Apostolos Papandreou

Improving diagnosis and broadening the phenotypes in early-onset seizure and severe developmental delay disorders through gene panel analysis

Background We sought to investigate the diagnostic yield and mutation spectrum in previously reported genes for early-onset epilepsy and disorders of severe developmental delay. Methods In 400 patients with these disorders with no known underlying aetiology and no major structural brain anomaly, we analysed 46 genes using a combination of targeted sequencing on an Illumina MiSeq platform and targeted, exon-level microarray copy number analysis. Results We identified causative mutations in 71/400 patients (18%). The diagnostic rate was highest among those with seizure onset within the first two months of life (39%), although overall it was similar in those with and without seizures. The most frequently mutated gene was SCN2A (11 patients, 3%). Other recurrently mutated genes included CDKL5, KCNQ2, SCN8A (six patients each), FOXG1, MECP2, SCN1A, STXBP1 (five patients each), KCNT1, PCDH19, TCF4 (three patients each) and ATP1A3, PRRT2 and SLC9A6 (two patients each). Mutations in EHMT1, GABRB3, LGI1, MBD5, PIGA, UBE3A and ZEB2 were each found in single patients. We found mutations in a number of genes in patients where either the electroclinical features or dysmorphic phenotypes were atypical for the identified gene. In only 11 cases (15%) had the clinician sufficient certainty to specify the mutated gene as the likely cause before testing. Conclusions Our data demonstrate the considerable utility of a gene panel approach in the diagnosis of patients with early-onset epilepsy and severe developmental delay disorders., They provide further insights into the phenotypic spectrum and genotype–phenotype correlations for a number of the causative genes and emphasise the value of exon-level copy number testing in their analysis.

Monoamine neurotransmitter disorders--clinical advances and future perspectives.

The monoamine neurotransmitter disorders are important genetic syndromes that cause disturbances in catecholamine (dopamine, noradrenaline and adrenaline) and serotonin homeostasis. These disorders result in aberrant monoamine synthesis, metabolism and transport. The clinical phenotypes are predominantly neurological, and symptoms resemble other childhood neurological disorders, such as dystonic or dyskinetic cerebral palsy, hypoxic ischaemic encephalopathy and movement disorders. As a consequence, monoamine neurotransmitter disorders are under-recognized and often misdiagnosed. The diagnosis of monoamine neurotransmitter disorders requires detailed clinical assessment, cerebrospinal fluid neurotransmitter analysis and further supportive diagnostic investigations. Prompt and accurate diagnosis of neurotransmitter disorders is paramount, as many are responsive to treatment. The treatment is usually mechanism-based, with the aim to reverse disturbances of monoamine synthesis and/or metabolism. Therapeutic intervention can lead to complete resolution of motor symptoms in some conditions, and considerably improve quality of life in others. In this Review, we discuss the clinical features, diagnosis and management of monoamine neurotransmitter disorders, and consider novel concepts, the latest advances in research and future prospects for therapy.

Mutations in the histone methyltransferase gene KMT2B cause complex early-onset dystonia

Histone lysine methylation, mediated by mixed-lineage leukemia (MLL) proteins, is now known to be critical in the regulation of gene expression, genomic stability, cell cycle and nuclear architecture. Despite MLL proteins being postulated as essential for normal development, little is known about the specific functions of the different MLL lysine methyltransferases. Here we report heterozygous variants in the gene KMT2B (also known as MLL4) in 27 unrelated individuals with a complex progressive childhood-onset dystonia, often associated with a typical facial appearance and characteristic brain magnetic resonance imaging findings. Over time, the majority of affected individuals developed prominent cervical, cranial and laryngeal dystonia. Marked clinical benefit, including the restoration of independent ambulation in some cases, was observed following deep brain stimulation (DBS). These findings highlight a clinically recognizable and potentially treatable form of genetic dystonia, demonstrating the crucial role of KMT2B in the physiological control of voluntary movement.

GABRB3 mutations: a new and emerging cause of early infantile epileptic encephalopathy.

