Mutation Spectrum in the CACNA1A Gene in 49 Patients with Episodic Ataxia.

Episodic ataxia is an autosomal dominant ion channel disorder characterized by episodes of imbalance and incoordination. The disease is genetically heterogeneous and is classified as episodic ataxia type 2 (EA2) when it is caused by a mutation in the CACNA1A gene, encoding the α1A subunit of the P/Q-type voltage-gated calcium channel Cav2.1. The vast majority of EA2 disease-causing variants are loss-of-function (LoF) point changes leading to decreased channel currents. CACNA1A exonic deletions have also been reported in EA2 using quantitative approaches. We performed a mutational screening of the CACNA1A gene, including the promoter and 3'UTR regions, in 49 unrelated patients diagnosed with episodic ataxia. When pathogenic variants were not found by sequencing, we performed a copy number variant (CNV) analysis to screen for duplications or deletions. Overall, sequencing screening allowed identification of six different point variants (three nonsense and three missense changes) and two coding indels, one of them found in two unrelated patients. Additionally, CNV analysis identified a deletion in a patient spanning exon 35 as a result of a recombination event between flanking intronic Alu sequences. This study allowed identification of potentially pathogenic alterations in our sample, five of them novel, which cover 20% of the patients (10/49). Our data suggest that most of these variants are disease-causing, although functional studies are required.

Clinical and genetic analysis in alternating hemiplegia of childhood: ten new patients from Southern Europe.

Alternating hemiplegia of childhood (AHC) is a rare neurodevelopmental disorder featuring attacks of hemiplegia and other paroxysmal and non-paroxysmal manifestations leading to progressive neurological impairment. De novo mutations in ATP1A3 have been identified in up to 80% of patients. AHC is also associated with rare mutations in other genes involved in episodic neurological disorders. We sought to find mutations in ATP1A3, CACNA1A, ATP1A2, SCN1A and SLC2A1 in a cohort of ten unrelated patients from Spain and Greece. All patients fulfilled AHC diagnostic criteria. All five genes were amplified by PCR and Sanger sequenced. Copy number variation (CNV) analysis of SLC2A1 and CACNA1A was performed using two different approaches. We identified three previously described heterozygous missense ATP1A3 mutations (p.Asp801Asn, p.Glu815Lys and p.Gly947Arg) in five patients. No disease-causing mutations were found in the remaining genes. All mutations occurred de novo; carriers presented on average earlier than non-carriers. Intellectual disability was more severe with the p.Glu815Lys variant. A p.Gly947Arg carrier harbored a maternally-inherited CACNA1A p.Ala454Thr variant. Of note, three of our patients exhibited remarkable clinical responses to the ketogenic diet. We confirmed ATP1A3 mutations in half of our patients. Further AHC genetic studies will need to investigate large rearrangements in ATP1A3 or consider greater genetic heterogeneity than previously suspected.

Screening of CACNA1A and ATP1A2 genes in hemiplegic migraine: clinical, genetic, and functional studies.

Hemiplegic migraine (HM) is a rare and severe subtype of autosomal dominant migraine, characterized by a complex aura including some degree of motor weakness. Mutations in four genes (CACNA1A, ATP1A2, SCN1A and PRRT2) have been detected in familial and in sporadic cases. This genetically and clinically heterogeneous disorder is often accompanied by permanent ataxia, epileptic seizures, mental retardation, and chronic progressive cerebellar atrophy. Here we report a mutation screening in the CACNA1A and ATP1A2 genes in 18 patients with HM. Furthermore, intragenic copy number variant (CNV) analysis was performed in CACNA1A using quantitative approaches. We identified four previously described missense CACNA1A mutations (p.Ser218Leu, p.Thr501Met, p.Arg583Gln, and p.Thr666Met) and two missense changes in the ATP1A2 gene, the previously described p.Ala606Thr and the novel variant p.Glu825Lys. No structural variants were found. This genetic screening allowed the identification of more than 30% of the disease alleles, all present in a heterozygous state. Functional consequences of the CACNA1A-p.Thr501Met mutation, previously described only in association with episodic ataxia, and ATP1A2-p.Glu825Lys, were investigated by means of electrophysiological studies, cell viability assays or Western blot analysis. Our data suggest that both these variants are disease-causing.

