Early onset, non fluctuating spinocerebellar ataxia and a novel missense mutation in CACNA1A gene

doi:10.1016/j.jns.2005.10.007

Journal of the Neurological Sciences

Volume 241, Issues 1–2, 15 February 2006, Pages 13-17

https://doi.org/10.1016/j.jns.2005.10.007 Get rights and content

Abstract

Mutations in the brain-specific P/Q type Ca²⁺ channel α1 subunit gene, CACNA1A, have been identified in three clinically distinct disorders, spinocerebellar ataxia type 6 (SCA6), episodic ataxia type 2 (EA2), and familial hemiplegic migraine type 1 (FHM1). SCA6 is associated with small expansions of a CAG repeat at the 3′ end of the gene, while point mutations are mostly responsible for its two allelic disorders, FHMI and EA2. From the electrophysiological point of view, while FHMI mutations lead to a gain of function [Tottene A, Fellin T, Pagnutti S, Luvisetto S, Striessnig J, Fletcher C, et al. Familial hemiplegic migraine mutations increase Ca(2+) influx through single human CaV2.1 channels and decrease maximal CaV2.1 current density in neurons. Proc Natl Acad Sci 99 (20) (2002) 13284–13289.], EA2 mutations usually generate a loss of channel function [Guida S, Trettel F, Pagnutti S, Mantuano E, Tottene A, Veneziano L, et al. Complete loss of P/Q calcium channel activity caused by a CACNA1A missense mutation carried by patients with episodic ataxia type 2. Am J Hum Genet 68 (3) (2001) 759–764, Wappl E, Koschak A, Poteser M, Sinnegger MJ, Walter D, Eberhart A, et al. Functional consequences of P/Q-type Ca²⁺ channel Cav2.1 missense mutations associated with episodic ataxia type 2 and progressive ataxia. J Biol Chem 277 (9) (2002) 6960–6966.]. In the present study, we describe a child affected by permanent non-fluctuating limb and trunk ataxia with a quite early age of onset. Interestingly, the size of the CACNA1A triplet repeat region in the patient is within the normal range while he carries a novel de novo missense mutation in this gene, p.R1664Q. Although functional data are not available, based on the literature data indicating that severe reductions in P/Q-type channel activity favour episodic and/or progressive ataxic symptoms [Wappl E, Koschak A, Poteser M, Sinnegger MJ, Walter D, Eberhart A, et al. Functional consequences of P/Q-type Ca²⁺ channel Cav2.1 missense mutations associated with episodic ataxia type 2 and progressive ataxia. J Biol Chem 2002;277(9):6960–6966.], we hypothesize that the functional consequence of the mutation here identified is a partial loss of the Ca channel function. In conclusion, the clinical and molecular findings reported here suggest the opportunity to screen for point mutation in this gene, even patients with a clinical phenotype for some aspects slightly different from the typical picture more commonly associated to SCA6, EA2 or FHM1 diseases.

Introduction

The CACNA1A gene encodes the pore forming subunit of the main transmembrane neuronal (P/Q type) voltage-gated Ca²⁺ channels [4]. Each subunit consists of four domains (repeats) of six transmembrane segments (S1–S6) connected by intracellular loops. Mutations in this gene cause at least three dominantly inherited neurological disorders with overlapping clinical features, the progressive spinocerebellar ataxia, SCA6 [5], familial hemiplegic migraine type I (FHMI) and episodic ataxia type 2(EA2) [6]. SCA6 is associated with small expansions of a CAG repeat at the 3′ end of the gene, while point mutations are responsible for its two allelic disorders, FHMI (mostly missense mutations) and EA2 pure or associated to other neurologic deficit such as interictal dystonia, seizures or cognitive impairment (both nonsense and splicing mutations) (reviewed in Jen et al. [7]). Families displaying more complex phenotypes including variable combinations of episodic and progressive ataxia in different affected members and carrying either CAG triplet expansion or point mutation in CACNA1A have also been described [8], [9], [10].

