Publications by authors named "Georgie Hollingsworth"

5 Publications

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Transcriptome analysis of a ring chromosome 20 patient cohort.

Epilepsia 2021 Jan 18;62(1):e22-e28. Epub 2020 Nov 18.

Department of Medicine, Epilepsy Research Centre, University of Melbourne, Austin Health, Heidelberg, Victoria, Australia.

Ring chromosomes occur when the ends of normally rod-shaped chromosomes fuse. In ring chromosome 20 (ring 20), intellectual disability and epilepsy are usually present, even if there is no deleted coding material; the mechanism by which individuals with complete ring chromosomes develop seizures and other phenotypic abnormalities is not understood. We investigated altered gene transcription as a contributing factor by performing RNA-sequencing (RNA-seq) analysis on blood from seven patients with ring 20, and 11 first-degree relatives (all parents). Geographic analysis did not identify altered expression in peritelomeric or other specific chromosome 20 regions. RNA-seq analysis revealed 97 genes potentially differentially expressed in ring 20 patients. These included one epilepsy gene, NPRL3, but this finding was not confirmed on reverse transcription Droplet Digital polymerase chain reaction analysis. Molecular studies of structural chromosomal anomalies such as ring chromosome are challenging and often difficult to interpret because many patients are mosaic, and there may be genome-wide chromosomal instability affecting gene expression. Our findings nevertheless suggest that peritelomeric altered transcription is not the likely pathogenic mechanism in ring 20. Underlying genetic mechanisms are likely complex and may involve differential expression of many genes, the majority of which may not be located on chromosome 20.
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January 2021

NEXMIF encephalopathy: an X-linked disorder with male and female phenotypic patterns.

Genet Med 2021 Feb 4;23(2):363-373. Epub 2020 Nov 4.

Epilepsy Research Centre, Department of Medicine, Austin Health, University of Melbourne, Melbourne, VIC, Australia.

Purpose: Pathogenic variants in the X-linked gene NEXMIF (previously KIAA2022) are associated with intellectual disability (ID), autism spectrum disorder, and epilepsy. We aimed to delineate the female and male phenotypic spectrum of NEXMIF encephalopathy.

Methods: Through an international collaboration, we analyzed the phenotypes and genotypes of 87 patients with NEXMIF encephalopathy.

Results: Sixty-three females and 24 males (46 new patients) with NEXMIF encephalopathy were studied, with 30 novel variants. Phenotypic features included developmental delay/ID in 86/87 (99%), seizures in 71/86 (83%) and multiple comorbidities. Generalized seizures predominated including myoclonic seizures and absence seizures (both 46/70, 66%), absence with eyelid myoclonia (17/70, 24%), and atonic seizures (30/70, 43%). Males had more severe developmental impairment; females had epilepsy more frequently, and varied from unaffected to severely affected. All NEXMIF pathogenic variants led to a premature stop codon or were deleterious structural variants. Most arose de novo, although X-linked segregation occurred for both sexes. Somatic mosaicism occurred in two males and a family with suspected parental mosaicism.

Conclusion: NEXMIF encephalopathy is an X-linked, generalized developmental and epileptic encephalopathy characterized by myoclonic-atonic epilepsy overlapping with eyelid myoclonia with absence. Some patients have developmental encephalopathy without epilepsy. Males have more severe developmental impairment. NEXMIF encephalopathy arises due to loss-of-function variants.
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February 2021

Aberrant Inclusion of a Poison Exon Causes Dravet Syndrome and Related SCN1A-Associated Genetic Epilepsies.

Am J Hum Genet 2018 12;103(6):1022-1029

Division of Genetic Medicine, Department of Pediatrics, University of Washington, Seattle, WA 98195, USA. Electronic address:

Developmental and epileptic encephalopathies (DEEs) are a group of severe epilepsies characterized by refractory seizures and developmental impairment. Sequencing approaches have identified causal genetic variants in only about 50% of individuals with DEEs. This suggests that unknown genetic etiologies exist, potentially in the ∼98% of human genomes not covered by exome sequencing (ES). Here we describe seven likely pathogenic variants in regions outside of the annotated coding exons of the most frequently implicated epilepsy gene, SCN1A, encoding the alpha-1 sodium channel subunit. We provide evidence that five of these variants promote inclusion of a "poison" exon that leads to reduced amounts of full-length SCN1A protein. This mechanism is likely to be broadly relevant to human disease; transcriptome studies have revealed hundreds of poison exons, including some present within genes encoding other sodium channels and in genes involved in neurodevelopment more broadly. Future research on the mechanisms that govern neuronal-specific splicing behavior might allow researchers to co-opt this system for RNA therapeutics.
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December 2018

High Rate of Recurrent De Novo Mutations in Developmental and Epileptic Encephalopathies.

