Sharon Aharoni

New Hyperekplexia Mutations Provide Insight into Glycine Receptor Assembly, Trafficking, and Activation Mechanisms

Background: Hyperekplexia mutations have provided much information about glycine receptor structure and function. Results: We identified and characterized nine new mutations. Dominant mutations resulted in spontaneous activation, whereas recessive mutations precluded surface expression. Conclusion: These data provide insight into glycine receptor activation mechanisms and surface expression determinants. Significance: The results enhance our understanding of hyperekplexia pathology and glycine receptor structure-function. Hyperekplexia is a syndrome of readily provoked startle responses, alongside episodic and generalized hypertonia, that presents within the first month of life. Inhibitory glycine receptors are pentameric ligand-gated ion channels with a definitive and clinically well stratified linkage to hyperekplexia. Most hyperekplexia cases are caused by mutations in the α1 subunit of the human glycine receptor (hGlyR) gene (GLRA1). Here we analyzed 68 new unrelated hyperekplexia probands for GLRA1 mutations and identified 19 mutations, of which 9 were novel. Electrophysiological analysis demonstrated that the dominant mutations p.Q226E, p.V280M, and p.R414H induced spontaneous channel activity, indicating that this is a recurring mechanism in hGlyR pathophysiology. p.Q226E, at the top of TM1, most likely induced tonic activation via an enhanced electrostatic attraction to p.R271 at the top of TM2, suggesting a structural mechanism for channel activation. Receptors incorporating p.P230S (which is heterozygous with p.R65W) desensitized much faster than wild type receptors and represent a new TM1 site capable of modulating desensitization. The recessive mutations p.R72C, p.R218W, p.L291P, p.D388A, and p.E375X precluded cell surface expression unless co-expressed with α1 wild type subunits. The recessive p.E375X mutation resulted in subunit truncation upstream of the TM4 domain. Surprisingly, on the basis of three independent assays, we were able to infer that p.E375X truncated subunits are incorporated into functional hGlyRs together with unmutated α1 or α1 plus β subunits. These aberrant receptors exhibit significantly reduced glycine sensitivity. To our knowledge, this is the first suggestion that subunits lacking TM4 domains might be incorporated into functional pentameric ligand-gated ion channel receptors.

Broad Phenotypic Heterogeneity due to a Novel SCN1A Mutation in a Family With Genetic Epilepsy With Febrile Seizures Plus

Genetic (generalized) epilepsy with febrile seizures plus is a familial epilepsy syndrome with marked phenotypic heterogeneity ranging from simple febrile seizure to severe phenotypes. Here we report on a large Israeli family with genetic (generalized) epilepsy with febrile seizures plus and 14 affected individuals. A novel SCN1A missense mutation in exon 21 (p.K1372E) was identified in all affected individuals and 3 unaffected carriers. The proband had Dravet syndrome, whereas febrile seizure plus phenotypes were present in all other affected family members. Simple febrile seizures were not observed. Phenotypes were found at both extremes of the genetic (generalized) epilepsy with febrile seizures plus spectrum and distribution of phenotypes suggested modifying familial, possibly genetic factors. We suggest that families with extreme phenotype distributions can represent prime candidates for the identification of genetic or environmental modifiers.

The Ketogenic Diet 2011: How It Works

Although the ketogenic diet (KD) has been widely accepted as a legitimate and successful therapy for epilepsy and other neurological disorders, its mechanism of action remains an enigma. The use of the KD causes major metabolic changes. The most significant of them seems to be the situation of chronic ketosis, but there are others as well, for instance, high level of polyunsaturated fatty acids (PUFAs). These “primary” influences lead to “secondary”, in part adaptive, effects, for instance changes in mitochondrial density and gene expression. Clinically, the influences of the diet are considered as anticonvulsive and neuroprotective, although neuroprotection can also lead to prevention of seizures. Potential clinical implications of these mechanisms are discussed.

Homozygous Mutations in VAMP1 Cause a Presynaptic Congenital Myasthenic Syndrome

We report 2 families with undiagnosed recessive presynaptic congenital myasthenic syndrome (CMS). Whole exome or genome sequencing identified segregating homozygous variants in VAMP1: c.51_64delAGGTGGGGGTCCCC in a Kuwaiti family and c.146G>C in an Israeli family. VAMP1 is crucial for vesicle fusion at presynaptic neuromuscular junction (NMJ). Electrodiagnostic examination showed severely low compound muscle action potentials and presynaptic impairment. We assessed the effect of the nonsense mutation on mRNA levels and evaluated the NMJ transmission in VAMP1lew/lew mice, observing neurophysiological features of presynaptic impairment, similar to the patients. Taken together, our findings highlight VAMP1 homozygous mutations as a cause of presynaptic CMS. Ann Neurol 2017;81:597–603

Congenital myasthenic syndrome in Israel: Genetic and clinical characterization

The objective of the study was to evaluate the epidemiology of patients with congenital myasthenic syndrome (CMS) in Israel. Targeted mutation analysis was performed based on the clinical symptoms and electrophysiological findings for known CMS. Additional specific tests were performed in patients of Iranian and/or Iraqi Jewish origin. All medical records were reviewed and clinical data, genetic mutations and outcomes were recorded. Forty-five patients with genetic mutations in known CMS genes from 35 families were identified. Mutations in RAPSN were identified in 13 kinships in Israel. The most common mutation was c.-38A>G detected in 8 patients of Iranian and/or Iraqi Jewish origin. Four different recessive mutations in COLQ were identified in 11 kinships, 10 of which were of Muslim-Arab descent. Mutations in CHRNE were identified in 7 kinships. Less commonly detected mutations were in CHRND, CHAT, GFPT1 and DOK7. In conclusion, mutations in RAPSN and COLQ are the most common causes of CMS in our cohort. Specific mutations in COLQ, RAPSN, and CHRNE occur in specific ethnic populations and should be taken into account when the diagnosis of a CMS is suspected.