Here, we report a novel CACNA1A missense mutation in a patient with not fluctuating ataxia with a quite early age of onset.

Section snippets

Patient

We describe a child who came to our attention at 14 months of age because of unbalanced gait and impossibility to walk more than 3–4 steps without falls. This first neurological examination revealed ataxia, clumsiness, mild axial hypotonia, well-coordinated upper extremities, and absence of tremor. Pain and touch senses were unimpaired. No dysmorphic features were observed. No family history for neurological diseases, uneventful pregnancy and delivery and regular neonatal period were reported.

Mutation analysis

The proband was first checked for the presence of a CAG triplet expansion within the 3′ end of CACNA1A gene. He resulted to be heterozygous for two alleles with 14 and 12 triplets, respectively, and therefore within the normal range. Then, direct sequencing of all exons of CACNA1A gene amplified from the proband genomic DNA, revealed a heterozygous base change at position c.4991G > A of the cDNA. This nucleotide change leads to the replacement of an arginine by a glutamine in position 1664 of the

Discussion

The patient we describe here has non-fluctuating limb and trunk ataxia, a clinical picture similar to what has been reported for SCA6. Nevertheless, some atypical features can also be observed such as a quite early age of onset and mild motor developmental delay that are not commonly associated to a SCA6 phenotype. In addition to that, the patient carries a novel de novo missense mutation in CACNA1A gene, a type of mutation more commonly associated to episodic ataxia type 2 (EA2) and to FHMI

Acknowledgements

The study was supported by funds from the Italian ministry of Health, RC2005. The authors wish to thank the patient's family for their cooperation and Daniela Galbiati for technical assistance.

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There are more references available in the full text version of this article.

