Highlighting the Dystonic Phenotype Related to GNAO1.

BACKGROUND: Most reported patients carrying GNAO1 mutations showed a severe phenotype characterized by early-onset epileptic encephalopathy and/or chorea. OBJECTIVE: The aim was to characterize the clinical and genetic features of patients with mild GNAO1-related phenotype with prominent movement disorders. METHODS: We included patients diagnosed with GNAO1-related movement disorders of delayed onset (>2 years). Patients experiencing either severe or profound intellectual disability or early-onset epileptic encephalopathy were excluded. RESULTS: Twenty-four patients and 1 asymptomatic subject were included. All patients showed dystonia as prominent movement disorder. Dystonia was focal in 1, segmental in 6, multifocal in 4, and generalized in 13. Six patients showed adolescence or adulthood-onset dystonia. Seven patients presented with parkinsonism and 3 with myoclonus. Dysarthria was observed in 19 patients. Mild and moderate ID were present in 10 and 2 patients, respectively. CONCLUSION: We highlighted a mild GNAO1-related phenotype, including adolescent-onset dystonia, broadening the clinical spectrum of this condition. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Biallelic RFC1-expansion in a French multicentric sporadic ataxia cohort.

OBJECTIVE: Cerebellar ataxia with neuropathy and vestibular areflexia syndrome (CANVAS) is a recessively inherited multisystem ataxia compromising cerebellar, vestibular, and sensory nerves, which has been associated to a pathogenic AAGGG(n) biallelic expansion repeat in the RFC1 gene. Our objective was to assess its prevalence in a French cohort of patients with idiopathic sporadic late-onset ataxia (ILOA), idiopathic early-onset ataxia (IEOA), or Multiple System Atrophy of Cerebellar type (MSA-C). METHODS: 163 patients were recruited in 3 French tertiary centers: 100 ILOA, 21 IEOA, and 42 patients with possible or probable MSA-C. RESULTS: A pathogenic biallelic RFC1 AAGGG(n) repeat expansion was found in 15 patients: 15/100 in the ILOA group, but none in the IEOA and MSA-C subgroups. 14/15 patients had a CANVAS phenotype. Only 1/15 had isolated cerebellar ataxia, but also shorter biallelic expansions. Two RFC1 AAGGG(n) alleles were found in 78% of patients with a CANVAS phenotype. In one post-mortem case, the pathophysiological involvement of cerebellum and medullar posterior columns was found. CONCLUSION: Our study confirms the genetic heterogeneity of the CANVAS and that RFC1 repeat expansions should be searched for preferentially in case of unexplained ILOA associated with a sensory neuronopathy, but not particularly in patients classified as MSA-C.

Early-Onset Parkinsonism Is a Manifestation of the PPP2R5D p.E200K Mutation.

PPP2R5D-related neurodevelopmental disorder is characterized by a range of neurodevelopmental and behavioral manifestations. We report the association of early-onset parkinsonism with the PPP2R5D p.E200K mutation. Clinical characterization and exome sequencing were performed on three patients, with postmortem neuropathologic examination for one patient. All patients had mild developmental delay and developed levodopa-responsive parkinsonism between the ages of 25 and 40 years. The PPP2R5D c.598G>A (p.E200K) mutation was identified in all patients. Neuropathologic examination demonstrated uneven, focally severe neuronal loss and gliosis in the substantia nigra pars compacta, without Lewy bodies. Our findings suggest the PPP2R5D p.E200K mutation to be a possible new cause of early-onset parkinsonism. ANN NEUROL 2020;88:1028-1033.

Exome sequencing in 57 patients with self-limited focal epilepsies of childhood with typical or atypical presentations suggests novel candidate genes.

