric Neurology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, the Netherlands.

DHX30 is a member of the family of DExH-box helicases, which use ATP hydrolysis to unwind RNA secondary structures. Here we identified six different de novo missense mutations in DHX30 in twelve unrelated individuals affected by global developmental delay (GDD), intellectual disability (ID), severe speech impairment and gait abnormalities. While four mutations are recurrent, two are unique with one affecting the codon of one recurrent mutation. All amino acid changes are located within highly conserved helicase motifs and were found to either impair ATPase activity or RNA recognition in different in vitro assays. Moreover, protein variants exhibit an increased propensity to trigger stress granule (SG) formation resulting in global translation inhibition. Thus, our findings highlight the prominent role of translation control in development and function of the central nervous system and also provide molecular insight into how DHX30 dysfunction might cause a neurodevelopmental disorder.
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http://dx.doi.org/10.1016/j.ajhg.2017.09.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5673606PMC
November 2017

PURA syndrome: clinical delineation and genotype-phenotype study in 32 individuals with review of published literature.

J Med Genet 2018 02 2;55(2):104-113. Epub 2017 Nov 2.

Department of Pediatric Neurology, Children's Hospital of Pittsburgh of UPMC, Pittsburgh, Pennsylvania, USA.

Background: De novo mutations in have recently been described to cause PURA syndrome, a neurodevelopmental disorder characterised by severe intellectual disability (ID), epilepsy, feeding difficulties and neonatal hypotonia.

Objectives: To delineate the clinical spectrum of PURA syndrome and study genotype-phenotype correlations.

Methods: Diagnostic or research-based exome or Sanger sequencing was performed in individuals with ID. We systematically collected clinical and mutation data on newly ascertained PURA syndrome individuals, evaluated data of previously reported individuals and performed a computational analysis of photographs. We classified mutations based on predicted effect using 3D in silico models of crystal structures of -derived Pur-alpha homologues. Finally, we explored genotype-phenotype correlations by analysis of both recurrent mutations as well as mutation classes.

Results: We report mutations in (purine-rich element binding protein A) in 32 individuals, the largest cohort described so far. Evaluation of clinical data, including 22 previously published cases, revealed that all have moderate to severe ID and neonatal-onset symptoms, including hypotonia (96%), respiratory problems (57%), feeding difficulties (77%), exaggerated startle response (44%), hypersomnolence (66%) and hypothermia (35%). Epilepsy (54%) and gastrointestinal (69%), ophthalmological (51%) and endocrine problems (42%) were observed frequently. Computational analysis of facial photographs showed subtle facial dysmorphism. No strong genotype-phenotype correlation was identified by subgrouping mutations into functional classes.

Conclusion: We delineate the clinical spectrum of PURA syndrome with the identification of 32 additional individuals. The identification of one individual through targeted Sanger sequencing points towards the clinical recognisability of the syndrome. Genotype-phenotype analysis showed no significant correlation between mutation classes and disease severity.
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http://dx.doi.org/10.1136/jmedgenet-2017-104946DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5800346PMC
February 2018

Functional convergence of histone methyltransferases EHMT1 and KMT2C involved in intellectual disability and autism spectrum disorder.

PLoS Genet 2017 Oct 25;13(10):e1006864. Epub 2017 Oct 25.

Department of Biology, Faculty of Science, Western University, London, Ontario, Canada.

Kleefstra syndrome, caused by haploinsufficiency of euchromatin histone methyltransferase 1 (EHMT1), is characterized by intellectual disability (ID), autism spectrum disorder (ASD), characteristic facial dysmorphisms, and other variable clinical features. In addition to EHMT1 mutations, de novo variants were reported in four additional genes (MBD5, SMARCB1, NR1I3, and KMT2C), in single individuals with clinical characteristics overlapping Kleefstra syndrome. Here, we present a novel cohort of five patients with de novo loss of function mutations affecting the histone methyltransferase KMT2C. Our clinical data delineates the KMT2C phenotypic spectrum and reinforces the phenotypic overlap with Kleefstra syndrome and other related ID disorders. To elucidate the common molecular basis of the neuropathology associated with mutations in KMT2C and EHMT1, we characterized the role of the Drosophila KMT2C ortholog, trithorax related (trr), in the nervous system. Similar to the Drosophila EHMT1 ortholog, G9a, trr is required in the mushroom body for short term memory. Trr ChIP-seq identified 3371 binding sites, mainly in the promoter of genes involved in neuronal processes. Transcriptional profiling of pan-neuronal trr knockdown and G9a null mutant fly heads identified 613 and 1123 misregulated genes, respectively. These gene sets show a significant overlap and are associated with nearly identical gene ontology enrichments. The majority of the observed biological convergence is derived from predicted indirect target genes. However, trr and G9a also have common direct targets, including the Drosophila ortholog of Arc (Arc1), a key regulator of synaptic plasticity. Our data highlight the clinical and molecular convergence between the KMT2 and EHMT protein families, which may contribute to a molecular network underlying a larger group of ID/ASD-related disorders.
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http://dx.doi.org/10.1371/journal.pgen.1006864DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5656305PMC
October 2017

