Triad. There are three microdeletions in particular that increase the risk for the Idiopathic/Genetic Generalized Epilepsies (IGE/GGE). This triad includes microdeletions at 15q13.3, 16p13.11 and 15q11.2, which are hotspot deletions arising from the particular architecture of the human genome. While the association of these microdeletions with epilepsy and other neurodevelopmental disorders including autism, intellectual disability and schizophrenia is well established, the core phenotype of these variants remains elusive, including the question whether such a core phenotype actually exists. In a recent paper in Neurology, Mullen and collaborators zoom in on a possible core phenotype of these microdeletions. The authors investigate a phenotype in which these microdeletions are particularly enriched: generalized epilepsy with intellectual disability. Continue reading
Monthly Archives: September 2013
Are there incidental findings in exomes that require immediate action?
Guidelines. High throughput sequencing generates an unprecedented amount of genetic data. Most exomes are generated in a specific context, i.e. the genetic data is screened for variations in specific candidate genes or screened for de novo mutations. However, these approaches only use a small fraction of the genetic data generated per individual. High-throughput sequencing may also reveal clues towards possibly relevant diseases, and there is an ongoing debate if and how incidental findings should be returned to individuals undergoing high-throughput sequencing. Now, a recent paper in the American Journal of Human Genetics uses a very stringent clinical approach to assess the frequency of medically actionable findings in exome data. The results are not what you would think, and there is an urgent need to fix the existing databases. Continue reading
Temperature rising: 17q12 microduplications and GEFS+
GEFS+, meet CNV. Microduplications at 17q12 have been identified in various neurodevelopmental disorders and in some unaffected individuals, a pattern familiar from other structural genomic variants such as microdeletions at 16p13.11 and 15q11.2. In contrast to the corresponding microdeletion, most 17q12 microduplications are inherited. This suggests that the microduplication is a risk factor, but does not fully explain the phenotype. In a recent paper in Neurology, Hardies and collaborators look at the families of 17q12 microduplication carriers with epilepsy. And this is when they noticed something strange. Continue reading
The genetics of treatment response in newly diagnosed epilepsy
Two questions. There are two main questions that we would like to answer with genetics in the field of epilepsy. First, are there genetic risk factors for epilepsies and if so, what are they? Secondly, are there genetic factors that help us understand how patients react to treatment, i.e. are there genes that predispose to response to antiepileptic drugs or that might be associated with side effects? While we have made much progress in answering the first question by identifying many epilepsy genes, there have been few answers for the second question, the field of pharmacogenomics. Now, a recent study in Human Molecular Genetics looks at potential genetic risk factors for the response to antiepileptic drugs in newly treated epilepsy. This is a study that needed to be performed and that we were waiting for. Continue reading
Why I am still struggling with SCN9A in Dravet Syndrome
Susceptibility. Two weeks ago, we published a post on rare variants in SCN9A as potential susceptibility genes for Dravet Syndrome with mutations in SCN1A. Ever since reading the article by Mulley and collaborators, I had tried to come up with an idea of what the genetic architecture might look like if both de novo variants and inherited variants contribute. I wanted to follow up on my earlier post with this brief back-of-the-envelope calculation. Continue reading
Guilt by association: SCN1A in Temporal Lobe Epilepsy
GWAS. Genome-wide association studies investigate the association of common genetic variants with disease in large patient samples. While this approach has been very successful in many other diseases, the results in epilepsy research have been less convincing. Given the complexity of epilepsy phenotypes, selection of the right epilepsy phenotype has been an ongoing debate. Now, a recent study in Brain finds an intronic variant of the SCN1A gene that is associated with Temporal Lobe Epilepsy (TLE), the most common epilepsy in man. Interestingly, the association with SCN1A seems to be specific for only a particular subtype of focal epilepsies. Continue reading
Dravet Syndrome, zebrafish and clemizole
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, GNAO1 mutations and Ohtahara Syndrome
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
Thalamus, timing and TSC1 deletions
Tuberous Sclerosis. Tuberous Sclerosis Complex (TSC) is a neurodevelopmental disorder caused by lack of function of the TSC1 or TSC2 tumor suppressor gene. With respect to the Central Nervous System, this disease is characterized by so-called tubers, benign tumors consisting of dysplastic neurons that are highly epileptogenic. Accordingly, TSC is one of the most common causes of West Syndrome. However, there is also evidence for neurological dysfunction beyond tubers. Increasing evidence suggests that the mutations alone can result in abnormalities of neuronal networks, resulting in epilepsy, intellectual disability or autism. The thalamus appears to be a key structure that is affected by this dysfunction. Now, a recent study in Cell explores the effects of TSC1 deletions at different developmental stages with respect to neuronal development in the thalamus. Continue reading
Methusalem proteins in the brain
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