OBJECTIVE: Self-limited focal epilepsies of childhood (SFEC) are amongst the best defined and most frequent epilepsy syndromes affecting children with usually normal developmental milestones. They include core syndromes such as Rolandic epilepsy or "Benign" epilepsy with Centro-Temporal Spikes and the benign occipital epilepsies, the early onset Panayiotopoulos syndrome and the late-onset Gastaut type. Atypical forms exist for all of them. Atypical Rolandic epilepsies are conceptualized as belonging to a continuum reaching from the "benign" RE to the severe end of the Landau-Kleffner (LKS) and Continuous Spike-Waves during Sleep syndromes (CSWS). GRIN2A has been shown to cause the epilepsy-aphasia continuum that includes some patients with atypical Rolandic epilepsy with frequent speech disorders, LKS and CSWS. In the present study, we searched novel genes causing SFEC with typical or atypical presentations. METHODS: Exome sequencing was performed in 57 trios. Patients presented with typical or atypical SFEC, negative for GRIN2A pathogenic variant. RESULTS: We found rare candidate variants in 20 patients. Thirteen had occurred de novo and were mostly associated to atypical Rolandic Epilepsy. Two of them could be considered as disease related: a null variant in GRIN2B and a missense variant in CAMK2A. Others were considered good candidates, including a substitution affecting a splice site in CACNG2 and missense variants in genes encoding enzymes involved in chromatin remodeling. SIGNIFICANCE: Our results further illustrate the fact that atypical SFEC are more likely to have Mendelian inheritance than typical SFEC.

Rare variants in the GABAA receptor subunit ε identified in patients with a wide spectrum of epileptic phenotypes.

BACKGROUND: Epilepsy belongs to a group of chronic and highly heterogeneous brain disorders. Many types of epilepsy and epileptic syndromes are caused by genetic factors. The neural amino acid y-aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the mammalian central nervous system. It regulates activity of channel pores by binding to transmembrane GABA-receptors (GABRs). The GABRs are heteropentamers assembled from different receptor subunits (α1-6, ß1-3, γ1-3, δ, ε, θ, π, and ρ1-3). Several epileptic disorders are caused by mutations in genes encoding single GABRs. METHODS: We applied trio- and single-whole exome sequencing to search for genetic sequence variants associated with a wide range of epileptic phenotypes accompanied by intellectual disability and/or global developmental delay in the investigated patients. RESULTS: We identified four hemizygous sequence variants in the GABAA receptor subunit ε gene (GABRE), including one nonsense (NM_004961.3: c.399C>A, p.Tyr133*), two missense variants (NM_004961.3: c.664G>A, p.Glu222Lys; NM_004961.3: c.1045G>A, p.Val349Ile), and one variant affecting the translation initiation codon (NM_004961.3: c.1A>G, p.Met1?) in four unrelated families. CONCLUSION: Our clinical and molecular genetic findings suggest that GABRE is a likely candidate gene for epilepsy. Nevertheless, functional studies are necessary to better understand pathogenicity of the GABRE-mutations and their associations with epileptic phenotypes.

Biallelic PDE2A variants: a new cause of syndromic paroxysmal dyskinesia.

Cause of complex dyskinesia remains elusive in some patients. A homozygous missense variant leading to drastic decrease of PDE2A enzymatic activity was reported in one patient with childhood-onset choreodystonia preceded by paroxysmal dyskinesia and associated with cognitive impairment and interictal EEG abnormalities. Here, we report three new cases with biallelic PDE2A variants identified by trio whole-exome sequencing. Mitochondria network was analyzed after Mitotracker™ Red staining in control and mutated primary fibroblasts. Analysis of retrospective video of patients' movement disorder and refinement of phenotype was carried out. We identified a homozygous gain of stop codon variant c.1180C>T; p.(Gln394*) in PDE2A in siblings and compound heterozygous variants in young adult: a missense c.446C>T; p.(Pro149Leu) and splice-site variant c.1922+5G>A predicted and shown to produce an out of frame transcript lacking exon 22. All three patients had cognitive impairment or developmental delay. The phenotype of the two oldest patients, aged 9 and 26, was characterized by childhood-onset refractory paroxysmal dyskinesia initially misdiagnosed as epilepsy due to interictal EEG abnormalities. The youngest patient showed a proven epilepsy at the age of 4 months and no paroxysmal dyskinesia at 15 months. Interestingly, analysis of the fibroblasts with the biallelic variants in PDE2A variants revealed mitochondria network morphology changes. Together with previously reported case, our three patients confirm that biallelic PDE2A variants are a cause of childhood-onset refractory paroxysmal dyskinesia with cognitive impairment, sometimes associated with choreodystonia and interictal baseline EEG abnormalities or epilepsy.

Increased diagnostic yield in complex dystonia through exome sequencing.

