Heat at the synapse revisited. STX1B encodes syntaxin 1B, one of three proteins – along with SNAP25 and synaptobrevin – that form the SNARE complex. The SNARE complex is part of the protein machinery responsible for Ca2+-dependent fusion of the presynaptic neuronal cell membrane with the synaptic vesicle to enable neurotransmitter exocytosis. STXBP1 also plays an important role in this process, as the syntaxin binding protein encoded by STXBP1 interacts with the SNARE complex via binding to syntaxin. While pathogenic variants in STXBP1 are a well-established cause of early-onset epilepsies and related neurodevelopmental disorders, after the initial description of STX1B-related epilepsies in 2014, very little more was heard regarding STX1B in the intervening four years. Now, we contributed patients to a publication in Neurology, which provides an update regarding the clinical and genetic landscape of STX1B-related epilepsies. Continue reading
Which test is the right test? In clinical practice, determining an appropriate genetic testing strategy in the evaluation of a patient with unexplained epilepsy is often inconsistent and left to the treating provider, given the lack of evidence-based guidelines. Oftentimes external factors, such as insurance hurdles, dictate the genetic testing that can be ordered. A recent meta-analysis in Neurology attempts to answer the question about which genetic test is most cost-effective in patients with epilepsy, which may aid in the decision making when considering a genetic evaluation of a person with epilepsy. Continue reading
HCN1 update. Hyperpolarization-activated cation channels (HCN) are involved in neuronal pacemaker activity and regulate neuronal excitability through hyperpolarization-activated Ih current. In 2014 de novo missense variants in HCN1 were identified in five unrelated individuals with a Dravet Syndrome-like developmental and epileptic encephalopathy (DEE). However, in the intervening four years relatively little additional evidence has emerged regarding the role of HCN1 in epilepsy. Now, a recent publication in Brain identifies additional individuals with HCN1-related epilepsies and significantly expands the clinical spectrum beyond Dravet-like DEE. Continue reading
NOLA.The American Epilepsy Society (AES) has wrapped up its annual meeting, which was held this year in New Orleans. AES is the largest meeting of epilepsy professionals working in clinical practice, academia, industry, and advocacy. It is a meeting I always look forward to as an opportunity to connect with friends and colleagues from across the world. As we all pack away our beads and digest our beignets, I would like to reflect on some of the major messages I, as an epilepsy genetics clinician and researcher, took away from this year’s AES annual meeting. Continue reading
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
A successful partnership. Making progress in understanding the genetics of the epilepsies requires a successful partnership involving many players. Researchers, clinicians, patients, and families must work together in order to advance scientific goals. Since the first genetic etiology was discovered in a large family with Autosomal Dominant Nocturnal Frontal Lobe Epilepsy nearly 20 years ago, we have made many strides scientifically, in terms of technologies, our clinical classifications, and our knowledge of genetics. Our views on how we approach research from an ethical perspective is also continuing to evolve. Genetic research hinges on the participation of patients and families, and returning results to participants is increasingly viewed as imperative. A recent paper has used the Epilepsy Phenome/Genome Project (EPGP) and Epi4K studies as a case example of the challenges and opportunities regarding returning genetic results to research participants. Continue reading
ClinGen Epilepsy Gene Curation Expert Panel. For the past year I have been a member of the ClinGen Epilepsy Gene Curation Expert Panel, which has been a rewarding professional experience. I have gotten to know several colleagues within the epilepsy and ClinGen communities, I’ve become familiar with resources for gene curation including MONDO and HPO, and I’ve dived deeply into the existing literature linking genes with a broad spectrum of epilepsies. But working with ClinGen has had another unexpected benefit – it has influenced my approach to writing scientific manuscripts. I have been able to apply this knowledge recently when writing a manuscript about a new causative gene for developmental and epileptic encephalopathies. In this post I would like to share five insider tips about what to include in your genetics manuscript so that it can receive full consideration from the ClinGen Epilepsy Expert Panel.
Somatic mosaicism in focal epilepsy. Recent findings highlighted the role of somatic parental mosaicism in epileptic encephalopathies. However, somatic mosaicism has also emerged over the last few years as a prominent mechanism in the pathogenesis of lesional focal epilepsies, including focal cortical dysplasia (FCD) type 2 and hemimegalencephaly. Previous studies have identified the role of mosaicism of genes such as MTOR, TSC1/TSC2, and genes encoding components of the PI3K/AKT pathway in patients with epilepsy secondary to brain malformations. A recent study in Annals of Neurology has identified a new unrelated genetic cause of refractory non-lesional focal epilepsy, which leads us to wonder what role mosaicism may be playing in focal epilepsies without obvious findings on MRI.
Conventional wisdom. Trio whole exome sequencing has been successful over the last five years in identifying underlying genetic etiologies in nearly 50% of patients with epileptic encephalopathies, which is largely owing to the genetic architecture of these conditions. The vast majority of these genetic epilepsies are caused by apparent de novo variants that are present in the patient but not in the mother or father. The conventional wisdom is that the recurrence risk in future pregnancies for parents of an affected child is low to non-existent and traditionally we have quoted a ~1% recurrence risk for future pregnancies. However, a new study published in the New England Journal of Medicine turns this conventional wisdom on its head, identifying detectable somatic mosaicism in approximately 10% of parents tested, which has implications for how we counsel families of children with epileptic encephalopathies – and potentially other genetic conditions due to de novo variants as well. Continue reading