CACNA1A: the unusual tale of two proteins encoded by a single gene

CACNA1A. CACNA1A is a large gene with a long history. Its first gene-disease association was with spinocerebellar ataxia type 6 (SCA6), an adult-onset progressive neurological disorder. Next, it was found to be associated with episodic ataxia and familial hemiplegic migraine. It took several more years before it was also found to be associated with epilepsy, developmental delay, and a more severe form of hemiplegic migraine. Here is a blog post on the range of neurological disorders associated with CACNA1A and the mechanism driving it.

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CACNA1A – five things to know in 2022

Epilepsy genes. It has admittedly been quiet around the gene pages on our blog and many pages require an update. When we initially launched the Epilepsiome pages, we wanted to create a small resource for gene-based information according to the “what you need to know” principle, a condensed digest regarding epilepsy genes written by clinicians and researchers with deep expertise in the field. We chose CACNA1A as the first gene to get an update. The reason for this is the following: Laina has taken on the role of modernizing this blog and CACNA1A is the main condition that she is working on. Here are five things to know in 2022 about CACNA1A. Continue reading

CACNA1A, hemiplegia, and the genetic of migraine

FHM. Each time I mention CACNA1A and its association with migraine to clinicians and scientists outside the field of pediatric neurology or neurointensive care, I need to take one step back. Yes, CACNA1A is one of the monogenic causes of hemiplegic migraine, but the clinical condition that we are typically concerned with has relatively little to do with common migraines. In contrast, we are talking about a neurodevelopmental disorder often associated with developmental concerns, ataxia, epilepsy and episodes of hemiplegia that may results in brain swelling and can be life-threatening. This condition, typically referred to as familial hemiplegic migraine type 1 (FHM1), neither runs in families nor does it typically result in migraine features. The historical naming conventions complicate awareness of one of the most enigmatic events in neurology, which we refer to as hemiplegic migraine episodes for a lack of a better word. However, I wanted to approach CACNA1A from a different perspective, given the recent publication of a large migraine genetic study in Nature Genetics. Continue reading

CACNA1A – this is what you need to know in 2015

P/Q. This week’s gene of the week is an atypical epilepsy gene, which is the main reason that this post is only coming out on Friday rather than Monday. Even though I was initially highly motivated to put something together on CACNA1A, I soon discovered that this gene is overwhelming. CACNA1A is a gene for both a channelopathy and trinucleotide repeat disorder, a gene for early childhood-onset and late onset adult neurological disorders, and a gene responsible for both episodic neurological conditions and neurodegenerative diseases. I have tried to put this into a coherent format. Here is what you need to know about CACNA1A in 2015. Continue reading

SCN1A and Dravet Syndrome – your questions for the Channelopathist

Comments. After posting our 2015 update on what you should know about SCN1A, we received a number of comments on our blog and by email. We usually have the policy to respond to every comment individually. However, after we had realized that we had fallen behind with a few replies for several weeks, we felt that it might be worthwhile rephrasing some of the questions as general topics to write about, especially since many of your questions raised interesting points. Here are the questions that you asked regarding SCN1A and Dravet Syndrome. Continue reading

Beyond recessive – KCNC1 mutations in progressive myoclonus epilepsy

PME. The progressive myoclonus epilepsies (PME) are a particular subtype of seizure disorders characterized by progressive myoclonus, generalized seizures and cognitive deterioration. Known causes of PME include recessive mutations in several well-known genes, but the genetic cause is unknown in a significant proportion of patients. Now, in a recent paper in Nature Genetics, de novo mutations in KCNC1 are identified as a novel cause of progressive myoclonus epilepsies. In addition to elucidating the genetic basis in a significant subset of patients with PME, the authors demonstrate that de novo mutations play an important role in a group of diseases usually thought to be recessive. Continue reading

CACNA2D2, the ducky mouse, and what it takes to be an epilepsy gene

Subunit. Spontaneous mouse mutants help to identify candidate genes for disease mechanisms and have hinted at an important role for ion channels in epilepsy long before the first human channelopathies were identified. The ducky mouse has absence seizures and suffers from ataxia. A truncation mutation in CACNA2D2 could be identified in this phenotype, encoding for an auxiliary calcium channel subunit. This finding emphasizes the role of calcium channels in absence seizures and begs the question whether genetic variation in CACNA2D2 is also involved in human epilepsy. A recent publication in PLOS One now identifies the second recessive CACNA2D2 mutation in a patient with epileptic encephalopathy. But are two independent cases sufficient anymore to claim causality? Continue reading

Modifier genes in Dravet Syndrome: where to look and how to find them

Converging thoughts. During late 2013, I had several unrelated discussions about the possible role of genetic modifiers of SCN1A in Dravet Syndrome. To some extent, SCN1A is a paradox. One the one hand, the connection between Dravet Syndrome and SCN1A is one of the clearest connections between gene and disease that we see in genetic epilepsies. On the other hand, we see a remarkable phenotypic heterogeneity in families, and some presumably pathogenic SCN1A variants can also be identified in unaffected control individuals. This leaves us with the question whether there are genetic modifiers in Dravet Syndrome that might help provide some insight into additional mechanisms of disease. This post is a collection of 10 individual thoughts that emerged during the discussions last year. Continue reading