Computational phenotypes. Clinical epilepsy research requires the capturing of complex information in a way that then can be subjected to statistical analysis. For the analysis on the phenotype level, new standards are emerging that are heavily informed by genetic studies. In fact, in addition to the known domain-specific classifications such as the ILAE classification for epilepsy, interdisciplinary action is often required to improve the classification of neurological syndromes for a larger analysis. During the upcoming EMBO Practical phenotyping course in Luxembourg, we will introduce trainees in the field to concepts like the Human Phenotype Ontology (HPO), a controlled vocabulary to characterize syndromes and one of pillars of research in complex syndromes such as epilepsy and how to address aspects not covered in HPO. The course will be held in Luxembourg from Oct 4 to Oct 10, 2018. There has already been a strong interest in this course, but we have a few spots left if you would like to register!
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.
Trio exomes. The concept of neurodevelopmental disorders is an umbrella term including intellectual disability, developmental delay, and autism spectrum disorder. About one quarter of these patients have epilepsy, including epileptic encephalopathy, in which the epileptic activity itself contributes to developmental delay or regression. One major cause of these disorders are de novomutations, which are present in the child but not present in either of the parents. A recent publication in Nature Genetics looked for de novo variants in nearly 6,700 patients with neurodevelopmental disorders, nearly 2,000 of whom had epilepsy. This study is an order of magnitude larger than the largest previous study of this kind and represents an important effort in epilepsy genetics. Here is what we want to review their major findings. Continue reading
Baggersee. With an unprecedented heat wave hitting the northern hemisphere, I eventually found my annual vacation blog post. I wrote blog posts about our beach vacation in Marielyst, Denmark, or Rehoboth Beach, Delaware. However, this year, it took me the better part of two weeks to realize that I had this year’s beach right beneath my feet – the small artificial beach of the Rossenray Lake, a small lake in my home town in Germany where we spent our summer vacation. And here are the three things the beach (and the lake) told me about science in 2018. Continue reading
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
Unravelling the BAFME mystery. The mystery surrounding Benign Adult Familial Myoclonic Epilepsy (BAFME) – also known as Familial Adult Myoclonic Epilepsy (FAME) or Familial Cortical Myoclonic Tremor and Epilepsy (FCMTE) – has persisted for years. BAFME is an autosomal dominant neurological disorder characterized by adult onset of myoclonic/cortical tremor and infrequent seizures. The clinical course is typically considered to be benign. Linkage studies have shown linkage to several regions including 8q24, 2p11.1-q12.2, 3q26.32-q28, and 5p15. A recent publication identified a variant in CTNND2 segregating with disease in a Dutch family with BAFME3, although it remains to be determined how broadly applicable CTNND2 variants are in other individuals with BAFME. Now in an elegant set of experiments by Ishiura and colleagues, a significant proportion of BAFME appears to be solved and is due to expansions of pentanucleotide intronic sequences in SAMD12.
MPP. Mitochondria are indispensable for cellular energy production and require constant protein import, as most mitochondrial genes are encoded in the nucleus. In order for proper targeting, mitochondrial proteins have a specific presequence, which is removed once a protein has found its way into the mitochondria. This function is accomplished by the mitochondrial processing peptidase MPP, which is encoded by the PMPCA and PMPCB genes. In a recent publication in the American Journal of Human Genetics, we identified PMPCB as a novel gene for a complex neurodegenerative condition in childhood and discovered a new disease mechanism for neurological disorders. However, epileptic encephalopathy that initially led to the inclusion of our initial RES study was only one extreme of an unusual disease spectrum. Continue reading
Sodium channel. Voltage-gated channels for sodium ions are a crucial component of helping neurons depolarize and repolarize in a way that enables generation of action potentials. However, in order to function properly, voltage-gated ion channels co-exist in a fragile balance, and genetic alterations leading to functional changes in these channels are known causes of disease. SCN1A, SCN2A, and SCN8A have been implicated as causes for human epilepsy. However, SCN3A encoding the Nav1.3 channel, one of the most obvious candidates, could not be linked to disease so far. In a recent publication, we were able identify disease-causing mutations in this major neuronal ion channel. Interestingly, patients with an early onset and the most severe presentation had a prominent gain-of-function effect that responded to known antiepileptic medications. Continue reading
Ion channels and brain malformations. When the “channelopathy” concept first emerged – the idea that dysfunction of neuronal ion channels leads to neurological disease including epilepsy – it seemed implausible that such dysfunction could lead to malformations of cortical development. However, recent research has suggested that ion channel dysfunction may indeed be linked with brain malformations. In 2017, we saw convincing evidence that germline de novo variants in GRIN2B can cause malformations of cortical development. Some suggestive, but less conclusive, evidence has also linked SCN1A and SCN2A to brain malformations. Now Fry and collaborators demonstrate that de novo pathogenic variants in GRIN1 can also cause significant polymicrogyria, expanding the phenotypic spectrum of GRIN1-related disorders. As a disclaimer, I am also a co-author on the publication by Fry and collaborators. Continue reading
Protocadherins. PCDH19-related epilepsy is the second most common genetic epilepsy, behind Dravet syndrome. PCDH19-related epilepsies display the unusual X-linked inheritance pattern in which heterozygous females are affected but hemizygous males are unaffected. Similarly, somatic mosaic males have also been reported. PCDH19 encodes protocadherin 19, a calcium-dependent cell-cell adhesion molecule that is highly expressed in the central nervous system. The long-hypothesized pathomechanism has been cellular interference, although experimental support has so far been lacking. Now, Pederick and collaborators provide evidence that supports the cellular interference mechanism in PCDH19-related epilepsies, bringing us closer to understanding the biology of this unusual genetic epilepsy. Continue reading