The return of the h-current: HCN1 mutations in atypical Dravet Syndrome

Hyperpolarization. More than a quarter of a century ago, physiologists identified an electrical current in neurons and cardiac myocytes that behaved so strangely that it was called the “queer” or “funny” current: it paradoxically caused depolarization upon hyperpolarization. This current was finally named h-current and is mediated by HCN channels. The h-current has been associated with epilepsy through functional studies, but a genetic link has been elusive so far. In a recent publication in Nature Genetics, de novo mutations in HCN1 are identified in patients with early-onset epileptic encephalopathies resembling Dravet Syndrome. Continue reading

Epigenetic signatures – profiling the epilepsies beyond genetics

What is epigenetics? In a single idea: the molecular memory of a cell. The system stores information of previously external (e.g. environmental) or internal (e.g. developmental) stimuli, learns from this experience and responds. A collection of specific tags tells genes whether to be ON or OFF. Hardcore epigeneticists claim that an epigenetic tag should be meiotically and/or mitotically heritable, self-perpetuating, and reversible. DNA methylation is the mechanism coming closest to this ideal. A more liberal definition not focusing on heritability refers to any structural adaptation of the chromatin template that regulates gene expression. This would also include posttranslational histone tail modifications, incorporation of histone variants, chromatin remodeling processes, and action of non-coding RNAs. The large variety, flexibility, interdependence and potential synergistic effects of epigenetic mechanisms could provide the molecular basis for any phenotypic variation in physiological and pathological conditions. In epilepsy research this is especially interesting with regard to the stimulus-driven activity and connectivity of post-mitotic neurons in the adult brain. We set out to study methylation for the most common form of epilepsy in adults. Continue reading

Malaria, seizures and genes

Our old genome. When talking about seizures and genes, “malaria” is usually not the first thing that comes to mind. However, malaria-associated seizures are a major cause of neurological disability in Sub-Saharan Africa. Given the frequency of malaria infections on a worldwide scale, Plasmodium falciparum, the parasite causing malaria, is probably one of the most frequent causes of acute seizures. Our genome has adapted to dealing with parasites over evolutionary time and several disease-causing mutations are thought to be relatively frequent, as they also confer resistance to malaria. For malaria-associated seizures, family studies show an increase in epilepsy in relatives, suggesting that these parasite-induced epileptic seizures may also have a genetic predisposition. A recent study in Epilepsia now investigates malaria candidate polymorphisms as genetic risk factors for malaria-associated seizures. Continue reading

FS and FS+ are two distinct diseases, as suggested by twins

GEFS+ reloaded. The genetics of Febrile Seizures (FS) is one big mystery. Even though large families have been reported and multiple linkage studies have been performed, no single susceptibility gene for Febrile Seizures is known. This is somehow surprising, given that FS is by far the most common epilepsy syndrome. In contrast to common FS, genetic research has been very successful in families with Genetic Epilepsy with Febrile Seizures Plus (GEFS+), where Febrile Seizures Plus (FS+) are the most striking feature in families.  Ever since the definition of the GEFS+ spectrum was established, the distinction from common FS has been a matter of debate. Now a twin study in Epilepsy Research suggests FS and FS+ might actually be two very distinct diseases with little genetic overlap. Continue reading

CACNA1A variants as genetic modifiers in Dravet Syndrome

Genetic modifiers. Dravet Syndrome, formerly Severe Myoclonic Epilepsy of Infancy (SMEI) is a severe epileptic encephalopathy starting in the first year of life. More than 80% of cases of Dravet Syndrome are caused by loss-of-functions mutations in SCN1A, a voltage-gated sodium channel predominantly expressed on GABAergic interneurons. Now, a recent paper in Neurobiological Disorders investigates the role of CACNA1A variants as possible genetic modifiers in Dravet Syndrome. Continue reading