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2021, European Journal of Paediatric Neurology
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One variant, published by Bahamonde et al. as a GOF [17] variant, showed that a single amino acid deletion (ΔF1502) in the S6 Segment of CaV2.1 Domain III associated with congenital ataxia increases channel activity and promotes Ca2+ influx. Eleven variants were defined as LOF variants and one variant was hypothesized by Tonelli to be a LOF variant [18] The other 10 were nonsense variants (stop codons, splicing and frameshift). In our cohort, all nine patients with epilepsy had untested variants; LOF variants were found in five out of seventeen patients with EA, four out of fourteen patients with migraines, and two patients who had PNEEs and became free of symptoms after the age of two years.
CACNA1A-related disorders present with persistent progressive and non-progressive cerebellar ataxia and paroxysmal events: epileptic seizures and non-epileptic attacks. These phenotypes overlap and co-exist in the majority of patients.
To describe phenotypes in infantile onset CACNA1A-related disorder and to explore intra-familial variations and genotype-phenotype correlations.
This study was a multicenter international collaboration. A retrospective chart review of CACNA1A patients was performed. Clinical, radiological, and genetic data were collected and analyzed in 47 patients with infantile-onset disorder.
Paroxysmal non-epileptic events (PNEE) were observed in 68% of infants, with paroxysmal tonic upward gaze (PTU) noticed in 47% of infants. Congenital cerebellar ataxia (CCA) was diagnosed in 51% of patients including four patients with developmental delay and only one neurological sign. PNEEs were found in 63% of patients at follow-up, with episodic ataxia (EA) in 40% of the sample. Cerebellar ataxia was found in 58% of the patients at follow-up. Four patients had epilepsy in infancy and nine in childhood. Seven infants had febrile convulsions, three of which developed epilepsy later; all three patients had CCA. Cognitive difficulties were demonstrated in 70% of the children. Cerebellar atrophy was found in only one infant but was depicted in 64% of MRIs after age two.
Nearly all of the infants had CCA, PNEE or both. Cognitive difficulties were frequent and appeared to be associated with CCA. Epilepsy was more frequent after age two. Febrile convulsions in association with CCA may indicate risk of epilepsy in later childhood. Brain MRI was normal in infancy. There were no genotype-phenotype correlations found.
Spinocerebellar ataxias
2018, Handbook of Clinical Neurology
Citation Excerpt :
When expressed as an independent polypeptide, α1ACT – bearing an expanded polyQ tract – lacks transcription factor function and neurite outgrowth properties, causes cell death in culture, and leads to ataxia and cerebellar atrophy in transgenic mice (Du et al., 2013). The allelic disorder, ADCAs associated with CACNA1A mutations (including p.Gly293Arg in the P loop of the first domain, p.Ala454Thr in the I-II loop, and p.Arg1664Gln), has a very similar phenotype to that of SCA6 associated with CAG repeat expansions (Yue et al., 1997; Tonelli et al., 2006; Cricchi et al., 2007). The CAG repeats range from (CAG)4 to (CAG)18 in normal alleles.
There are over 40 autosomal dominant spinocerebellar ataxias (SCAs) now identified. In this chapter we delineate the phenotypes of SCAs 1-44 and dentatorubral-pallidoluysian atrophy (DRPLA) and highlight the clinical and genetic features of the well characterised SCAs in detail in the main section of the chapter, along with their frequency and age at onset. We have included a section on the key phenotypic features of rare spinocerebellar ataxias and discuss rare and unusual presentations and genetic mechanisms of the ataxias and show differences between adult and paediatric presentations. We look at unusual mechanisms where knowledge is evolving in some dominant ataxias. For ease of reference we have tabulated historical aspects of the ataxias, major neurological diagnostic features, ataxias with predominant paediatric and infantile onset and list recognisable nerve conduction features. We comment on the anti-sense ataxia gene mechanisms and we discuss potential developments including exome sequencing and potential therapeutic options. A gene table listing all of the identified SCAs and DRPLA is also included with key references and gene locations and symbols with OMIM reference numbers for further reading.
Whole Exome Sequencing and Heterologous Cellular Electrophysiology Studies Elucidate a Novel Loss-of-Function Mutation in the CACNA1A-Encoded Neuronal P/Q-Type Calcium Channel in a Child with Congenital Hypotonia and Developmental Delay
2016, Pediatric Neurology
Citation Excerpt :
These findings, in combination with the mouse wobbly mutant and phenotype, the previous case report with the de novo p.R1349Q variant, and the de novo p.P1353L loss-of-function variant observed in our patient, provide evidence that the p.P1353L mutation is likely responsible for the phenotypes observed in our patient, and additionally provides evidence that this entire transmembrane domain may be essential for protein function. The array of phenotypes among CACNA1A-related diseases is also demonstrated by the variety of novel phenotypes secondary to de novo mutations in CACNA1A, including early-onset, nonfluctuating spinocerebellar ataxia,36 intellectual disability, congenital ataxia, and dyskinesia.22 Although these and other observations merit CACNA1A mutation analysis in cases of ataxia, recurrent hemiparesis, or coma,22 the early-onset hypotonia with developmental delay seen in our patient represents a novel presentation associated with a CACNA1A mutation.
A 4-year-old boy born at 37 weeks' gestation with intrauterine growth retardation presented with developmental delay with pronounced language and gross motor delay, axial hypotonia, and dynamic hypertonia of the extremities. Investigations including the Minnesota Newborn Screen, thyroid stimulating hormone/thyroxin, and inborn errors of metabolism screening were negative. Cerebral magnetic resonance imaging and spectroscopy were normal. Genetic testing was negative for coagulopathy, Smith-Lemli-Opitz, fragile X, and Prader-Willi/Angelman syndromes. Whole genome array analysis was unremarkable.
