Papers of the week – Copy Number Variations

Dennis' paper of the weekVariations on Copy Numbers. In the third issue of our series on the papers of the week I will focus on the detection and annotation of the most common form of structural variation encountered in genomes. Deletions, duplications and inversions are frequent events, which are surprisingly hard to deal with using sequencing-based tools. Hence, this is an area of active development.

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A metabolic disorder masquerading as adult-onset focal epilepsy

Bella Italia. What a strange day. I am on “emergency duty” for the first day of kindergarten for our daughter. Since the kindergarten is a few meters down the road, I decided to stay home. However, as our windows are currently being replaced, I had nowhere to go. I ended up in a small cafe nearby that I hadn’t noticed before, which turned out to be authentically Italian. Between cornetto e cappuccino, I tried to catch up with some of my blogging duties. For quite some time, I had carried around a case report in the Orphanet Journal of Rare Diseases that I eventually managed to read. In this paper, the authors report on a sib pair with alpha-methylacyl-coA-racemase deficiency (AMACRD). Alpha what?? Exactly. I hadn’t heard of this before, either. However, what raised my interest was the phenotype of one of the patients – adult-onset focal epilepsy. Continue reading

Less is more – gene identification in epileptic encephalopathies through targeted resequencing

Exome no more. Over the last 15 months, we have repeatedly discussed how exome sequencing or genome sequencing is applied to neurodevelopmental disorders in order to discover new candidate genes and to assess the role of known candidate genes. We have also wondered sometimes whether exome sequencing is the most straightforward approach. Now – outpacing the two large international consortia using exome sequencing in epileptic encephalopathies – a recent study in Nature Genetics uses a different approach to uncover the genetic basis in 10% of patients with epileptic encephalopathies.  Targeted resequencing or gene panel analysis is a hybrid technology between candidate gene sequencing and next generation sequencing and focuses only on a subset of candidate genes. While their study provides a comprehensive overview over the genetics of rare epilepsy syndromes, it raises the question whether the era of large-scale exome sequencing is coming to a natural end. Continue reading

CASK aberrations in Ohtahara syndrome

Suppression-burst. Ohtahara Syndrome is a rare epileptic encephalopathy with onset in the first weeks of life. The typical EEG feature of Ohtahara Syndrome is suppression-burst activity, suggesting a profound disruption of cerebral function. Ohtahara Syndrome can be caused by severe brain malformations and neurometabolic disorders. In addition, mutations in ARX and STXBP1 are known causes of Ohtahara Syndrome. In a recent publication in Epilepsia, genetic alterations in CASK were identified in patients with Ohtahara Syndrome and cerebellar hypoplasia. Given that CASK mutations are the known cause for a complex X-chromosomal disorder, this report provides us with an interesting example of what happens when genes underlying distinct clinical dysmorphology syndromes cross over to the epilepsies. Continue reading

Charting a bioethical gray zone: genotype-driven research recruitment

The need for re-contact. Genotype-driven research recruitment refers to the inclusion of research participants in future genetic studies based on the findings from previous studies.  For example, deep sequencing efforts within the EuroEPINOMICS Consortium may generate potentially interesting novel variants that warrant further investigation.  In some cases, it might be necessary to obtain more phenotypic information, in other cases, segregation in the family might be of interest.  Since many variants are rare in the general population, genotype-driven approaches are particularly attractive, i.e. research participants are selected based on genetic findings.  This so-called “bottom up” approach allows for targeted studies without the time-consuming and expensive step of re-screening large patient cohorts.  In the future, genotype-driven research efforts will likely become increasingly common, since it is unlikely that large-scale genomic studies alone will be able to sufficiently characterize rare genetic variants.  However, approaching patients based on genetic research data raises important questions. Continue reading