RAC1 Missense Mutations in Developmental Disorders with Diverse Phenotypes.

Am J Hum Genet 2017 Sep;101(3):466-477

Manchester Centre for Genomic Medicine, St. Mary's Hospital, Central Manchester NHS Foundation Trust, Manchester Academic Health Sciences Centre, Manchester M13 9WL, UK; Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PL, UK. Electronic address:

RAC1 is a widely studied Rho GTPase, a class of molecules that modulate numerous cellular functions essential for normal development. RAC1 is highly conserved across species and is under strict mutational constraint. We report seven individuals with distinct de novo missense RAC1 mutations and varying degrees of developmental delay, brain malformations, and additional phenotypes. Four individuals, each harboring one of c.53G>A (p.Cys18Tyr), c.116A>G (p.Asn39Ser), c.218C>T (p.Pro73Leu), and c.470G>A (p.Cys157Tyr) variants, were microcephalic, with head circumferences between -2.5 to -5 SD. In contrast, two individuals with c.151G>A (p.Val51Met) and c.151G>C (p.Val51Leu) alleles were macrocephalic with head circumferences of +4.16 and +4.5 SD. One individual harboring a c.190T>G (p.Tyr64Asp) allele had head circumference in the normal range. Collectively, we observed an extraordinary spread of ∼10 SD of head circumferences orchestrated by distinct mutations in the same gene. In silico modeling, mouse fibroblasts spreading assays, and in vivo overexpression assays using zebrafish as a surrogate model demonstrated that the p.Cys18Tyr and p.Asn39Ser RAC1 variants function as dominant-negative alleles and result in microcephaly, reduced neuronal proliferation, and cerebellar abnormalities in vivo. Conversely, the p.Tyr64Asp substitution is constitutively active. The remaining mutations are probably weakly dominant negative or their effects are context dependent. These findings highlight the importance of RAC1 in neuronal development. Along with TRIO and HACE1, a sub-category of rare developmental disorders is emerging with RAC1 as the central player. We show that ultra-rare disorders caused by private, non-recurrent missense mutations that result in varying phenotypes are challenging to dissect, but can be delineated through focused international collaboration.
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http://dx.doi.org/10.1016/j.ajhg.2017.08.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5591022PMC
September 2017

De Novo Mutations in SON Disrupt RNA Splicing of Genes Essential for Brain Development and Metabolism, Causing an Intellectual-Disability Syndrome.

Am J Hum Genet 2016 09 18;99(3):711-719. Epub 2016 Aug 18.

Division of Genetics, Department of Pediatrics, San Antonio Military Medical Center, Fort Sam Houston, TX 78234, USA; Department of Pediatrics, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.

The overall understanding of the molecular etiologies of intellectual disability (ID) and developmental delay (DD) is increasing as next-generation sequencing technologies identify genetic variants in individuals with such disorders. However, detailed analyses conclusively confirming these variants, as well as the underlying molecular mechanisms explaining the diseases, are often lacking. Here, we report on an ID syndrome caused by de novo heterozygous loss-of-function (LoF) mutations in SON. The syndrome is characterized by ID and/or DD, malformations of the cerebral cortex, epilepsy, vision problems, musculoskeletal abnormalities, and congenital malformations. Knockdown of son in zebrafish resulted in severe malformation of the spine, brain, and eyes. Importantly, analyses of RNA from affected individuals revealed that genes critical for neuronal migration and cortex organization (TUBG1, FLNA, PNKP, WDR62, PSMD3, and HDAC6) and metabolism (PCK2, PFKL, IDH2, ACY1, and ADA) are significantly downregulated because of the accumulation of mis-spliced transcripts resulting from erroneous SON-mediated RNA splicing. Our data highlight SON as a master regulator governing neurodevelopment and demonstrate the importance of SON-mediated RNA splicing in human development.
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http://dx.doi.org/10.1016/j.ajhg.2016.06.029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5011044PMC
September 2016

Meta-analysis of 2,104 trios provides support for 10 new genes for intellectual disability.

