ARX – a 2017 Update

Aristaless. When you look at the genes for neurodevelopmental disorders identified in modern-day exome studies, one gene is notably absent: ARX. The X-chromosomal aristaless related homeobox gene was one of the first genes for epilepsies and brain malformations to be discovered. Pathogenic variants in ARX can be identified in male patients with a variety of neurodevelopmental disorders including idiopathic West Syndrome – accordingly, ARX is on the differential list for patients with intractable infantile spasms without a known cause. One of the reasons why we hear so little about ARX is the fact that this gene is poorly covered in exomes. Furthermore, one of the major disease-causing variants is a repeat expansion that cannot be assessed through exome studies at all. Here is a brief summary of what we know about ARX in 2017. Continue reading

MECP2 – Rett Syndrome in the era of exome-first studies

Rett. We have written very little about MECP2 on Beyond the Ion Channel. MECP2 is the gene for Rett Syndrome, a neurodegenerative disorder almost exclusively affecting females. Classical Rett Syndrome is characterized by developmental regression in the first two years of life and the development of distinctive hand movements, which historically led to Rett Syndrome being considered a recognizable entity. This blog post is the introduction to our MECP2 Epilepsiome page. However, in 2016, a time when many genes are re-defined by exome studies, I was wondering whether Rett Syndrome is still the classical syndrome that I initially learned about.

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SCN1A – what’s new in 2016?

The story of SCN1A. Variants in SCN1A were first reported in association with epilepsy in 2000, when familial heterozygous SCN1A missense variants were identified in two large families with GEFS+. The phenotype was characterized by incomplete penetrance and significant variable expressivity between family members, making it clear from the beginning that the SCN1A story would not be simple. Within the next few years, we learned that SCN1A variants could cause a wide spectrum of epilepsy phenotypes, including GEFS+, Dravet syndrome, intractable childhood epilepsy with generalized tonic-clonic seizures, and, less frequently, infantile spasms and simple febrile seizures. As it became clear that SCN1A variants played an important role in genetic epilepsies, focus turned towards understanding the mechanism underlying seizure genesis, as well as identifying management and therapy options. Even after 15 years of study, our understanding of SCN1A-related epilepsy is still evolving. Keep reading to learn more about the most recent discoveries related to SCN1A. Continue reading

TBC1D24 – what’s new in 2016?

The story of TBC1D24. As with many epilepsy genes, the TBC1D24 story increases in complexity over time. Initially described to be associated with autosomal recessive familial infantile myoclonic epilepsy by Falace and colleagues and with autosomal recessive focal epilepsy by Corbett and colleagues in 2010, pathogenic variants in TBC1D24 have since been identified as a major cause of DOORS syndrome and have also been identified in individuals with familial malignant migrating partial seizures of infancy, progressive myoclonus epilepsy, early-onset epileptic encephalopathy, and autosomal dominant and autosomal recessive non-syndromic hearing loss. However, little is known about a potential genotype-phenotype correlation of TBC1D24-related disorders, as well as the underlying mechanism. Keep reading to learn more about recent discoveries related to TBC1D24. Continue reading

Closing the knowledge gap – this is SYNGAP1

Mind the Gap. Ever since its discovery in 2009, SYNGAP1 has been a prominent gene connected to autism and intellectual disability. However, even though probably more than half of all patients with pathogenic SYNGAP1 variants have seizures, it was never a gene that was particularly prominent in the epilepsy field. In a recent publication, we were able to delineate the epilepsy phenotype of patients with pathogenic SYNGAP1 variants, identifying a peculiar combination of generalized seizures types. Here is a blog post about a gene that I admittedly knew very little about before we started working on it. Continue reading

PCDH19 – what’s new in 2016?

The story of PCDH19. The clinical features and unique inheritance pattern of PCDH19-related epilepsy were first described in 1971, and the clinical entity was coined Epilepsy in Females with Mental Retardation (EFMR), due to the presence of epilepsy and cognitive disability that seemed to be limited to females. Pathogenic PCDH19 variants were identified in females in 2008, and it soon became clear that PCDH19 is a major player in the genetic basis of epilepsy, with more than 100 patients with PCDH19 variants described to date. The inheritance pattern is one of the most striking features of this condition. Heterozygous females are affected, while hemizygous transmitting males are spared. At the cellular level, the disease mechanism seems to be loss of function. However, at the tissue level, the current hypothesis for the underlying mechanism is gain of function, resulting from the co-existence of two different PCDH19-expressing neuronal populations in females and mosaic males. Keep reading to learn more about recent discoveries related to PCDH19. Continue reading

What’s new with SCN8A – a 2016 update

An unexpected twist in the SCN8A story. SCN8A mutations were first implicated in epilepsy in 2012, when a de novo missense variant was identified in a patient with early infantile epileptic encephalopathy (EIEE) via genome sequencing. Since then, a number of patients with de novo heterozygous SCN8A variants and epilepsy have been reported, firmly establishing the role of SCN8A in EIEE, and we have learned a lot about the associated phenotype, mutation spectrum and disease mechanism within the last four years. Recently, a heterozygous familial SCN8A missense variant was identified in several families with a significantly milder epilepsy phenotype than reported in previous patients. Read further to learn more about the expanded SCN8A-associated epilepsy phenotype. Continue reading

DEPDC5 – this is what you need to know in 2015

DEPDC5. We have selected DEPDC5 to be our gene of the week. DEPDC5 is currently the most common known gene for focal epilepsies. DEPDC5 mutations cause familial focal epilepsy with variable foci, an epilepsy syndrome with autosomal dominant inheritance where the affected family members can have different types of focal epilepsies, most frequently frontal lobe epilepsy. Despite seizure semiology that varies among family members, it is constant for each individual. Continue reading

WDR45 – this is what you need to know in 2015

BPAN. We have selected WDR45 to be our Epilepsiome gene of the week. WDR45 was initially identified as the causative gene for a rare phenotype referred to as static encephalopathy with neurodegeneration in adulthood (SENDA), which belongs to a group of neurodegenerative disorders that have accumulation of iron in the CNS as the common feature. In contrast to the narrow and very specific phenotype in most other disorders in this group, the phenotypic spectrum of WDR45 has expanded significantly since the initial discovery in 2013. Mutation in WDR45 can be identified in patients with a broad range of neurodevelopmental phenotypes including epileptic encephalopathies. Continue reading