Quantum leap. At the Annual Meeting of the American Epilepsy Society, the Epi4K consortium presented the first data on exome sequencing in epileptic encephalopathies. This data is the most exciting finding in the field of epilepsy genetics in 2012 so far, as it provides a deep insight into the genetic architecture of Infantile Spasms (IS) and Lennox-Gastaut Syndrome (LGS). With the findings presented by the Epi4K collaborators, the epileptic encephalopathies are joining a group of neurodevelopmental disorders with a significant burden of de novo mutations. However, there are important differences that set both IS and LGS apart from diseases like autism, intellectual disability and schizophrenia. Continue reading
Back from AES. I have just come back from the 66th Annual Meeting of the American Epilepsy Society and I would like to share some of the most recent findings that were presented at this meeting. Since we felt that our presentation on the “re-discovery” of SCN1A mutations in SCN1A-negative patients with Dravet Syndrome received quite some attention, I thought that I would share this part of our presentation as a brief screencast. In particular, I would like to thank Anna-Kaisa Anttonen and Anna-Elina Lehesjoki for providing us with the trace files. And of course thanks to everybody in RES who was involved in this.
Now the experiments to find de novo variants for epileptic encephalopathies within the Euroepinomics RES-project are well underway and first data are coming out, it is a good moment to pause and think about what results we can expect, and how these should be interpreted. For this it is very nice that recent large experiments in autism have provided so much useful data. In this post, I will explore what we can expect in experiments in which we perform whole exome sequencing in a group of patients and their parents to identify de novo variants that could be the cause of the disorder.
Are you fully covered? My experience with a phenomenon I shall call exome fallacy began in 2011. While browsing the exomes of a few patients with epileptic encephalopathies, we wanted to have a quick look at whether we could exclude mutations in the epilepsy gene SCN1A in our patients through exome data. As some of you might already guess, the words “exome” and “exclude” don’t go well together and we learned the hard way that each individual exome covers certain parts of the gene quite well. However, if you expect your exome data to have sufficient quality to cover an entire gene in several individuals, you end up disappointed. But there is even more to the exome fallacy than you might think… Continue reading
Monogenic modifiers. Exome sequencing is a well established method to find causative genes in monogenic disorders, with probably more than 100 genes identified through this method in the last two years. In contrast to the ever-expanding list of monogenic diseases solved through massive parallel sequencing, there is widespread skepticism regarding its usefulness in complex genetic disorders. Now, a recent study in Nature Genetics suggests another application for exome sequencing, the identification of modifier genes in monogenic disorders. Continue reading
Alternating Hemiplegia of Childhood (AHC). Acute hemiplegia in children, i.e. weakness of one side of the body, is always a medical emergency. Causes for a sudden hemiplegia can include intracranial bleeds, tumors and rare metabolic disorders. Immediate diagnostic work-up is paramount. In some children, no cause can be found on brain imaging and extensive testing, and the episode remits after hours or days. Strangely, during a following episode, the other side of the body is affected. This condition has been named Alternating Hemiplegia of Childhood (AHC) by Verret and Steele in 1971. AHC is an enigmatic disorder, which is sometimes associated with epilepsy, developmental delay and dystonia. Even though some cases with mutations in SCN1A, CACNA1A, and ATP1A2 have reported, most cases of AHC are unresolved. Given some resemblance with epilepsy and familial hemiplegic migraine, many children with AHC are followed up by epileptologists. The major cause of AHC has now been identified in a recent study… Continue reading
Heritability 2.0. Genome-wide association studies (GWAS) have acquired a slightly negative connotation in the last two years as the results of the enormous efforts were moderate at best. Even though several hundreds of variants have been identified as susceptibility genes for various diseases, the identified genetic risk factors only explain a tiny fraction of the risk for these diseases. Much of what causes common and rare diseases is still unknown – there is a vast discrepancy between population estimates of the genetic contribution and the contribution explained through identified genetic risk factors. This phenomenon has been labeled the “missing heritability”. Now, a recent study using novel statistical tools for GWAS data finds that there is not that much missing after all… Continue reading
In the shade of the furnaces. The EuroEPINOMICS consortium met for the first data analysis meeting at the Luxembourg Center for System Biomedicine (LCSB) from July 5-7th, 2012. What was intended to be a small, private meeting on data analysis eventually turned into a medium-size consortium meeting with lively, sometimes revealing discussions. Belval is a campus in transition, a large steel mill that is currently transformed into the new campus of the University of Luxembourg. The LCSB people are the “first kids on the block”. The atmosphere of Belval is a mixture of industrial romance and pioneer spirit, the ideal backdrop for re-considering our current approaches to deciphering the genetics of the epilepsies. Continue reading
1000 exomes. The EuroEPINOMICS consortium will host its first data analysis meeting at the Luxembourg Centre for System Biomedicine from July 5th to July 7th, 2012, to discuss the results from the high-throughput genomic platforms in the CoGIE, RES, EpiGENet and Epiglia consortia. We will present the first results of the four EuroEPINOMICS programs generated by high-throughput genomic technologies and discuss the overall direction of genetic analysis for the next years, which should soon encompass the proverbial 1000 exomes. In preparation, let’s revisit high-throughput epilepsy genomics. Continue reading
The amazing powers of exome sequencing – a disclaimer. We have recently blogged frequently on the power of exome sequencing in monogenic disorders. Dixon-Salazar now describe in “Exome Sequencing Can Improve Diagnosis and Alter Patient Management” the usefulness of exome sequencing in disease identification in autosomal recessive disorders. Their overall yield is a novel gene discovery in 22/118 probands and a different diagnosis than the initial in 10/118 patients. While title and abstract suggest that exome sequencing is a cure-all improving patient diagnosis and altering patient management, it should be pointed out that this manuscript exclusively deals with autosomal recessive disorders. Only two novel genes out of 20 are described, leaving the reader with little chance to investigate their claim. Many of their families were selected from countries with a high consanguinity including Morocco, where state-of-the-art diagnostic facilities are difficult to access for some patients. The only change in patient management resulting from the altered diagnosis was stopping supplementary Vitamin E in a family with a SPG11 mutation previously thought to have ataxia with vitamin E deficiency. What the altered direction of therapy in a family with a newly identified a-mannosidase type 1 entails, is left for the reader to imagine. The corresponding reference refers to a paper on stem cell transplant as a definitive treatment option, which will probably not be a treatment option for this family from Islamabad, Pakistan. The paper rather shows that exome sequencing is of use in autosomal recessive disorders and might yield surprises. Continue reading