Fadi F Hamdan Candace T Myers Patrick Cossette Philippe Lemay Dan Spiegelman Alexandre Dionne Laporte Christina Nassif Ousmane Diallo Jean Monlong Maxime Cadieux-Dion Sylvia Dobrzeniecka Caroline Meloche Kyle Retterer Megan T Cho Jill A Rosenfeld Weimin Bi Christine Massicotte Marguerite Miguet Ledia Brunga Brigid M Regan Kelly Mo Cory Tam Amy Schneider Georgie Hollingsworth David R FitzPatrick Alan Donaldson Natalie Canham Edward Blair Bronwyn Kerr Andrew E Fry Rhys H Thomas Joss Shelagh Jane A Hurst Helen Brittain Moira Blyth Robert Roger Lebel Erica H Gerkes Laura Davis-Keppen Quinn Stein Wendy K Chung Sara J Dorison Paul J Benke Emily Fassi Nicole Corsten-Janssen Erik-Jan Kamsteeg Frederic T Mau-Them Ange-Line Bruel Alain Verloes Katrin Õunap Monica H Wojcik Dara V F Albert Sunita Venkateswaran Tyson Ware Dean Jones Yu-Chi Liu Shekeeb S Mohammad Peyman Bizargity Carlos A Bacino Vincenzo Leuzzi Simone Martinelli Bruno Dallapiccola Marco Tartaglia Lubov Blumkin Klaas J Wierenga Gabriela Purcarin James J O'Byrne Sylvia Stockler Anna Lehman Boris Keren Marie-Christine Nougues Cyril Mignot Stéphane Auvin Caroline Nava Susan M Hiatt Martina Bebin Yunru Shao Fernando Scaglia Seema R Lalani Richard E Frye Imad T Jarjour Stéphanie Jacques Renee-Myriam Boucher Emilie Riou Myriam Srour Lionel Carmant Anne Lortie Philippe Major Paola Diadori François Dubeau Guy D'Anjou Guillaume Bourque Samuel F Berkovic Lynette G Sadleir Philippe M Campeau Zoha Kibar Ronald G Lafrenière Simon L Girard Saadet Mercimek-Mahmutoglu Cyrus Boelman Guy A Rouleau Ingrid E Scheffer Heather C Mefford Danielle M Andrade Elsa Rossignol Berge A Minassian Jacques L Michaud

Am J Hum Genet 2017 Nov;101(5):664-685

Centre Hospitalier Universitaire Sainte-Justine Research Center, Montreal, QC H3T1C5, Canada; Department of Neurosciences, Université de Montréal, Montreal, QC H3T1J4, Canada; Department of Pediatrics, Université de Montréal, Montreal, QC H3T1C5, Canada. Electronic address:

Developmental and epileptic encephalopathy (DEE) is a group of conditions characterized by the co-occurrence of epilepsy and intellectual disability (ID), typically with developmental plateauing or regression associated with frequent epileptiform activity. The cause of DEE remains unknown in the majority of cases. We performed whole-genome sequencing (WGS) in 197 individuals with unexplained DEE and pharmaco-resistant seizures and in their unaffected parents. We focused our attention on de novo mutations (DNMs) and identified candidate genes containing such variants. We sought to identify additional subjects with DNMs in these genes by performing targeted sequencing in another series of individuals with DEE and by mining various sequencing datasets. We also performed meta-analyses to document enrichment of DNMs in candidate genes by leveraging our WGS dataset with those of several DEE and ID series. By combining these strategies, we were able to provide a causal link between DEE and the following genes: NTRK2, GABRB2, CLTC, DHDDS, NUS1, RAB11A, GABBR2, and SNAP25. Overall, we established a molecular diagnosis in 63/197 (32%) individuals in our WGS series. The main cause of DEE in these individuals was de novo point mutations (53/63 solved cases), followed by inherited mutations (6/63 solved cases) and de novo CNVs (4/63 solved cases). De novo missense variants explained a larger proportion of individuals in our series than in other series that were primarily ascertained because of ID. Moreover, these DNMs were more frequently recurrent than those identified in ID series. These observations indicate that the genetic landscape of DEE might be different from that of ID without epilepsy.
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November 2017

encephalopathy: A new disease of vesicle fission.

Neurology 2017 Jul 30;89(4):385-394. Epub 2017 Jun 30.

Author affiliations are provided at the end of the article.

Objective: To evaluate the phenotypic spectrum caused by mutations in dynamin 1 (), encoding the presynaptic protein DNM1, and to investigate possible genotype-phenotype correlations and predicted functional consequences based on structural modeling.

Methods: We reviewed phenotypic data of 21 patients (7 previously published) with mutations. We compared mutation data to known functional data and undertook biomolecular modeling to assess the effect of the mutations on protein function.

Results: We identified 19 patients with de novo mutations in and a sibling pair who had an inherited mutation from a mosaic parent. Seven patients (33.3%) carried the recurrent p.Arg237Trp mutation. A common phenotype emerged that included severe to profound intellectual disability and muscular hypotonia in all patients and an epilepsy characterized by infantile spasms in 16 of 21 patients, frequently evolving into Lennox-Gastaut syndrome. Two patients had profound global developmental delay without seizures. In addition, we describe a single patient with normal development before the onset of a catastrophic epilepsy, consistent with febrile infection-related epilepsy syndrome at 4 years. All mutations cluster within the GTPase or middle domains, and structural modeling and existing functional data suggest a dominant-negative effect on DMN1 function.

Conclusions: The phenotypic spectrum of -related encephalopathy is relatively homogeneous, in contrast to many other genetic epilepsies. Up to one-third of patients carry the recurrent p.Arg237Trp variant, which is now one of the most common recurrent variants in epileptic encephalopathies identified to date. Given the predicted dominant-negative mechanism of this mutation, this variant presents a prime target for therapeutic intervention.
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July 2017