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Tomlinson SE, Tan SV, Burke D, Labrum RW, Haworth A, Gibbons VS, Sweeney MG, Griggs RC, Kullmann DM, Bostock H, Hanna MG. In vivo impact of presynaptic calcium channel dysfunction on motor axons in episodic ataxia type 2. Brain 2016; 139:380-91. [PMID: 26912519 PMCID: PMC4795516 DOI: 10.1093/brain/awv380] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 10/22/2015] [Accepted: 10/26/2015] [Indexed: 11/13/2022] Open
Abstract
Ion channel dysfunction causes a range of neurological disorders by altering transmembrane ion fluxes, neuronal or muscle excitability, and neurotransmitter release. Genetic neuronal channelopathies affecting peripheral axons provide a unique opportunity to examine the impact of dysfunction of a single channel subtype in detail in vivo. Episodic ataxia type 2 is caused by mutations in CACNA1A, which encodes the pore-forming subunit of the neuronal voltage-gated calcium channel Cav2.1. In peripheral motor axons, this channel is highly expressed at the presynaptic neuromuscular junction where it contributes to action potential-evoked neurotransmitter release, but it is not expressed mid-axon or thought to contribute to action potential generation. Eight patients from five families with genetically confirmed episodic ataxia type 2 underwent neurophysiological assessment to determine whether axonal excitability was normal and, if not, whether changes could be explained by Cav2.1 dysfunction. New mutations in the CACNA1A gene were identified in two families. Nerve conduction studies were normal, but increased jitter in single-fibre EMG studies indicated unstable neuromuscular transmission in two patients. Excitability properties of median motor axons were compared with those in 30 age-matched healthy control subjects. All patients had similar excitability abnormalities, including a high electrical threshold and increased responses to hyperpolarizing (P < 0.00007) and depolarizing currents (P < 0.001) in threshold electrotonus. In the recovery cycle, refractoriness (P < 0.0002) and superexcitability (P < 0.006) were increased. Cav2.1 dysfunction in episodic ataxia type 2 thus has unexpected effects on axon excitability, which may reflect an indirect effect of abnormal calcium current fluxes during development.
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Affiliation(s)
- Susan E Tomlinson
- 1 Sydney Medical School, University of Sydney, Australia 2 Department of Neurology, St Vincent's Hospital, Sydney, Australia
| | - S Veronica Tan
- 3 Institute of Neurology, University College London and MRC Centre for Neuromuscular Disease, Queen Square, UK
| | - David Burke
- 1 Sydney Medical School, University of Sydney, Australia 4 Department of Neurology, Royal Prince Alfred Hospital, Sydney, Australia
| | - Robyn W Labrum
- 5 Neurogenetics Unit, National Hospital for Neurology, Queen Square, UK
| | - Andrea Haworth
- 5 Neurogenetics Unit, National Hospital for Neurology, Queen Square, UK
| | | | - Mary G Sweeney
- 5 Neurogenetics Unit, National Hospital for Neurology, Queen Square, UK
| | | | - Dimitri M Kullmann
- 3 Institute of Neurology, University College London and MRC Centre for Neuromuscular Disease, Queen Square, UK 5 Neurogenetics Unit, National Hospital for Neurology, Queen Square, UK
| | - Hugh Bostock
- 3 Institute of Neurology, University College London and MRC Centre for Neuromuscular Disease, Queen Square, UK
| | - Michael G Hanna
- 3 Institute of Neurology, University College London and MRC Centre for Neuromuscular Disease, Queen Square, UK 5 Neurogenetics Unit, National Hospital for Neurology, Queen Square, UK
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Tomlinson SE, Rajakulendran S, Tan SV, Graves TD, Bamiou DE, Labrum RW, Burke D, Sue CM, Giunti P, Schorge S, Kullmann DM, Hanna MG. Clinical, genetic, neurophysiological and functional study of new mutations in episodic ataxia type 1. J Neurol Neurosurg Psychiatry 2013; 84:1107-12. [PMID: 23349320 PMCID: PMC4332158 DOI: 10.1136/jnnp-2012-304131] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