Nat Neurosci 2016 09 1;19(9):1194-6. Epub 2016 Aug 1.

Department of Human Genetics, Donders Centre for Neuroscience, Radboud University Medical Center, Nijmegen, the Netherlands.

To identify candidate genes for intellectual disability, we performed a meta-analysis on 2,637 de novo mutations, identified from the exomes of 2,104 patient-parent trios. Statistical analyses identified 10 new candidate ID genes: DLG4, PPM1D, RAC1, SMAD6, SON, SOX5, SYNCRIP, TCF20, TLK2 and TRIP12. In addition, we show that these genes are intolerant to nonsynonymous variation and that mutations in these genes are associated with specific clinical ID phenotypes.
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http://dx.doi.org/10.1038/nn.4352DOI Listing
September 2016

De Novo Loss-of-Function Mutations in USP9X Cause a Female-Specific Recognizable Syndrome with Developmental Delay and Congenital Malformations.

Am J Hum Genet 2016 Feb 28;98(2):373-81. Epub 2016 Jan 28.

Institute of Medical Biology, A(∗)STAR, 138648 Singapore, Singapore; Amsterdam Reproduction & Development, Academic Medical Centre & VU University Medical Center, Reproductive Biology Laboratory (Q3-119), Meibergdreef 9, 1105 AZ Amsterdam, the Netherlands.

Mutations in more than a hundred genes have been reported to cause X-linked recessive intellectual disability (ID) mainly in males. In contrast, the number of identified X-linked genes in which de novo mutations specifically cause ID in females is limited. Here, we report 17 females with de novo loss-of-function mutations in USP9X, encoding a highly conserved deubiquitinating enzyme. The females in our study have a specific phenotype that includes ID/developmental delay (DD), characteristic facial features, short stature, and distinct congenital malformations comprising choanal atresia, anal abnormalities, post-axial polydactyly, heart defects, hypomastia, cleft palate/bifid uvula, progressive scoliosis, and structural brain abnormalities. Four females from our cohort were identified by targeted genetic testing because their phenotype was suggestive for USP9X mutations. In several females, pigment changes along Blaschko lines and body asymmetry were observed, which is probably related to differential (escape from) X-inactivation between tissues. Expression studies on both mRNA and protein level in affected-female-derived fibroblasts showed significant reduction of USP9X level, confirming the loss-of-function effect of the identified mutations. Given that some features of affected females are also reported in known ciliopathy syndromes, we examined the role of USP9X in the primary cilium and found that endogenous USP9X localizes along the length of the ciliary axoneme, indicating that its loss of function could indeed disrupt cilium-regulated processes. Absence of dysregulated ciliary parameters in affected female-derived fibroblasts, however, points toward spatiotemporal specificity of ciliary USP9X (dys-)function.
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http://dx.doi.org/10.1016/j.ajhg.2015.12.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4746365PMC
February 2016

De novo loss-of-function mutations in WAC cause a recognizable intellectual disability syndrome and learning deficits in Drosophila.

Eur J Hum Genet 2016 08 13;24(8):1145-53. Epub 2016 Jan 13.

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

Recently WAC was reported as a candidate gene for intellectual disability (ID) based on the identification of a de novo mutation in an individual with severe ID. WAC regulates transcription-coupled histone H2B ubiquitination and has previously been implicated in the 10p12p11 contiguous gene deletion syndrome. In this study, we report on 10 individuals with de novo WAC mutations which we identified through routine (diagnostic) exome sequencing and targeted resequencing of WAC in 2326 individuals with unexplained ID. All but one mutation was expected to lead to a loss-of-function of WAC. Clinical evaluation of all individuals revealed phenotypic overlap for mild ID, hypotonia, behavioral problems and distinctive facial dysmorphisms, including a square-shaped face, deep set eyes, long palpebral fissures, and a broad mouth and chin. These clinical features were also previously reported in individuals with 10p12p11 microdeletion syndrome. To investigate the role of WAC in ID, we studied the importance of the Drosophila WAC orthologue (CG8949) in habituation, a non-associative learning paradigm. Neuronal knockdown of Drosophila CG8949 resulted in impaired learning, suggesting that WAC is required in neurons for normal cognitive performance. In conclusion, we defined a clinically recognizable ID syndrome, caused by de novo loss-of-function mutations in WAC. Independent functional evidence in Drosophila further supported the role of WAC in ID. On the basis of our data WAC can be added to the list of ID genes with a role in transcription regulation through histone modification.
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http://dx.doi.org/10.1038/ejhg.2015.282DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4970694PMC
August 2016

TRIO loss of function is associated with mild intellectual disability and affects dendritic branching and synapse function.