Whole exome sequencing was performed through a commercial testing laboratory to elucidate the underlying etiology for the child's presentation. A de novo mutation was hypothesized. In attempt to establish pathogenicity of our candidate variant, cellular electrophysiologic functional analysis of the putative de novo mutation was performed using patch-clamp technology.
Whole exome sequencing revealed a p.P1353L variant in the CACNA1A gene, which encodes for the α1-subunit of the brain-specific P/Q-type calcium channel (Ca_V2.1). This presynaptic high-voltage-gated channel couples neuronal excitation to the vesicular release of neurotransmitter and is implicated in several neurologic disorders. DNA Sanger sequencing confirmed that the de novo mutation was absent in both parents and present in the child only. Electrophysiologic analysis of P1353L-CACNA1A demonstrated near complete loss of function, with a 95% reduction in peak current density.
Whole exome sequencing coupled with cellular electrophysiologic functional analysis of a de novo CACNA1A missense mutation has elucidated the probable underlying pathophysiologic mechanism responsible for the child's phenotype. Genetic testing of CACNA1A in patients with congenital hypotonia and developmental delay may be warranted.
Congenital ataxia and hemiplegic migraine with cerebral edema associated with a novel gain of function mutation in the calcium channel CACNA1A
2014, Journal of the Neurological Sciences
Citation Excerpt :
Most EA2 patients have a progressive cerebellar syndrome and cerebellar atrophy predominating on the anterior vermis [13]. Onset as early as 14 months and absence of fluctuations have been reported [16]. The majority of the CACNA1A mutations associated to EA2 are nonsense mutations or deletions and/or insertions that disrupt the open reading frame leading to the truncation of the protein or are intronic mutations that also presumably disrupt the reading frame.
Mutations in the CACNA1A gene, encoding the α1 subunit of the voltage-gated calcium channel Ca_V2.1 (P/Q-type), have been associated with three neurological phenotypes: familial and sporadic hemiplegic migraine type 1 (FHM1, SHM1), episodic ataxia type 2 (EA2), and spinocerebellar ataxia type 6 (SCA6). We report a child with congenital ataxia, abnormal eye movements and developmental delay who presented severe attacks of hemiplegic migraine triggered by minor head traumas and associated with hemispheric swelling and seizures. Progressive cerebellar atrophy was also observed. Remission of the attacks was obtained with acetazolamide. A de novo 3 bp deletion was found in heterozygosity causing loss of a phenylalanine residue at position 1502, in one of the critical transmembrane domains of the protein contributing to the inner part of the pore. We characterized the electrophysiology of this mutant in a Xenopus oocyte in vitro system and showed that it causes gain of function of the channel. The mutant Ca_V2.1 activates at lower voltage threshold than the wild type. These findings provide further evidence of this molecular mechanism as causative of FHM1 and expand the phenotypic spectrum of CACNA1A mutations with a child exhibiting severe SHM1 and non-episodic ataxia of congenital onset.
A novel missense mutation in CACNA1A evaluated by in silico protein modeling is associated with non-episodic spinocerebellar ataxia with slow progression
2014, European Journal of Medical Genetics
Citation Excerpt :
On the other hand, FHM1 mutation carriers may develop cerebellar symptoms with or without concomitant hemiplegic migraine [Yabe et al., 2008]. Several other mutations have been identified in a chronic progressive cerebellar syndrome [Alonso et al., 2004; Blumkin et al., 2010; Marti et al., 2008; Romaniello et al., 2010; Tonelli et al., 2006; Wada et al., 2002; Wan et al., 2005; Yue et al., 1997]. Here, we describe three families presenting with slow progressive cerebellar ataxia associated with distinct missense exchanges affecting highly conserved regions of CACNA1A.
Spinocerebellar ataxia type 6 (SCA6), episodic ataxia type 2 (EA2) and familial hemiplegic migraine type 1 (FHM1) are allelic disorders of the gene CACNA1A encoding the P/Q subunit of a voltage gated calcium channel. While SCA6 is related to repeat expansions affecting the C-terminal part of the protein, EA2 and FHM phenotypes are usually associated with nonsense and missense mutations leading to impaired channel properties.
In three unrelated families with dominant cerebellar ataxia, symptoms cosegregated with CACNA1A missense mutations of evolutionary highly conserved amino acids (exchanges p.E668K, p.R583Q and p.D302N). To evaluate pathogenic effects, in silico, protein modeling analyses were performed which indicate structural alterations of the novel mutation p.E668K within the homologous domain 2 affecting CACNA1A protein function. The phenotype is characterised by a very slowly progressive ataxia, while ataxic episodes or migraine are uncommon. These findings enlarge the phenotypic spectrum of CACNA1A mutations.
Clinically severe CACNA1A alleles affect synaptic function and neurodegeneration differentially
2017, PLoS Genetics
Dominant mutations in CACNA1A, encoding the α-1A subunit of the neuronal P/Q type voltage-dependent Ca²⁺ channel, can cause diverse neurological phenotypes. Rare cases of markedly severe early onset developmental delay and congenital ataxia can be due to de novo CACNA1A missense alleles, with variants affecting the S4 transmembrane segments of the channel, some of which are reported to be loss-of-function. Exome sequencing in five individuals with severe early onset ataxia identified one novel variant (p.R1673P), in a girl with global developmental delay and progressive cerebellar atrophy, and a recurrent, de novo p.R1664Q variant, in four individuals with global developmental delay, hypotonia, and ophthalmologic abnormalities. Given the severity of these phenotypes we explored their functional impact in Drosophila. We previously generated null and partial loss-of-function alleles of cac, the homolog of CACNA1A in Drosophila. Here, we created transgenic wild type and mutant genomic rescue constructs with the two noted conserved point mutations. The p.R1673P mutant failed to rescue cac lethality, displayed a gain-of-function phenotype in electroretinograms (ERG) recorded from mutant clones, and evolved a neurodegenerative phenotype in aging flies, based on ERGs and transmission electron microscopy. In contrast, the p.R1664Q variant exhibited loss of function and failed to develop a neurodegenerative phenotype. Hence, the novel R1673P allele produces neurodegenerative phenotypes in flies and human, likely due to a toxic gain of function.

