Grey zone. Structural genomic variants or copy number variations (CNV) can be reliably assessed using array comparative genomic hybridization (array CGH) or Single Nucleotide Polymorphism (SNP) arrays. However, for deletions or duplications smaller than 50-100 kB, these technologies have a poor detection rate with many false positive and false negative findings unless platforms are used that target specific candidate regions. Exome analysis, on the other hand, is capable of assessing genetic variation reliably on the single base-pair level. Between both technologies, there is a grey zone of structural genomic variants that are difficult to detect; CNVs smaller than 50 kB are often difficult to assess, and the extent and pathogenic role of these small CNVs is unclear. Now, a recent paper in the American Journal of Human Genetics manages to detect small CNVs through exome data. Their analysis in patients with autism, parents, and unaffected siblings suggests a contribution of small inherited CNVs to the overall autism risk. Continue reading
Category Archives: EuroEPINOMICS
Relationship quality equals bandwidth – a love letter to my wife
Transatlanticism. This is the 165th post on this blog. My wife Katie read every single one of them, correcting my Denglish phrases, adding Oxford commas, and giving me valuable feedback from her unique perspective as a certified genetic counselor with a research background in epilepsy genetics. Today is Katie’s birthday, and I would like to dedicate this post to her by saying thank you and I love you. Katie and I met at the Epilepsy Research Centre in Melbourne, Australia. In 2007, while driving around Lake Alexandrina in South Australia on a road trip, we listened to Transatlanticism by Death Cab for Cutie. This song became emblematic of our relationship for the years to come while we maintained a long-distance relationship between the US (Katie’s Masters in genetic counseling) and Germany (my residency in Kiel). In 2009, after two years of living on different continents, we were finally reunited. If you were to ask me about the main lesson I took away from this time apart, I would sum this up in a single sentence: “Relationship quality equals bandwidth”. This post is a reflection on why quality matters in the communication between geographically separated individuals. It won’t be a purely romantic post. That’s not my style, and that’s ok with Katie – she has corrected this post, as well. Continue reading
Mutation intolerance – why some genes withstand mutations and others don’t
The river of genetic variants. The era of high-throughput sequencing has given us several unexpected insights into the human genome. One of these insights is the observation that mutations or variations can occur in parts of our genome without any major consequences. Every individual is a “knockout” for at least two genes in the human genome. This means that in every individual, both copies of a single gene are disrupted through mutations or small deletions or duplications. In addition, there are dozens, if not hundreds, of genes with disruptive mutations that affect only a single copy of the gene. Similar mutations in specific disease-associated genes, however, will invariably result in an early onset genetic disorder. This comparison already shows that the genes in the human genome differ with respect to the amount of disruptive genetic variation they can tolerate. A recent study in PLOS Genetics now tries to catalogue the genes in the human genome by assessing their mutation intolerance based on the genetic variation seen in large-scale exome datasets. Many genes for neurodevelopmental disorders are highly intolerant to mutations. Furthermore, some genes for monogenic epilepsies show surprising results in this assessment. Continue reading
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
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
Invitation for the EuroEPINOMICS General Assembly in Tübingen
We need to talk. Much has happened in EuroEPINOMICS land ever since the launch of this Eurocores activity in 2011. Back then, exomes were still a realistic, but somewhat remote possibility and the complexity and ambiguity of the human genome was only beginning to be revealed. Now, roughly two years later, we have witnessed major breakthroughs in understanding epilepsy through genetic findings and we have generated large datasets on common and rare epilepsy syndromes that require an unanticipated effort for data mining and sharing. The EuroEPINOMICS Consortium will hold its 2013 General Assembly in Tübingen, Germany, from 30.10-01.11.2013. This meeting will connect all four Collaborative Research Projects and will be the central meeting of this year to jointly discuss our current activities and plans for the future. Continue reading
Three things the beach taught me about science
Endless summer. I am quoting from a representative email that I received this summer from a fellow scientist in the EuroEPINOMICS consortium: “XYZ will reply to you once he is back from his holiday – IF he comes back”. A metereological anomaly had given us one of the longest and most intense summers that I can remember. No rain for roughly four weeks, a new temperature record and a heat that was so intense that the tarmac on the highways started to melt. Accordingly, the motivation in EuroEPINOMICS land to leave the beach behind and return to the office was at an all time low. We spent our summer holiday in Marielyst, Denmark and I just wanted to share some thoughts on how the world of science looks when you’re at the beach. Yes, this post is not too serious. Continue reading
Dravet Syndrome and rare variants in SCN9A
How monogenic is monogenic? Dravet Syndrome is a severe epileptic encephalopathy starting in the first year of life. More than 80% of patients have mutations or deletions in SCN1A, which makes Dravet Syndrome a relatively homogeneous genetic epilepsy. In addition to SCN1A, other genetic risk factors for Dravet Syndrome have been suggested, and current, large-scale studies including EuroEPINOMICS-RES are studying the genetic basis of the minority of Dravet patients negative for SCN1A. A recent paper in Epilepsia now suggests that a significant fraction of patients with Dravet Syndrome also carry rare variants in SCN9A in addition to the mutations in SCN1A. Is a mutation in SCN1A not sufficient to result in Dravet Syndrome, but needs additional genetic modifiers? Continue reading