Hum Mol Genet 2016 Mar 31;25(5):892-902. Epub 2015 Dec 31.

Department of Human Genetics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands,

Recently, we marked TRIO for the first time as a candidate gene for intellectual disability (ID). Across diverse vertebrate species, TRIO is a well-conserved Rho GTPase regulator that is highly expressed in the developing brain. However, little is known about the specific events regulated by TRIO during brain development and its clinical impact in humans when mutated. Routine clinical diagnostic testing identified an intragenic de novo deletion of TRIO in a boy with ID. Targeted sequencing of this gene in over 2300 individuals with ID, identified three additional truncating mutations. All index cases had mild to borderline ID combined with behavioral problems consisting of autistic, hyperactive and/or aggressive behavior. Studies in dissociated rat hippocampal neurons demonstrated the enhancement of dendritic formation by suppressing endogenous TRIO, and similarly decreasing endogenous TRIO in organotypic hippocampal brain slices significantly increased synaptic strength by increasing functional synapses. Together, our findings provide new mechanistic insight into how genetic deficits in TRIO can lead to early neuronal network formation by directly affecting both neurite outgrowth and synapse development.
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http://dx.doi.org/10.1093/hmg/ddv618DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4754042PMC
March 2016

Mutations in DDX3X Are a Common Cause of Unexplained Intellectual Disability with Gender-Specific Effects on Wnt Signaling.

Am J Hum Genet 2015 Aug 30;97(2):343-52. Epub 2015 Jul 30.

Department of Medical Genetics and Alberta Children's Hospital Research Institute for Child and Maternal Health, Cumming School of Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada.

Intellectual disability (ID) affects approximately 1%-3% of humans with a gender bias toward males. Previous studies have identified mutations in more than 100 genes on the X chromosome in males with ID, but there is less evidence for de novo mutations on the X chromosome causing ID in females. In this study we present 35 unique deleterious de novo mutations in DDX3X identified by whole exome sequencing in 38 females with ID and various other features including hypotonia, movement disorders, behavior problems, corpus callosum hypoplasia, and epilepsy. Based on our findings, mutations in DDX3X are one of the more common causes of ID, accounting for 1%-3% of unexplained ID in females. Although no de novo DDX3X mutations were identified in males, we present three families with segregating missense mutations in DDX3X, suggestive of an X-linked recessive inheritance pattern. In these families, all males with the DDX3X variant had ID, whereas carrier females were unaffected. To explore the pathogenic mechanisms accounting for the differences in disease transmission and phenotype between affected females and affected males with DDX3X missense variants, we used canonical Wnt defects in zebrafish as a surrogate measure of DDX3X function in vivo. We demonstrate a consistent loss-of-function effect of all tested de novo mutations on the Wnt pathway, and we further show a differential effect by gender. The differential activity possibly reflects a dose-dependent effect of DDX3X expression in the context of functional mosaic females versus one-copy males, which reflects the complex biological nature of DDX3X mutations.
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http://dx.doi.org/10.1016/j.ajhg.2015.07.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4573244PMC
August 2015

B56δ-related protein phosphatase 2A dysfunction identified in patients with intellectual disability.

J Clin Invest 2015 Aug 13;125(8):3051-62. Epub 2015 Jul 13.

