Interpretation. There is huge promise in discovering the genetic basis of neurodevelopmental disorders using exome sequencing, but it is often not clear how ambiguous results are communicated to families. In a recent publication in Clinical Genetics, the authors try to understand what happens to exome results as they land on the clinician’s desk – and leave us with the conclusion that diagnostic exome sequencing when reviewed in a clinical setting may have a false positive rate of up to 20% with 5% of false negatives. Continue reading
Issue 2/2015. For the second issue of our publications of the week in 2015, we have selected recent publications on the genetics of Febrile Seizures, the complexities of interpreting variants in large genes and functional studies on progressive myoclonus epilepsies due to mutations in SCARB2 and CTSF. Continue reading
Fever, genes, and seizures. Undoubtedly, febrile seizures are the most common epilepsy syndrome in humans. Up to 5% of children have febrile seizures. In most children, these febrile seizures are self-limiting, and there is no recurrence. Usually, no long-term treatment is required. We know from family studies and twin studies that febrile seizures have a significant genetic component. Now here are two surprising facts: first, the genetic contribution to febrile seizures is entirely unknown. Secondly, to my knowledge, the genetic contribution to the most common epilepsy syndrome in man has not been addressed in any of the current large-scale studies. Let’s review why this is the case and why we should change this. Continue reading
Living in Cologne is a little tough at the moment. Currently, we are in the middle of the Cologne Carnival, the world’s oldest carnival, which started in 1829. Until the upcoming Wednesday the entire city is one big festival. In addition to the 1 million Cologne citizens probably another million tourists will join. Due to this (positive) distraction I will write less than usual. However, I still consider this week’s publications noteworthy. Continue reading
Biggest surprise this week: Imprinted genes interact with non-imprinted genes frequently. But first sequencing reports, statistical frameworks for rare variants analyzes and an impressive translational result.
A novel encephalitis with seizures and the analysis of the effects of antibodies. In their study published in LANCET NEUROLOGY Petit-Pedrol and coworkers characterized serum and CSF samples for antigens in 140 patients with encephalitis, seizures or status epilepticus as well as antibodies to unknown neurophil antigens. High titres of serum and CSF GABAA receptor antibodies are reported to be associated with a severe form of encephalitis with seizures, refractory status epilepticus, or both, which could be exploited for immunotherapy with 15 patients.
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
Modeling disease. Animal models for genetic disease might help in discovering new treatment options, especially when a large number of drugs or compounds can be tested in this model. In a recent paper in Nature Communications, a zebrafish model for Dravet Syndrome is used for medium-throughput screening of compounds approved by the Foods and Drugs Administration (FDA). The authors identify a single compound that is capable of abolishing behavioral and electrographic seizures in SCN1A-deficient zebrafish. Continue reading
G proteins. Intracellular signaling in neurons can occur through various mechanisms including so-called second messengers. G proteins constitute an important part of the signaling cascade that translates the signal from membrane-bound receptors. On neurons, GABA-B receptors or alpha-2 adrenergic receptors use signal transduction through the so-called G alpha-o proteins, which are particularly abundant in the CNS and encoded by the GNAO1 gene. Now a recent paper in the American Journal of Human Genetics describes de novo mutations in Ohtahara Syndrome and movement disorders. Continue reading
You are what you eat. During medical school, I spent a year in Lexington, Kentuck,y as an exchange student. When I went out for lunch with some of my classmates one day, the discussion came up what percentage of my total body protein would be European versus American after one year. It turns out that most proteins have a high turnover rate and are constantly rebuilt and removed. This makes sense as proteins do not have dedicated repair mechanisms as does DNA. However, some proteins seem to linger. A recent study in Cell now identifies long-lived proteins in the brain. And it appears that the gatekeepers of the neuronal nucleus are pretty much built to last forever, and dysfunction of these proteins may contribute to neurological diseases. Continue reading
Compound unknown. GABA is the main inhibitory neurotransmitter in the Central Nervous System and its effect is mediated through GABA receptors. Benzodiazepines are compounds that reinforce the action of GABA in the brain, which gives them antiepileptic properties. Consequently, benzodiazepines are one of the most common groups of antiepileptic drugs used to interrupt acute epileptic seizures. Interestingly, benzodiazepines have their own binding site on the GABA receptor, suggesting that they might actually mimic the effect of another, yet unknown substance that is present in the brain. The identity of this mysterious substance, the endogenous benzodiazepine or endozepine, has been one the romantic mysteries of neuroscience. Now, a recent paper in Neuron provides strong evidence that products of the DBI gene are the long-sought endozepine. Continue reading