Dysfunction of the CaV2.1 calcium channel in cerebellar ataxias

Mutations in the CACNA1A gene are associated with episodic ataxia type 2 (EA2) and spinocerebellar ataxia type 6 (SCA6). CACNA1A encodes the α-subunit of the P/Q-type calcium channel or CaV2.1, which is highly enriched in the cerebellum. It is one of the main channels linked to synaptic transmission throughout the human central nervous system. Here, we compare recent advances in the understanding of the genetic changes that underlie EA2 and SCA6 and what these new findings suggest about the mechanism of the disease

Thinning of the Corpus Callosum and Cerebellar Atrophy is Correlated with Phenotypic Severity in a Family with Spastic Paraplegia Type 11

Background Mutations in the spatacsin gene are associated with spastic paraplegia type 11 (SPG11), which is the most-common cause of autosomal recessive hereditary spastic paraplegia. Although SPG11 has diverse phenotypes, thinning of the corpus callosum is an important feature.Case Report Clinical, genetic, and radiological evaluations were undertaken in a large family from Gujarat in North India with hereditary spastic paraplegia, whose affected members presented with varying degrees of spasticity, ataxia, and cognitive impairment. The clinical severity and the degree of corpus callosum and cerebellar atrophy varied among the four affected individuals in the family. Genetic testing of the affected members revealed recessive mutations in the spatacsin gene, consistent with a diagnosis of SPG11.Conclusions We believe that the extent of corpus callosum thinning and cerebellar atrophy is correlated with disease severity in affected patients. The addition of extrapyramidal features in the most-affected members suggests that SPG11 exhibits considerable phenotypic heterogeneity. J Clin Neurol 2011;7:102-10

Retention of brivaracetam in adults with drug-resistant epilepsy at a single tertiary care center

INTRODUCTION: Brivaracetam (BRV) is licensed as an adjunctive treatment for focal epilepsy. We describe our clinical experience with BRV at a large UK tertiary center. METHODS: Adults initiated on BRV between July 2015 and July 2020 were followed up until they discontinued BRV or September 2021. Data on epilepsy syndrome, duration, seizure types, concomitant and previous antiseizure medication (ASM) use, BRV dosing, efficacy, and side effects were recorded. Efficacy was categorized as temporary (minimum three months) or ongoing (at last follow-up) seizure freedom, ≥50% seizure reduction, or other benefits (e.g., no convulsions or daytime seizures). Brivaracetam retention was estimated using Kaplan-Meier survival analysis. RESULTS: Two-hundred people were treated with BRV, of whom 81% had focal epilepsy. The mean (interquartile range [IQR]) follow-up time was 707 (688) days, and the dose range was 50-600 mg daily. The mean (IQR) of the previous number of used ASMs was 6.9 (6.0), and concomitant use was 2.2 (1.0). One-hundred and eighty-eight people (94%) had previously discontinued levetiracetam (LEV), mainly due to side effects. 13/200 (6.5%) were seizure free for a minimum of six months during treatment, and 46/200 (23%) had a ≥50% reduction in seizure frequency for six months or more. Retention rates were 83% at six months, 71% at 12 months, and 57% at 36 months. Brivaracetam was mostly discontinued due to side effects (38/75, 51%) or lack of efficacy (28/75, 37%). Concomitant use of carbamazepine significantly increased the hazard ratio of discontinuing BRV due to side effects (p = 0.006). The most commonly reported side effects were low mood (20.5%), fatigue (18%) and aggressive behavior (8.5%). These side effects were less prevalent than when the same individuals took LEV (low mood, 59%; aggressive behavior, 43%). Intellectual disability was a risk factor for behavioral side effects (p = 0.004), and a pre-existing mood disorder significantly increased the likelihood of further episodes of low mood (p = 0.019). CONCLUSIONS: Brivaracetam was effective at a broad range of doses in managing drug-resistant epilepsy across various phenotypes, but less effective than LEV in those who switched due to poor tolerability on LEV. There were no new tolerability issues, but 77% of the individuals experiencing side effects on BRV also experienced similar side effects on LEV

Candidate Screening of the TRPC3 Gene in Cerebellar Ataxia

The hereditary cerebellar ataxias are a diverse group of neurodegenerative disorders primarily characterised by loss of balance and coordination due to dysfunction of the cerebellum and its associated pathways. Although many genetic mutations causing inherited cerebellar ataxia have been identified, a significant percentage of patients remain whose cause is unknown. The transient receptor potential (TRP) family member TRPC3 is a non-selective cation channel linked to key signalling pathways that are affected in cerebellar ataxia. Furthermore, genetic mouse models of TRPC3 dysfunction display cerebellar ataxia, making the TRPC3 gene an excellent candidate for screening ataxic patients with unknown genetic aetiology. Here, we report a genetic screen for TRPC3 mutations in a cohort of 98 patients with genetically undefined late-onset cerebellar ataxia and further ten patients with undefined episodic ataxia. We identified a number of variants but no causative mutations in TRPC3. Our findings suggest that mutations in TRPC3 do not significantly contribute to the cause of late-onset and episodic human cerebellar ataxias

Episodic ataxia type 1 mutations differentially affect neuronal excitability and transmitter release

Heterozygous mutations of KCNA1, the gene encoding potassium channel Kv1.1 subunits, cause episodic ataxia type 1 (EA1), which is characterized by paroxysmal cerebellar incoordination and interictal myokymia. Some mutations are also associated with epilepsy. Although Kv1.1-containing potassium channels play important roles in neuronal excitability and neurotransmitter release, it is not known how mutations associated with different clinical features affect the input-output relationships of individual neurons. We transduced rat hippocampal neurons, which were cultured on glial micro-islands, with lentiviruses expressing wild-type or mutant human KCNA1, and injected either depolarizing currents to evoke action potentials or depolarizing voltage commands to evoke autaptic currents. α-Dendrotoxin and tetraethylammonium allowed a pharmacological dissection of potassium currents underlying excitability and neurotransmission. Overexpression of wild-type Kv1.1 decreased both neuronal excitability and neurotransmitter release. By contrast, the C-terminus-truncated R417stop mutant, which is associated with severe drug-resistant EA1, had the opposite effect: increased excitability and release probability. Another mutant, T226R, which is associated with EA1 that is complicated by contractures and epilepsy, had no detectable effect on neuronal excitability; however, in common with R417stop, it markedly enhanced neurotransmitter release. The results provide direct evidence that EA1 mutations increase neurotransmitter release, and provide an insight into mechanisms underlying the phenotypic differences that are associated with different mutations