Here we report inherited dysregulation of protein phosphatase activity as a cause of intellectual disability (ID). De novo missense mutations in 2 subunits of serine/threonine (Ser/Thr) protein phosphatase 2A (PP2A) were identified in 16 individuals with mild to severe ID, long-lasting hypotonia, epileptic susceptibility, frontal bossing, mild hypertelorism, and downslanting palpebral fissures. PP2A comprises catalytic (C), scaffolding (A), and regulatory (B) subunits that determine subcellular anchoring, substrate specificity, and physiological function. Ten patients had mutations within a highly conserved acidic loop of the PPP2R5D-encoded B56δ regulatory subunit, with the same E198K mutation present in 6 individuals. Five patients had mutations in the PPP2R1A-encoded scaffolding Aα subunit, with the same R182W mutation in 3 individuals. Some Aα cases presented with large ventricles, causing macrocephaly and hydrocephalus suspicion, and all cases exhibited partial or complete corpus callosum agenesis. Functional evaluation revealed that mutant A and B subunits were stable and uncoupled from phosphatase activity. Mutant B56δ was A and C binding-deficient, while mutant Aα subunits bound B56δ well but were unable to bind C or bound a catalytically impaired C, suggesting a dominant-negative effect where mutant subunits hinder dephosphorylation of B56δ-anchored substrates. Moreover, mutant subunit overexpression resulted in hyperphosphorylation of GSK3β, a B56δ-regulated substrate. This effect was in line with clinical observations, supporting a correlation between the ID degree and biochemical disturbance.
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http://dx.doi.org/10.1172/JCI79860DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4623570PMC
August 2015

Refining analyses of copy number variation identifies specific genes associated with developmental delay.

Nat Genet 2014 10 14;46(10):1063-71. Epub 2014 Sep 14.

1] IRCCS (Istituto di Ricovero e Cura a Carattere Scientifico) Associazione Oasi Maria Santissima, Troina, Italy. [2].

Copy number variants (CNVs) are associated with many neurocognitive disorders; however, these events are typically large, and the underlying causative genes are unclear. We created an expanded CNV morbidity map from 29,085 children with developmental delay in comparison to 19,584 healthy controls, identifying 70 significant CNVs. We resequenced 26 candidate genes in 4,716 additional cases with developmental delay or autism and 2,193 controls. An integrated analysis of CNV and single-nucleotide variant (SNV) data pinpointed 10 genes enriched for putative loss of function. Follow-up of a subset of affected individuals identified new clinical subtypes of pediatric disease and the genes responsible for disease-associated CNVs. These genetic changes include haploinsufficiency of SETBP1 associated with intellectual disability and loss of expressive language and truncations of ZMYND11 in individuals with autism, aggression and complex neuropsychiatric features. This combined CNV and SNV approach facilitates the rapid discovery of new syndromes and genes involved in neuropsychiatric disease despite extensive genetic heterogeneity.
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http://dx.doi.org/10.1038/ng.3092DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4177294PMC
October 2014

Chromosomal aberrations in cerebral visual impairment.

Eur J Paediatr Neurol 2014 Nov 22;18(6):677-84. Epub 2014 May 22.

Department of Human Genetics, Radboud university medical center, Nijmegen, The Netherlands; Donders Institute for Brain, Cognition and Behavior, Radboud university medical center, Nijmegen, The Netherlands; Radboud Institute for Health Sciences, Radboud university medical center, Nijmegen, The Netherlands. Electronic address:

Background: Cerebral visual impairment (CVI) is a disorder in projection and/or interpretation of the visual input in the brain and accounts for 27% of the visually impaired children.

Aim: A large cohort of patients with CVI was investigated in order to ascertain the relevance of chromosomal aberrations in the etiology of this disorder.

Methods: 607 patients with CVI and a visual acuity ≤0.3 were assessed for the presence of a chromosomal aberration retrospectively. The observed aberrations were classified for pathogenicity.

Results: A total of 98 chromosomal aberrations were found in 79 persons (13%) of the cohort. In nine persons it was not possible to classify the clinical implication of the aberration, due to lack of detailed information. In 70 persons it was possible to classify the aberration for causality: in 41 patients the aberration was associated with CVI, in 16 it was unknown and in 13 the aberration was unlikely to be associated with CVI. For four aberrations, present in 26 patients, the association with CVI has been reported before: trisomy 21, 1p36 deletion syndrome, 17p13.3 deletion syndrome (Miller-Dieker syndrome) and 22q13.3 deletion syndrome (Phelan-McDermid syndrome). The chromosomal aberrations in another 15 patients were for the first time associated with CVI.

Conclusions: Chromosomal aberrations associated with CVI were found in 7% (41/607) of patients, of which 37% (15/41) have not been reported before in association with CVI. Therefore, in patients with CVI chromosomal investigations should be routinely performed to warrant a good clinical diagnosis and counseling.
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http://dx.doi.org/10.1016/j.ejpn.2014.05.002DOI Listing
November 2014
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