BACKGROUND AND OBJECTIVE Heterozygous mutations in KCNA1 cause episodic ataxia type 1 (EA1), an ion channel disorder characterised by brief paroxysms of cerebellar dysfunction and persistent neuromyotonia. This paper describes four previously unreported families with EA1, with the aim of understanding the phenotypic spectrum associated with different mutations. METHODS 15 affected individuals from four families underwent clinical, genetic and neurophysiological evaluation. The functional impact of new mutations identified in the KCNA1 gene was investigated with in vitro electrophysiology and immunocytochemistry. RESULTS Detailed clinical documentation, dating back to 1928 in one family, indicates that all patients manifested episodic ataxia of varying severity. Four subjects from three families reported hearing impairment, which has not previously been reported in association with EA1. New mutations (R167M, C185W and I407M) were identified in three out of the four families. When expressed in human embryonic kidney cells, all three new mutations resulted in a loss of K(v)1.1 channel function. The fourth family harboured a previously reported A242P mutation, which has not been previously described in association with ataxia. CONCLUSIONS The genetic basis of EA1 in four families is established and this report presents the earliest documented case from 1928. All three new mutations caused a loss of K(v)1.1 channel function. The finding of deafness in four individuals raises the possibility of a link between K(v)1.1 dysfunction and hearing impairment. Our findings broaden the phenotypic range associated with mutations in KCNA1.
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Catarino CB, Liu JYW, Liagkouras I, Gibbons VS, Labrum RW, Ellis R, Woodward C, Davis MB, Smith SJ, Cross JH, Appleton RE, Yendle SC, McMahon JM, Bellows ST, Jacques TS, Zuberi SM, Koepp MJ, Martinian L, Scheffer IE, Thom M, Sisodiya SM. Dravet syndrome as epileptic encephalopathy: evidence from long-term course and neuropathology. Brain 2011; 134:2982-3010. [PMID: 21719429 PMCID: PMC3187538 DOI: 10.1093/brain/awr129] [Citation(s) in RCA: 150] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Dravet syndrome is an epilepsy syndrome of infantile onset, frequently caused by SCN1A mutations or deletions. Its prevalence, long-term evolution in adults and neuropathology are not well known. We identified a series of 22 adult patients, including three adult post-mortem cases with Dravet syndrome. For all patients, we reviewed the clinical history, seizure types and frequency, antiepileptic drugs, cognitive, social and functional outcome and results of investigations. A systematic neuropathology study was performed, with post-mortem material from three adult cases with Dravet syndrome, in comparison with controls and a range of relevant paediatric tissue. Twenty-two adults with Dravet syndrome, 10 female, were included, median age 39 years (range 20-66). SCN1A structural variation was found in 60% of the adult Dravet patients tested, including one post-mortem case with DNA extracted from brain tissue. Novel mutations were described for 11 adult patients; one patient had three SCN1A mutations. Features of Dravet syndrome in adulthood include multiple seizure types despite polytherapy, and age-dependent evolution in seizure semiology and electroencephalographic pattern. Fever sensitivity persisted through adulthood in 11 cases. Neurological decline occurred in adulthood with cognitive and motor deterioration. Dysphagia may develop in or after the fourth decade of life, leading to significant morbidity, or death. The correct diagnosis at an older age made an impact at several levels. Treatment changes improved seizure control even after years of drug resistance in all three cases with sufficient follow-up after drug changes were instituted; better control led to significant improvement in cognitive performance and quality of life in adulthood in two cases. There was no histopathological hallmark feature of Dravet syndrome in this series. Strikingly, there was remarkable preservation of neurons and interneurons in the neocortex and hippocampi of Dravet adult post-mortem cases. Our study provides evidence that Dravet syndrome is at least in part an epileptic encephalopathy.