The gamma‐aminobutyric acid type A receptor β3 gene (GABRB3) encodes the β3‐subunit of the gamma‐aminobutyric acid type A (GABAA) receptor, which mediates inhibitory signalling within the central nervous system. Recently, GABRB3 mutations have been identified in a few patients with infantile spasms and Lennox–Gastaut syndrome. We report the clinical and electrographic features of a novel case of GABRB3‐related early‐onset epileptic encephalopathy. Our patient presented with neonatal hypotonia and feeding difficulties, then developed pharmacoresistant epileptic encephalopathy, characterized by multiple seizure types from 3 months of age. Electroencephalography demonstrated ictal generalized and interictal multifocal epileptiform abnormalities. Using a SureSelectXT custom multiple gene panel covering 48 early infantile epileptic encephalopathy/developmental delay genes, a novel de novo GABRB3 heterozygous missense mutation, c.860C>T (p.Thr287Ile), was identified and confirmed on Sanger sequencing. GABRB3 is an emerging cause of early‐onset epilepsy. Novel genetic technologies, such as whole‐exome/genome sequencing and multiple gene panels, will undoubtedly identify further cases, allowing more detailed electroclinical delineation of the GABRB3‐related genotypic and phenotypic spectra.

Delineation of the movement disorders associated with FOXG1 mutations

Objective: The primary objective of this research was to characterize the movement disorders associated with FOXG1 mutations. Methods: We identified patients with FOXG1 mutations who were referred to either a tertiary movement disorder clinic or tertiary epilepsy service and retrospectively reviewed medical records, clinical investigations, neuroimaging, and available video footage. We administered a telephone-based questionnaire regarding the functional impact of the movement disorders and perceived efficacy of treatment to the caregivers of one cohort of participants. Results: We identified 28 patients with FOXG1 mutations, of whom 6 had previously unreported mutations. A wide variety of movement disorders were identified, with dystonia, choreoathetosis, and orolingual/facial dyskinesias most commonly present. Ninety-three percent of patients had a mixed movement disorder phenotype. In contrast to the phenotype classically described with FOXG1 mutations, 4 patients with missense mutations had a milder phenotype, with independent ambulation, spoken language, and normocephaly. Hyperkinetic involuntary movements were a major clinical feature in these patients. Of the symptomatic treatments targeted to control abnormal involuntary movements, most did not emerge as clearly beneficial, although 4 patients had a caregiver-reported response to levodopa. Conclusions: Abnormal involuntary movements are a major feature of FOXG1 mutations. Our study delineates the spectrum of movement disorders and confirms an expanding clinical phenotype. Symptomatic treatment may be considered for severe or disabling cases, although further research regarding potential treatment strategies is necessary.

Familial recurrences of FOXG1-related disorder: Evidence for mosaicism.

FOXG1‐related disorders are caused by heterozygous mutations in FOXG1 and result in a spectrum of neurodevelopmental phenotypes including postnatal microcephaly, intellectual disability with absent speech, epilepsy, chorea, and corpus callosum abnormalities. The recurrence risk for de novo mutations in FOXG1‐related disorders is assumed to be low. Here, we describe three unrelated sets of full siblings with mutations in FOXG1 (c.515_577del63, c.460dupG, and c.572T > G), representing familial recurrence of the disorder. In one family, we have documented maternal somatic mosaicism for the FOXG1 mutation, and all of the families presumably represent parental gonadal (or germline) mosaicism. To our knowledge, mosaicism has not been previously reported in FOXG1‐related disorders. Therefore, this report provides evidence that germline mosaicism for FOXG1 mutations is a likely explanation for familial recurrence and should be considered during recurrence risk counseling for families of children with FOXG1‐related disorders.

Clinical and molecular characterization of KCNT1-related severe early-onset epilepsy

Objective To characterize the phenotypic spectrum, molecular genetic findings, and functional consequences of pathogenic variants in early-onset KCNT1 epilepsy. Methods We identified a cohort of 31 patients with epilepsy of infancy with migrating focal seizures (EIMFS) and screened for variants in KCNT1 using direct Sanger sequencing, a multiple-gene next-generation sequencing panel, and whole-exome sequencing. Additional patients with non-EIMFS early-onset epilepsy in whom we identified KCNT1 variants on local diagnostic multiple gene panel testing were also included. When possible, we performed homology modeling to predict the putative effects of variants on protein structure and function. We undertook electrophysiologic assessment of mutant KCNT1 channels in a xenopus oocyte model system. Results We identified pathogenic variants in KCNT1 in 12 patients, 4 of which are novel. Most variants occurred de novo. Ten patients had a clinical diagnosis of EIMFS, and the other 2 presented with early-onset severe nocturnal frontal lobe seizures. Three patients had a trial of quinidine with good clinical response in 1 patient. Computational modeling analysis implicates abnormal pore function (F346L) and impaired tetramer formation (F502V) as putative disease mechanisms. All evaluated KCNT1 variants resulted in marked gain of function with significantly increased channel amplitude and variable blockade by quinidine. Conclusions Gain-of-function KCNT1 pathogenic variants cause a spectrum of severe focal epilepsies with onset in early infancy. Currently, genotype-phenotype correlations are unclear, although clinical outcome is poor for the majority of cases. Further elucidation of disease mechanisms may facilitate the development of targeted treatments, much needed for this pharmacoresistant genetic epilepsy.