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¹: The authors contributed equally to this work.

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Journal of the Neurological Sciences

Abstract

Introduction

Section snippets

Patient

Mutation analysis

Discussion

Acknowledgements

References (20)

Complete loss of P/Q calcium channel activity caused by a CACNA1A missense mutation carried by patients with episodic ataxia type 2

Am J Hum Genet

Functional consequences of P/Q-type Ca²⁺ channel Cav2.1 missense mutations associated with episodic ataxia type 2 and progressive ataxia

J Biol Chem

Familial hemiplegic migraine and episodic ataxia type-2 are caused by mutations in the Ca²⁺ channel gene CACNL1A4

Cell

Progressive ataxia due to a missense mutation in a calcium-channel gene

Am J Hum Genet

Voltage-gated ion channels and electrical excitability

Neuron

Three new familial hemiplegic migraine mutants affect P/Q-type Ca(2+) channel kinetics

J Biol Chem

Familial hemiplegic migraine mutations increase Ca(2+) influx through single human CaV2.1 channels and decrease maximal CaV2.1 current density in neurons

Proc Natl Acad Sci

Primary structure and functional expression from complementary DNA of a brain calcium channel

Nature

Autosomal dominant cerebellar ataxia (SCA6) associated with small polyglutamine expansions in the alpha 1A-voltage-dependent calcium channel

Nat Genet

Clinical spectrum of episodic ataxia type 2

Neurology

Cited by (39)

Clinical phenotypes of infantile onset CACNA1A-related disorder

Spinocerebellar ataxias

Whole Exome Sequencing and Heterologous Cellular Electrophysiology Studies Elucidate a Novel Loss-of-Function Mutation in the CACNA1A-Encoded Neuronal P/Q-Type Calcium Channel in a Child with Congenital Hypotonia and Developmental Delay

Congenital ataxia and hemiplegic migraine with cerebral edema associated with a novel gain of function mutation in the calcium channel CACNA1A

A novel missense mutation in CACNA1A evaluated by in silico protein modeling is associated with non-episodic spinocerebellar ataxia with slow progression

Clinically severe CACNA1A alleles affect synaptic function and neurodegeneration differentially