Variable Myopathic Presentation in a Single Family with Novel Skeletal RYR1 Mutation

We describe an autosomal recessive heterogeneous congenital myopathy in a large consanguineous family. The disease is characterized by variable severity, progressive course in 3 of 4 patients, myopathic face without ophthalmoplegia and proximal muscle weakness. Absence of cores was noted in all patients. Genome wide linkage analysis revealed a single locus on chromosome 19q13 with Zmax = 3.86 at θ = 0.0 and homozygosity of the polymorphic markers at this locus in patients. Direct sequencing of the main candidate gene within the candidate region, RYR1, was performed. A novel homozygous A to G nucleotide substitution (p.Y3016C) within exon 60 of the RYR1 gene was found in patients. ARMS PCR was used to screen for the mutation in all available family members and in an additional 150 healthy individuals. This procedure confirmed sequence analysis and did not reveal the A to G mutation (p.Y3016C) in 300 chromosomes from healthy individuals. Functional analysis on EBV immortalized cell lines showed no effect of the mutation on RyR1 pharmacological activation or the content of intracellular Ca2+ stores. Western blot analysis demonstrated a significant reduction of the RyR1 protein in the patient’s muscle concomitant with a reduction of the DHPRα1.1 protein. This novel mutation resulting in RyR1 protein decrease causes heterogeneous clinical presentation, including slow progression course and absence of centrally localized cores on muscle biopsy. We suggest that RYR1 related myopathy should be considered in a wide variety of clinical and pathological presentation in childhood myopathies.

Striking Phenotypic Variability in Familial TRPV4-Axonal Neuropathy Spectrum Disorder

Striking Phenotypic Variability in Familial TRPV4-Axonal Neuropathy Spectrum Disorder Sharon Aharoni, Gaurav Harlalka, Amaka Offiah, Avinoam Shuper, Andrew H. Crosby, and Meriel McEntagart* Department of Neurology, Schneider Children’s Medical Center, Petach Tikva, Israel Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel Centre for Medical Genetics, St. George’s University London, London, UK Academic Unit of Child Health, Sheffield Children’s NHS Foundation Trust, Sheffield, UK

Novel homozygous missense mutation in GAN associated with Charcot-Marie-Tooth disease type 2 in a large consanguineous family from Israel

BackgroundCMT-2 is a clinically and genetically heterogeneous group of peripheral axonal neuropathies characterized by slowly progressive weakness and atrophy of distal limb muscles resulting from length-dependent motor and sensory neurodegeneration. Classical giant axonal neuropathy (GAN) is an autosomal recessively inherited progressive neurodegenerative disorder of the peripheral and central nervous systems, typically diagnosed in early childhood and resulting in death by the end of the third decade. Distinctive phenotypic features are the presence of “kinky” hair and long eyelashes. The genetic basis of the disease has been well established, with over 40 associated mutations identified in the gene GAN, encoding the BTB-KELCH protein gigaxonin, involved in intermediate filament regulation.MethodsAn Illumina Human CytoSNP-12 array followed by whole exome sequence analysis was used to identify the disease associated gene mutation in a large consanguineous family diagnosed with Charcot-Marie-Tooth disease type 2 (CMT-2) from which all but one affected member had straight hair.ResultsHere we report the identification of a novel GAN missense mutation underlying the CMT-2 phenotype observed in this family. Although milder forms of GAN, with and without the presence of kinky hair have been reported previously, a phenotype distinct from that was investigated in this study. All family members lacked common features of GAN, including ataxia, nystagmus, intellectual disability, seizures, and central nervous system involvement.ConclusionsOur findings broaden the spectrum of phenotypes associated with GAN mutations and emphasize a need to proceed with caution when providing families with diagnostic or prognostic information based on either clinical or genetic findings alone.

MELAS syndrome associated with both A3243G-tRNALeu mutation and multiple mitochondrial DNA deletions

The syndrome of mitochondrial encephalopathy, lactic acidosis, and stroke-like episode (MELAS) is characterized clinically by recurrent focal neurological deficits, epilepsy, and short stature. The phenotypic spectrum is extremely diverse, with multisystemic organ involvement leading to isolated diabetes, deafness, renal tubulopathy, hypertrophic cardiomyopathy, and retinitis pigmentosa. In 80% of cases, the syndrome is associated with an AG transmission mutation (A3243G) in the tRNALeu gene of the mitochondrial DNA (mtDNA). We describe a woman with a unique combination of the MELAS A3243G mutation and multiple mtDNA deletions with normal POLG sequence. The patient presented with diabetes mellitus, sensorineural deafness, short stature, and mental disorientation. All her three children died in early adolescence.

Polymicrogyria and myoclonic epilepsy in autosomal recessive cutis laxa type 2A

Cutis laxa syndromes are rare inherited disorders of skin and connective tissue metabolism associated with variable systemic involvement. The main clinical manifestation is loose, wrinkled, redundant, inelastic skin, hypotonia, typical facies including short nose and down-slanting palpebral fissures, and varying degrees of developmental delay. The aim of this report is to describe two siblings diagnosed with a moderate form of ATP6V0A2-related cutis laxa with polymicrogyria (cobblestone-like brain dysgenesis). One of the patients has myoclonic epilepsy which may have contributed to his more severe clinical presentation. The literature on cutis laxa syndromes is reviewed.