Corrigendum: Mutations in the histone methyltransferase gene KMT2B cause complex early-onset dystonia

Clara D M van Karnebeek, Luisa Bonafé, Xiao-Yan Wen, Maja Tarailo-Graovac, Sara Balzano, Beryl Royer-Bertrand, Angel Ashikov, Livia Garavelli, Isabella Mammi, Licia Turolla, Catherine Breen, Dian Donnai, Valerie Cormier, Delphine Heron, Gen Nishimura, Shinichi Uchikawa, Belinda Campos-Xavier, Antonio Rossi, Thierry Hennet, Koroboshka Brand-Arzamendi, Jacob Rozmus, Keith Harshman, Brian J Stevenson, Enrico Girardi, Giulio Superti-Furga, Tammie Dewan, Alissa Collingridge, Jessie Halparin, Colin J Ross, Margot I Van Allen, Andrea Rossi, Udo F Engelke, Leo A J Kluijtmans, Ed van der Heeft, Herma Renkema, Arjan de Brouwer, Karin Huijben, Fokje Zijlstra, Thorben Heisse, Thomas Boltje, Wyeth W Wasserman, Carlo Rivolta, Sheila Unger, Dirk J Lefeber, Ron A Wevers & Andrea Superti-Furga Nat. Genet. 48, 777–784 (2016); published online 23 May 2016; corrected after print 6 March 2017

Spectrum of movement disorders and neurotransmitter abnormalities in paediatric POLG disease

ObjectivesTo describe the spectrum of movement disorders and cerebrospinal fluid (CSF) neurotransmitter profiles in paediatric patients with POLG disease.MethodsWe identified children with genetically confirmed POLG disease, in whom CSF neurotransmitter analysis had been undertaken. Clinical data were collected retrospectively. CSF neurotransmitter levels were compared to both standardised age-related reference ranges and to non-POLG patients presenting with status epilepticus.ResultsForty-one patients with POLG disease were identified. Almost 50% of the patients had documented evidence of a movement disorder, including non-epileptic myoclonus, choreoathetosis and ataxia. CSF neurotransmitter analysis was undertaken in 15 cases and abnormalities were seen in the majority (87%) of cases tested. In many patients, distinctive patterns were evident, including raised neopterin, homovanillic acid and 5-hydroxyindoleacetic acid levels.ConclusionsChildren with POLG mutations can manifest with a wide spectrum of abnormal movements, which are often prominent features of the clinical syndrome. Underlying pathophysiology is probably multifactorial, and aberrant monoamine metabolism is likely to play a role.

An unusual presentation of paediatric Listeria meningitis with selective spinal grey matter involvement and acute demyelinating polyneuropathy

BACKGROUND Paediatric Listeria meningitis is rare, especially in immuno-competent children, but associated with significant mortality and morbidity and frequent complications. METHODS We report an unusual case of Listeria meningitis in a previously healthy 35 month-old girl with selective spinal grey matter involvement and demyelination in neurophysiological studies. Despite adequate antibiotic treatment, the case was initially complicated by ventriculitis, hydrocephalus and tonsillar herniation through the foramen magnum, requiring external ventricular drainage and subsequent ventriculoperitoneal shunt insertion. Paucity of movements, hypotonia, areflexia and bladder dysfunction then became evident. RESULTS Electromyogram and nerve conduction studies showed acute inflammatory demyelinating polyneuropathy and the patient received intravenous immunoglobulin followed by corticosteroids. MRI scans with contrast revealed extensive whole cord selective grey matter signal changes. She required extensive neurorehabilitation, making gradual (but incomplete) recovery. CONCLUSION Spinal cord involvement is rare in neuro-listeriosis and there no previous paediatric reports of Listeria-related myelitis or demyelinating polyneuropathy. The mechanism behind these presentations is unclear but an auto-immune response to the infection might be considered.