INTRODUCTION: A strategy based on targeted gene panel sequencing identifies possibly pathogenic variants in fewer than 20% of cases in early-onset and familial form of dystonia. By using Whole Exome Sequencing (WES), we aimed to identify the missing genetic causes in dystonic patients without diagnosis despite gene panel sequencing. MATERIAL AND METHODS: WES was applied to DNA samples from 32 patients with early-onset or familial dystonia investigated by sequencing of a 127 movement disorders-associated gene panel. Dystonia was described according to the familial history, body distribution, evolution pattern, age of onset, associated symptoms and associated movement disorders. Rate of diagnoses was evaluated for each clinical feature. RESULTS: We identified causative variants for 11 patients from 9 families in CTNNB1, SUCLG1, NUS1, CNTNAP1, KCNB1, RELN, GNAO1, HIBCH, ADCK3 genes, yielding an overall diagnostic rate of 34.4%. Diagnostic yield was higher in complex dystonia compared to non-complex dystonia (66.7%-5.9%; p < 0.002), especially in patients showing intellectual disability compared to the patients without intellectual disability (87.5%-16.7%; p < 0.002). CONCLUSION: Our approach suggests WES as an efficient tool to improve the diagnostic yield after gene panel sequencing in dystonia. Larger study are warranted to confirm a potential genetic overlap between neurodevelopmental diseases and dystonia.

Expanding the clinical and EEG spectrum of CNKSR2-related encephalopathy with status epilepticus during slow sleep (ESES).

OBJECTIVE: To investigate the clinical and EEG features of Encephalopathy with Status Epilepticus during slow Sleep (ESES) related to CNKSR2 pathogenic variants. METHODS: Detailed clinical history, repeated wakefulness/overnight sleep EEGs, brain MRI were collected in five patients, including one female, with CNKSR2-related ESES. RESULTS: Neurodevelopment in infancy was normal in two patients, delayed in three. Epilepsy onset (age range: 2-6 years) was associated with appearance or aggravation of cognitive impairment, language regression and/or behavioral disorders. Worsening of epilepsy and of cognitive/behavioral disturbances paralleled by enhancement of non-rapid eye movement (NREM) sleep-related, frontally predominant, EEG epileptic discharges [spike-wave-index (SWI): range 60-96%] was consistent with ESES. In three patients, episodes of absence status epilepticus or aggravation of atypical absences occurred, in this latter case associated with striking increment of awake SWI. Speech/oro-motor dyspraxia was diagnosed in four patients. In two patients, long-term follow-up showed epilepsy remission and persistence of mild/moderate cognitive disorders and behavioral disturbances into adulthood. CONCLUSIONS: Novel findings of our study are occurrence also in females, normal neurodevelopment before epilepsy onset, epilepsy aggravation associated with enhanced awake SWI, mild/moderate evolution in adulthood and language disorder due to speech/oro-motor dyspraxia. SIGNIFICANCE: Our findings expand the phenotypic spectrum of CNKSR2-related ESES.

Conditional switching of KIF2A mutation provides new insights into cortical malformation pathogeny.

By using the Cre-mediated genetic switch technology, we were able to successfully generate a conditional knock-in mouse, bearing the KIF2A p.His321Asp missense point variant, identified in a subject with malformations of cortical development. These mice present with neuroanatomical anomalies and microcephaly associated with behavioral deficiencies and susceptibility to epilepsy, correlating with the described human phenotype. Using the flexibility of this model, we investigated RosaCre-, NestinCre- and NexCre-driven expression of the mutation to dissect the pathophysiological mechanisms underlying neurodevelopmental cortical abnormalities. We show that the expression of the p.His321Asp pathogenic variant increases apoptosis and causes abnormal multipolar to bipolar transition in newborn neurons, providing therefore insights to better understand cortical organization and brain growth defects that characterize KIF2A-related human disorders. We further demonstrate that the observed cellular phenotypes are likely to be linked to deficiency in the microtubule depolymerizing function of KIF2A.

Loss-of-Function Mutations in NR4A2 Cause Dopa-Responsive Dystonia Parkinsonism.

BACKGROUND: The group of dystonia genes is expanding, and mutations of these genes have been associated with various combined dystonia syndromes. Among the latter, the cause of some dystonia parkinsonism cases remains unknown. OBJECTIVE: To report patients with early-onset dystonia parkinsonism as a result of loss-of-function mutations in nuclear receptor subfamily 4 group A member 2. METHODS: Phenotypic characterization and exome sequencing were carried out in 2 families. RESULTS: The 2 patients reported here both had a history of mild intellectual disability in childhood and subsequently developed dystonia parkinsonism in early adulthood. Brain magnetic resonance imaging was normal, and DATscan suggested bilateral dopaminergic denervation. Two frameshift mutations in NR4A2 were identified: a de novo insertion (NM_006186.3; c.326dupA) in the first case and another small insertion (NM_006186.3; c.881dupA) in the second. CONCLUSIONS: NR4A2 haploinsufficiency mutations have been recently reported in neurodevelopmental phenotypes. Our findings indicate that dystonia and/or parkinsonism may appear years after initial symptoms. Mutations in NR4A2 should be considered in patients with unexplained dystonia parkinsonism. © 2020 International Parkinson and Movement Disorder Society.

