The second ILAE GWAS or why 30% of genetic generalized epilepsy is explained

Genome-wide association. While most of the neurogenetics community was focused on exome sequencing and the discovery of novel monogenic forms of epilepsy in the last few years, something quite remarkable had happened in the background. Common variants and genome-wide association studies have made a remarkable comeback. The ILAE Consortium for Complex Epilepsy had slowly worked on increasing sample sizes over time, and the second analysis of common variants in common epilepsies was published in late 2018. Sample sizes have almost doubled since the first study in 2014, and as a result, the number of genome-wide significant loci has tripled. However, the most intriguing finding was something that completely caught me by surprise – more than 30% of the heritability of the genetic generalized epilepsies is explained through common variants, approaching the numbers we see in epileptic encephalopathies explained by monogenic causes. This is one more reason to discuss the recent ILAE GWAS in more detail. Continue reading

HCN1 enters the GEFS+ sphere

HCN1 update. Hyperpolarization-activated cation channels (HCN) are involved in neuronal pacemaker activity and regulate neuronal excitability through hyperpolarization-activated Icurrent. 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

AES 2018 Recap: The Epilepsy Community Invades the Big Easy

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

STXBP1-related disorders – one or two disease mechanisms?

Haploinsufficiency. STXBP1-related disorders are one of the most common neurodevelopmental disorders due to pathogenic variants in a single gene. Haploinsufficiency is the proposed disease mechanism and a significant number of individuals have deletions or protein-truncating variants. However, there are also recurrent missense variants in STXBP1, which is often seen in diseases that have a different disease mechanism. In a recent publication in Nature Communications, some of the recurrent variants in STXBP1 are suggested to have an additional disease mechanism, a dominant-negative effect. In this blog post, I want to discuss how we can reconcile both observations and whether STXBP1-related disorders are a single entity with a common disease mechanism. Continue reading

Big data, ontologies, and the phenotypic bottle neck in epilepsy research

Unconnected data. Within the field of biomedicine, large datasets are increasingly emerging. These datasets include the genomic, imaging, and EEG datasets that we are somewhat familiar with, but also many large unstructured datasets, including data from biomonitors, wearables, and the electronic medical records (EMR). It appears that the abundance of these datasets makes the promise of precision medicine tangible – achieving an individualized treatment that is based on data, synthesizing available information across various domains for medical decision-making. In a recent review in the New England Journal of Medicine, Haendel and collaborators discuss the need in the biomedical field to focus on the development of terminologies and ontologies such as the Human Phenotype Ontology (HPO) that help put data into context. This review is a perfect segue to introduce the increasing focus on computational phenotypes within our group in order to overcome the phenotypic bottleneck in epilepsy genetics. Continue reading

CACNA1E encephalopathy: a new calcium channel disease

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.
Continue reading

A critical step towards precision medicine – the ClinGen epilepsy gene curation

Clinical relevance. Pathogenic variants in more than 80 genes have been reported in childhood epilepsies over the last two decades. Developing precision therapies that target the underlying genetic changes is a major research focus and holds the promise to positively influence the lives of thousands of people with individually rare, but collectively common genetic epilepsies. However, in order to develop novel therapies, a formal, unbiased framework is needed to define whether the association between certain gene and disease is in fact valid and that a specific variant is truly pathogenic. This task has proven to be much more difficult than initially expected. Within the larger framework of the ClinGen Consortium, our epilepsy expert panel assesses the clinical validity of genes and variants for human epilepsies, starting with gene curation. In the recently published Human Mutation Special Issue on ClinGen/ClinVar, our panel reports our pilot data and reviews what it takes to connect two increasingly separate fields: the domain of traditional clinical epileptology and the rapidly evolving area of diagnostic genetic testing. Brace yourself: 50% of the alleged gene-disease associations evaluated in our pilot phase did not meet the criteria to be considered clinically valid. Continue reading

A polygenic trickle of common variants in neurodevelopmental disorders

Common variants. In addition to the gradual increase in gene discovery due to exome sequencing, there is a field of human genetics developing in parallel that we have not paid much attention to recently. The role of common genetic variants or Single Nucleotide Polymorphisms (SNP) was initially limited to genome-wide association studies, looking at single variants individually. However, more recently, common variants have been assessed jointly in various diseases, resulting in so-called polygenic scores. In a recent publication in Nature, the polygenic contribution to neurodevelopmental disorders is evaluated. Interestingly, there seems to be a very robust contribution of common variants in neurodevelopmental disorders, even in patients with known de novo variants. Here is a brief discussion on why common variants start getting interesting for the neurogenetics field again. Continue reading

The GABA link in Genetic Generalized Epilepsy

GGE. The Genetic Generalized Epilepsies (GGE) are common epilepsies in children and adults with a prominent genetic contribution. However, genetic risk factors for GGE have been more difficult than most researchers would have expected to pin down. Genome-wide association studies for common variants and association studies for ultra-rare variants have been able to identify several candidate genes, but much of the genetic risk for GGE remain unaccounted for. In a recent study in Lancet Neurology, we have tried a different approach to address the genetic contribution for GGE, looking at gene groups rather than single genes. Using this approach, we were able to detect a signal that would not have been found when looking at individual genes alone, a contribution of rare variants in genes for GABA-A receptors that reliably spans across three different cohorts. Continue reading

The IQSEC2 mystery – exploring the phenotype of an X-linked disease in males and females

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