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Affiliation(s)
- Claudia B Catarino
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology and National Hospital for Neurology and Neurosurgery, UCL, Queen Square, London WC1N 3BG, UK
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Rajakulendran S, Graves TD, Labrum RW, Kotzadimitriou D, Eunson L, Davis MB, Davies R, Wood NW, Kullmann DM, Hanna MG, Schorge S. Genetic and functional characterisation of the P/Q calcium channel in episodic ataxia with epilepsy. J Physiol 2010; 588:1905-13. [PMID: 20156848 DOI: 10.1113/jphysiol.2009.186437] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Mutations in CACNA1A, which encodes the principal subunit of the P/Q calcium channel, underlie episodic ataxia type 2 (EA2). In addition, some patients with episodic ataxia complicated by epilepsy have been shown to harbour CACNA1A mutations, raising the possibility that P/Q channel dysfunction may be linked to human epilepsy. We undertook a review of all published CACNA1A EA2 cases and this showed that 7% have epilepsy--representing a sevenfold increased epilepsy risk compared to the background population risk (P<0.001). We also studied a series of 17 individuals with episodic ataxia accompanied by epilepsy and/or clearly epileptiform electroencephalograms (EEGs). We screened the entire coding region of CACNA1A for point mutations and rearrangements to determine if genetic variation in the gene is associated with the epilepsy phenotype, and measured the functional impact of all missense variations on heterologously expressed P/Q channels. We identified two large scale deletions and two new missense mutations in CACNA1A. When expressed, L621R had little detectable effect on P/Q channel function, while the other missense change, G540R, caused an approximately 30% reduction in current density. In nine patients we also identified the previously reported non-synonymous coding variants (E921D and E993V) which also resulted in impairment of P/Q channel function. Taken together, 12 of the 17 patients have genetic changes which decrease P/Q channel function. We conclude that variants in the coding region of CACNA1A that confer a loss of P/Q-type channel function are associated with episodic ataxia and epilepsy. Our data suggest that functional stratification of all variants, including common polymorphisms, rare variants and novel mutations, may provide new insights into the mechanisms of channelopathies.
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Affiliation(s)
- Sanjeev Rajakulendran
- MRC Centre for Neuromuscular Diseases, Department of Molecular Neuroscience, University College London, Institute of Neurology, London WC1N 3BG, UK
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Labrum RW, Rajakulendran S, Graves TD, Eunson LH, Bevan R, Sweeney MG, Hammans SR, Tubridy N, Britton T, Carr LJ, Ostergaard JR, Kennedy CR, Al-Memar A, Kullmann DM, Schorge S, Temple K, Davis MB, Hanna MG. Large scale calcium channel gene rearrangements in episodic ataxia and hemiplegic migraine: implications for diagnostic testing. J Med Genet 2009; 46:786-91. [PMID: 19586927 DOI: 10.1136/jmg.2009.067967] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
BACKGROUND Episodic ataxia type 2 (EA2) and familial hemiplegic migraine type 1 (FHM1) are autosomal dominant disorders characterised by paroxysmal ataxia and migraine, respectively. Point mutations in CACNA1A, which encodes the neuronal P/Q-type calcium channel, have been detected in many cases of EA2 and FHM1. The genetic basis of typical cases without CACNA1A point mutations is not fully known. Standard DNA sequencing methods may miss large scale genetic rearrangements such as deletions and duplications. The authors investigated whether large scale genetic rearrangements in CACNA1A can cause EA2 and FHM1. METHODS The authors used multiplex ligation dependent probe amplification (MLPA) to screen for intragenic CACNA1A rearrangements. RESULTS The authors identified five previously unreported large scale deletions in CACNA1A in seven families with episodic ataxia and in one case with hemiplegic migraine. One of the deletions (exon 6 of CACNA1A) segregated with episodic ataxia in a four generation family with eight affected individuals previously mapped to 19p13. In addition, the authors identified the first pathogenic duplication in CACNA1A in an index case with isolated episodic diplopia without ataxia and in a first degree relative with episodic ataxia. CONCLUSIONS Large scale deletions and duplications can cause CACNA1A associated channelopathies. Direct DNA sequencing alone is not sufficient as a diagnostic screening test.
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Affiliation(s)
- R W Labrum
- MRC Centre for Neuromuscular Diseases, Institute of Neurology, UCL, London WC1N 3BG, UK
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