Intronic ATTTC repeat expansions in STARD7 in familial adult myoclonic epilepsy linked to chromosome 2.

Familial Adult Myoclonic Epilepsy (FAME) is characterised by cortical myoclonic tremor usually from the second decade of life and overt myoclonic or generalised tonic-clonic seizures. Four independent loci have been implicated in FAME on chromosomes (chr) 2, 3, 5 and 8. Using whole genome sequencing and repeat primed PCR, we provide evidence that chr2-linked FAME (FAME2) is caused by an expansion of an ATTTC pentamer within the first intron of STARD7. The ATTTC expansions segregate in 158/158 individuals typically affected by FAME from 22 pedigrees including 16 previously reported families recruited worldwide. RNA sequencing from patient derived fibroblasts shows no accumulation of the AUUUU or AUUUC repeat sequences and STARD7 gene expression is not affected. These data, in combination with other genes bearing similar mutations that have been implicated in FAME, suggest ATTTC expansions may cause this disorder, irrespective of the genomic locus involved.

Unstable TTTTA/TTTCA expansions in MARCH6 are associated with Familial Adult Myoclonic Epilepsy type 3.

Familial Adult Myoclonic Epilepsy (FAME) is a genetically heterogeneous disorder characterized by cortical tremor and seizures. Intronic TTTTA/TTTCA repeat expansions in SAMD12 (FAME1) are the main cause of FAME in Asia. Using genome sequencing and repeat-primed PCR, we identify another site of this repeat expansion, in MARCH6 (FAME3) in four European families. Analysis of single DNA molecules with nanopore sequencing and molecular combing show that expansions range from 3.3 to 14 kb on average. However, we observe considerable variability in expansion length and structure, supporting the existence of multiple expansion configurations in blood cells and fibroblasts of the same individual. Moreover, the largest expansions are associated with micro-rearrangements occurring near the expansion in 20% of cells. This study provides further evidence that FAME is caused by intronic TTTTA/TTTCA expansions in distinct genes and reveals that expansions exhibit an unexpectedly high somatic instability that can ultimately result in genomic rearrangements.

Update on the genetics of the epilepsy-aphasia spectrum and role of GRIN2A mutations.

Formerly idiopathic, focal epilepsies (IFE) are self-limiting, "age-related" diseases that mainly occur during critical developmental periods. Childhood epilepsy with centrotemporal spikes, or Rolandic epilepsy (RE), is the most frequent form of IFE. Together with the Landau-Kleffner syndrome and the epileptic Encephalopathy related to Status Epilepticus during slow Sleep syndrome (ESES), RE is part of a single and continuous spectrum of childhood epilepsies and epileptic encephalopathies with acquired cognitive, behavioral and speech and/or language impairment, known as the epilepsy-aphasia spectrum (EAS). The pathophysiology has long been attributed to an elusive and complex interplay between brain development and maturation processes on the one hand, and susceptibility genes on the other hand. Studies based on the variable combination of molecular cytogenetics, Sanger and next-generation sequencing tools, and functional assays have led to the identification and validation of genetic mutations in the GRIN2A gene that can directly cause various types of EAS disorders. The recent identification of GRIN2A defects in EAS represents a first and major break-through in our understanding of the underlying pathophysiological mechanisms. In this review, we describe the current knowledge on the genetic architecture of IFE.

TUBG1 missense variants underlying cortical malformations disrupt neuronal locomotion and microtubule dynamics but not neurogenesis.

