The Cavatica experience – running epilepsy exomes in the cloud

End of the year. The final weeks of the year are always a time when my curiosity for bioinformatics takes over. Four years ago, I was trying to teach myself sufficient command line and bioinformatics to run Denovogear on my computer. Now the field has moved on, from command line language to solutions that aim at bringing data closer to researchers. I hijacked a platform that was initially built for cancer research, CHOP’s Cavatica platform that was developed with Seven Bridges Genomics. In the same way as a few years ago, I started out with a simple question: Can I take an exome completely apart and then re-analyze it to find the SCN1A mutation in DRA1? Continue reading

Here is why CADD has become the preferred variant annotation tool

Variant annotation. In both clinical practice and within existing research projects, we’re often faced with the issue of telling whether a given variant is benign or whether it is pathogenic. In silico prediction tools are designed to help this decision making process. However, there are so many of them and it is often hard to assess which tool works best. In a 2014 publication in Nature Genetics, the CADD score was introduced as comprehensive tool that aims to take the results of many known prediction tools into account. Follow me on a journey that takes us on hyperplanes, support vector machines and every possible variant in the human genome. Continue reading

Robinsoe Crusoe, NFXL1, and speech delay

Founder variant. Specific language impairment (SLI) is a common neurodevelopmental disorder, presenting as delays in acquiring language skills in children who have no hearing loss or other developmental delays. There is a strong genetic component, but the genetic architecture of SLI is entirely unknown. In a recent publication in PLOS Genetics, exome sequencing is performed in the founder population of the Robinson Crusoe Island where SLI is common. Using a combination of exome sequencing and association study, the autors identify a variant In NFXL1 as a plausible candidate for language delay. Continue reading

Cause or coincidence – recessive SCN1A variants in Dravet Syndrome

Recessive epilepsies. Dravet Syndrome is one of the most prominent genetic epilepsies and presents in the first year of life with prolonged fever-associated seizures. Haploinsufficiency of SCN1A, either through mutations or deletions, is the major cause of Dravet Syndrome. In a recent publication in the European Journal of Pediatric Neurology, two families with recessive Dravet Syndrome and biallelic SCN1A variants are reported. Let’s have a look at how to interpret these findings. Continue reading

Flickering lights, endophenotypes, and EEG genetics – CHD2 in photosensitivity

Heritable. Many epilepsy syndromes have signature EEG traits, and these traits are thought to have a strong genetic component. The endophenotype concept suggests that using these epilepsy-related traits in genetic studies will facilitate gene discovery, a concept that has failed us so far in epilepsy research, unfortunately. Now, in a recent publication in Brain, we were able to demonstrate that variants in CHD2 predispose to photosensitivity, an abnormal cortical response to flickering light. Finally, after several decades of persisting difficulties, there is some progress in the field of EEG genetics. Continue reading

SCN8A encephalopathy – and how it differs from Dravet Syndrome

Nav1.6. For some reason, SCN8A always met some resistance. In contrast to other epilepsy genes, it took a while for the community to embrace this gene as a genuine cause of epileptic encephalopathies. A recent publication in Neurology now investigates the phenotypic spectrum of SCN8A encephalopathy – and points out important features that distinguish this condition from Dravet Syndrome. Continue reading

PURA mutations and when diverse phenotypes become a single syndrome

Reverse. With the increasing amount of genetic information available in patients with various neurodevelopmental syndromes, some genes will be observed more than once in patients. In a recent study in the Journal of Medical Genetics, the authors trace back the phenotypes of individuals carrying de novo mutations in PURA. However, there seems to be a wide range of clinical features with a seemingly inverse genotype-phenotype correlation. Continue reading

SETBP1, ZMYND11, and the power of joint exome and CNV analysis

Parallel worlds. There are two fields of genetics for neurodevelopmental disorders that currently produce large amounts of data – the field of copy number variation analysis and the field of exome sequencing. When assigning pathogenicity, information from both genetic technologies are rarely considered jointly. A recent study in Nature Genetics now performs a combined analysis of a large CNV and exome datasets in intellectual disability and autism. Interestingly, this method produces robust results, highlighting novel causative genes. Continue reading

Dynamin 1, the synapse, and why epilepsy gene discovery is now officially over

E2 consortium. Infantile Spasms and Lennox-Gastaut Syndrome are two epilepsy syndromes with a strong genetic component. De novo mutations play an important role in genetic epilepsies. However, given the overall mutational noise in the human genome, telling causative genes from innocent bystanders is difficult. In the largest and most comprehensive analysis so far, our E2 consortium just published a joint analysis of 356 patient-parent trios, which were analyzed by exome sequencing. In addition to implicating DNM1, GABBR2, FASN, and RYR3, this publication sends a clear message: the age of gene discovery in epilepsy is over – from now on, genes will find themselves. Let me tell you what I mean by this. Continue reading

Should we stop talking about heritability in 2014?

Genetic epidemiology. Long before the first epilepsy gene was discovered, clinicians and researchers were wondering about a genetic contribution to epilepsy. Some epilepsy syndrome were found to run in families in an autosomal dominant or recessive pattern. In other epilepsies, there was an obvious excess of affected family members in the immediate or extended family. And this is how we got stuck with the concept of heritability. Let’s review the perils and pitfalls of heritability and ask the question whether we should retire this concept in the current era of genomic medicine. Continue reading