A replication study of a GWAS finding in migraine does not identify association in a Spanish case-control sample.

BACKGROUND: Migraine is a prevalent neurological disorder with a complex genetic background characterized by recurrent episodes of headache. The disease is subclassified into migraine with aura (MA) and migraine without aura (MO). Many association studies have been performed to date to identify genetic risk variants for common migraine, most of them focusing on selected candidate genes, with variable and often inconsistent results. Recently, a clinic-based genome-wide association study for migraine reported a functionally relevant risk variant (SNP rs1835740), involved in glutamate homeostasis, which showed a significant association with MA. We aimed to replicate this finding in a clinic-based study of a Spanish cohort with MA and MO patients. METHODS: We genotyped SNP rs1835740 in a Spanish sample of 1521 patients and 1379 screened controls and performed a case-control association study. CONCLUSION: No association was found between the assayed SNP and any of the clinical groups considered.

SNP variants within the vanilloid TRPV1 and TRPV3 receptor genes are associated with migraine in the Spanish population.

The transient receptor potential (TRP) superfamily of non-selective cationic channels are involved in several processes plausibly relevant to migraine pathophysiology, including multimodal sensory and pain perception, central and peripheral sensitization, and regulation of calcium homeostasis. With the aim of identifying single nucleotide polymorphisms (SNPs) in TRP genes that may confer increased genetic susceptibility to migraine, we carried out a case-control genetic association study with replication, including a total of 1,040 cases and 1,037 controls. We genotyped 149 SNPs covering 14 TRP genes with known brain expression. The two-stage study comprised samples of 555 and 485 Spanish, Caucasian patients, selected according to the ICHD-II criteria for the diagnosis of migraine without aura (MO) or migraine with aura (MA). In the discovery sample, 19 SNPs in ten TRP genes showed nominal association (P < 0.05) with MO, MA, or overall migraine. In the replication sample, nominal association was confirmed for TRPV3 rs7217270 in MA and TRPV1 rs222741 in the overall migraine group. Risk haplotypes were identified for seven of the genes showing nominal association in the discovery set, but none of them was replicated. The present findings suggest that members of the vanilloid TRPV subfamily of receptors contribute to the genetic susceptibility to migraine in the Spanish population.

Acute striatal necrosis in hemiplegic migraine with de novo CACNA1A mutation.

We report the case of a 9-year-old girl with early-onset developmental delay, chronic ataxia and prolonged hemiplegic migraine episodes bringing about progressive deterioration. Two days into one episode, diffusion-weighted magnetic resonance imaging disclosed unilateral striatal abnormal signal consistent with cytotoxic edema, which evolved into atrophy on follow-up scans. Mutational screen of CACNA1A gene identified a de novo p.Tyr1387Cys mutation.

A mutation in the first intracellular loop of CACNA1A prevents P/Q channel modulation by SNARE proteins and lowers exocytosis.

Familial hemiplegic migraine (FHM)-causing mutations in the gene encoding the P/Q Ca(2+) channel alpha(1A) subunit (CACNA1A) locate to the pore and voltage sensor regions and normally involve gain-of-channel function. We now report on a mutation identified in the first intracellular loop of CACNA1A (alpha(1A(A454T))) that does not cause FHM but is associated with the absence of sensorimotor symptoms in a migraine with aura pedigree. Alpha(1A(A454T)) channels showed weakened regulation of voltage-dependent steady-state inactivation by Ca(V)beta subunits. More interestingly, A454T mutation suppressed P/Q channel modulation by syntaxin 1A or SNAP-25 and decreased exocytosis. Our findings reveal the importance of I-II loop structural integrity in the functional interaction between P/Q channel and proteins of the vesicle-docking/fusion machinery, and that genetic variation in CACNA1A may be not only a cause but also a modifier of migraine phenotype.