De novo heterozygous missense variants in the γ-tubulin gene TUBG1 have been linked to human malformations of cortical development associated with intellectual disability and epilepsy. Here, we investigated through in-utero electroporation and in-vivo studies, how four of these variants affect cortical development. We show that TUBG1 mutants affect neuronal positioning, disrupting the locomotion of new-born neurons but without affecting progenitors' proliferation. We further demonstrate that pathogenic TUBG1 variants are linked to reduced microtubule dynamics but without major structural nor functional centrosome defects in subject-derived fibroblasts. Additionally, we developed a knock-in Tubg1Y92C/+ mouse model and assessed consequences of the mutation. Although centrosomal positioning in bipolar neurons is correct, they fail to initiate locomotion. Furthermore, Tubg1Y92C/+ animals show neuroanatomical and behavioral defects and increased epileptic cortical activity. We show that Tubg1Y92C/+ mice partially mimic the human phenotype and therefore represent a relevant model for further investigations of the physiopathology of cortical malformations.

Correction to: The landscape of epilepsy-related GATOR1 variants.

The original version of this Article contained an error in the author list where the corresponding author Stéphanie Baulac was repeated twice. This has now been corrected in the HTML, the PDF was correct at the time of publication.

The landscape of epilepsy-related GATOR1 variants.

PURPOSE: To define the phenotypic and mutational spectrum of epilepsies related to DEPDC5, NPRL2 and NPRL3 genes encoding the GATOR1 complex, a negative regulator of the mTORC1 pathway METHODS: We analyzed clinical and genetic data of 73 novel probands (familial and sporadic) with epilepsy-related variants in GATOR1-encoding genes and proposed new guidelines for clinical interpretation of GATOR1 variants. RESULTS: The GATOR1 seizure phenotype consisted mostly in focal seizures (e.g., hypermotor or frontal lobe seizures in 50%), with a mean age at onset of 4.4 years, often sleep-related and drug-resistant (54%), and associated with focal cortical dysplasia (20%). Infantile spasms were reported in 10% of the probands. Sudden unexpected death in epilepsy (SUDEP) occurred in 10% of the families. Novel classification framework of all 140 epilepsy-related GATOR1 variants (including the variants of this study) revealed that 68% are loss-of-function pathogenic, 14% are likely pathogenic, 15% are variants of uncertain significance and 3% are likely benign. CONCLUSION: Our data emphasize the increasingly important role of GATOR1 genes in the pathogenesis of focal epilepsies (>180 probands to date). The GATOR1 phenotypic spectrum ranges from sporadic early-onset epilepsies with cognitive impairment comorbidities to familial focal epilepsies, and SUDEP.

Correction: The landscape of epilepsy-related GATOR1 variants.

The original version of this article contained an error in the spelling of the author Erik H. Niks, which was incorrectly given as Erik Niks. This has now been corrected in both the PDF and HTML versions of the article.

GRIN2A-related disorders: genotype and functional consequence predict phenotype.

Alterations of the N-methyl-d-aspartate receptor (NMDAR) subunit GluN2A, encoded by GRIN2A, have been associated with a spectrum of neurodevelopmental disorders with prominent speech-related features, and epilepsy. We performed a comprehensive assessment of phenotypes with a standardized questionnaire in 92 previously unreported individuals with GRIN2A-related disorders. Applying the criteria of the American College of Medical Genetics and Genomics to all published variants yielded 156 additional cases with pathogenic or likely pathogenic variants in GRIN2A, resulting in a total of 248 individuals. The phenotypic spectrum ranged from normal or near-normal development with mild epilepsy and speech delay/apraxia to severe developmental and epileptic encephalopathy, often within the epilepsy-aphasia spectrum. We found that pathogenic missense variants in transmembrane and linker domains (misTMD+Linker) were associated with severe developmental phenotypes, whereas missense variants within amino terminal or ligand-binding domains (misATD+LBD) and null variants led to less severe developmental phenotypes, which we confirmed in a discovery (P = 10-6) as well as validation cohort (P = 0.0003). Other phenotypes such as MRI abnormalities and epilepsy types were also significantly different between the two groups. Notably, this was paralleled by electrophysiology data, where misTMD+Linker predominantly led to NMDAR gain-of-function, while misATD+LBD exclusively caused NMDAR loss-of-function. With respect to null variants, we show that Grin2a+/- cortical rat neurons also had reduced NMDAR function and there was no evidence of previously postulated compensatory overexpression of GluN2B. We demonstrate that null variants and misATD+LBD of GRIN2A do not only share the same clinical spectrum (i.e. milder phenotypes), but also result in similar electrophysiological consequences (loss-of-function) opposing those of misTMD+Linker (severe phenotypes; predominantly gain-of-function). This new pathomechanistic model may ultimately help in predicting phenotype severity as well as eligibility for potential precision medicine approaches in GRIN2A-related disorders.