The calcium connection. Pathogenic variants in genes encoding voltage-gated ion channels have long been known to cause neurological disorders in people. Dravet syndrome, caused by pathogenic variants in the neuronal sodium channel-encoding gene SCN1A, is one of the most common channelopathies. Although sodium and potassium channels play an established role in childhood-onset epilepsies, the role of voltage-gated calcium channels has been less clear. We have known for over a decade that disease-causing variants in CACNA1A cause a spectrum of neurological disorders, including developmental and epileptic encephalopathies. But evidence of a role for other neuronal calcium channels in epilepsy has been sparse until now. Our publication in the American Journal of Human Genetics now explores the phenotype and functional consequences of de novo variants in CACNA1E, representing a new and unexpectedly frequent disease entity.
The X-factor. Interpreting variants in X chromosome genes in a clinical context is an ongoing diagnostic challenge, regardless of whether the variant is identified in a male or female patient. The majority of X-linked conditions affect hemizygous male individuals, with heterozygous carrier girls and women largely unaffected or much less severely affected. PCDH19-Epilepsy is, of course, a notable rule breaker in this regard. However, we are learning that other X-linked conditions don’t play by the traditional rules either, and affected heterozygous females are being described for some other X-linked conditions. In some cases, including SMC1A– and NEXMIF– (formerly called KIAA2022) related disorders, the phenotypes in males versus females are more or less distinct. However, in other X-linked conditions, including IQSEC2-encephalopathy, both affected males and females share a continuum of similar features. A recent publication in Genetics in Medicine explores and expands the spectrum of IQSEC2-encephalopathy and delves into what is similar – and what is distinct – in affected male and female patients. Continue reading
Online. Last week, we held the first online symposium on “Rare Genetic Variants Associated with Neurodevelopmental Disorders”. The meeting covered seven topics which included different genomic approaches used to unravel the genetic architecture of neurodevelopmental disorders and cognitive traits. In total, 117 participants joined the meeting with a peak of 72 participants listening to a presenter. Continue reading
Issue 8/2015. This week’s review of the relevant publications in the field is about a novel risk factor for focal epilepsies, a gene involved in mRNA transport from the cell nucleus, and a small, confirmatory study on exome sequencing in Infantile Spasms.
Variant annotation. In both clinical practice and within existing research projects, we’re often faced with the issue of telling whether a given variant is benign or whether it is pathogenic. In silico prediction tools are designed to help this decision making process. However, there are so many of them and it is often hard to assess which tool works best. In a 2014 publication in Nature Genetics, the CADD score was introduced as comprehensive tool that aims to take the results of many known prediction tools into account. Follow me on a journey that takes us on hyperplanes, support vector machines and every possible variant in the human genome. Continue reading
Protocadherin. There are some genes that we have mentioned less frequently on our blog than we should have. PCDH19 and CDKL5 are two examples of this. With this post, we try to catch up by reviewing some of the new findings related to PCDH19 Female Epilepsy including the role of neurosteroids, anti-NMDA receptor antibodies, stiripentol and the mechanism behind this epilepsy. Continue reading
Issue 7/2015. I am realizing that we are a little behind with our weekly paper review and I hope that we can use the month of July to catch up. Our publications of the week include functional studies on CDKL5 targets that may suggest future therapy development, the recessive/de novo paradox of KIF1A and an attempt to understand the genetics of familial cortical tremor. Continue reading
Dynamin 1. De novo mutations in DNM1 coding for Dynamin 1 are increasingly recognized as a cause for epileptic encephalopathies. However, given the role of Dynamin 1 in endocytosis in a large number of cells, the precise mechanisms how mutations may result in seizures are poorly understood. Now two recent publications in PLOS Genetics and Neurology Genetics explore the functional effects of epilepsy-related DNM1 mutations. The publication of both manuscripts is also a timely reminder to announce our international DNM1 study group that has the aim to better understand the phenotype of this disease. Continue reading
Dual phenotypes. When KCNT1 was first described as a gene for Migrating Partial Seizures of Infancy in 2012, it wasn’t just a novel gene for epileptic encephalopathies. In parallel, the same gene was found to underlie a novel subtype of autosomal dominant nocturnal frontal lobe epilepsies (ADNFLE). At the time, this left us scratching our heads how a gene could cause such distinct, but entirely separate phenotypes. In a recent publication in Epilepsia, Møller and collaborators revisit the phenotypic spectrum of KCNT1. They find that both phenotypes can occur within a single family and that KCNT1 mutations can result in other phenotypes, adding to the mystery of KCNT1. Continue reading
GABAergic. Let’s start out with a provocative statement. There is a single gene that may explain more cases of Lennox-Gastaut Syndrome (LGS) and Infantile Spasms (IS) than you would expect, rivalling SCN1A for the most common gene found in this group of patients. It’s a gene that you are probably aware of but that you may think to be a very rare finding. In a recent publication in Annals of Neurology, the Epi4K consortium published their recent analysis of copy number variations that were derived from exome data. Combining de novo mutations and copy number variations points to GABRB3 as a major player in LGS and IS, explaining probably more than 2% of patients. Let’s find out about the twilight zone, strategies to obtain structural variants from exomes, and the re-emergence of the 15q duplication syndrome. Continue reading