The return of the h-current: HCN1 mutations in atypical Dravet Syndrome

Hyperpolarization. More than a quarter of a century ago, physiologists identified an electrical current in neurons and cardiac myocytes that behaved so strangely that it was called the “queer” or “funny” current: it paradoxically caused depolarization upon hyperpolarization. This current was finally named h-current and is mediated by HCN channels. The h-current has been associated with epilepsy through functional studies, but a genetic link has been elusive so far. In a recent publication in Nature Genetics, de novo mutations in HCN1 are identified in patients with early-onset epileptic encephalopathies resembling Dravet Syndrome. Continue reading

GPHN deletions in IGE and mutation-dependent recessive inheritance

Bild1Living in Cologne is a little tough at the moment. Currently, we are in the middle of the Cologne Carnival, the world’s oldest carnival, which started in 1829. Until the upcoming Wednesday the entire city is one big festival. In addition to the 1 million Cologne citizens probably another million tourists will join. Due to this (positive) distraction I will write less than usual. However, I still consider this week’s publications noteworthy. Continue reading

Treatable causes of intellectual disability and epilepsy that you don’t want to miss

Think metabolic. We have discussed de novo mutations as a cause of epileptic encephalopathies repeatedly on our blog. While there is emerging evidence that de novo mutations in established genes such as SCN1A or CDKL5 or novel genes including GNAO1 or CHD2 are a major cause of genetic morbidity in patients with epileptic encephalopathies, investigations for de novo mutations are not the immediate knee-jerk reaction in clinical practice. In fact, if a child presents with an epileptic encephalopathy, excluding inborn errors of metabolism (IEM) takes priority. While metabolic causes of epileptic encephalopathies are rare, they need to be excluded as some of these conditions are treatable. In a recent review in Molecular Genetics and Metabolism, van Karnebeek and colleagues review the 89 causes of intellectual disability that are potentially treatable. Many of these conditions also present with epilepsy. They present an updated diagnostic algorithm and provide an online resource for these conditions – in a nutshell, there is an app for that.  Continue reading

Papers of the week – Encephalitis-antibodies, FAN1, Art and Parent-of-Origin Effects

Dennis' paper of the week

Biggest surprise this week: Imprinted genes interact with non-imprinted genes frequently. But first sequencing reports, statistical frameworks for rare variants analyzes and an impressive translational result.

A novel encephalitis with seizures and the analysis of the effects of antibodies. In their study published in LANCET NEUROLOGY Petit-Pedrol and coworkers characterized serum and CSF samples for antigens in 140 patients with encephalitis, seizures or status epilepticus as well as antibodies to unknown neurophil antigens. High titres of serum and CSF GABAA receptor antibodies are reported to be associated with a severe form of encephalitis with seizures, refractory status epilepticus, or both, which could be exploited for immunotherapy with 15 patients.

Continue reading

Papers of the week – WES Meta analysis, Dravet mice & large sequencing studies

Bild1Time flies – already thursday night again.  Here are updates on study designs to identify rare pathogenic mutations in neurodevelopment diseases, an epilepsy animal model study as well as novel statistical frameworks for large genetic screens.

The placebo effect. In a recent paper in Science Translational Medicine the group of Kam-Hansen investigated the effect of altered placebo and drug labeling changes and its outcome in patients with episodic migraine. Their results suggest that the placebo accounted for more than 50% of the drug effect.

Continue reading

Papers of the week – Comorbidity clusters, Epigenomic annotation & exome-based TDT

Finally, I have finished my PhD. Bild1After focussing on writing and defending my thesis for the last few months, I am now ready to focus on research again. Because I am understandably in a very happy mood, this week’s selection of papers also reflects the fun aspects of science beside neurogenetics and genomics. Continue reading

Story of a genetic shape-shifter: SCN2A in benign seizures, autism and epileptic encephalopathy

The other sodium channel gene. The week before Christmas, the Kiel group identified its first patient with SCN2A encephalopathy. At the same time, a questionably benign SNP in the same gene is haunting our Israel Epilepsy Family Project. Time to review the mysterious SCN2A gene that initially entered the scene as a candidate for a rare, benign familial epilepsy syndrome – only to return as one of the most prominent genes for autism, intellectual disability, and epileptic encephalopathies to date. Continue reading

Beneath the surface – the role of small inherited CNVs in autism

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

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

Identifying core phenotypes – epilepsy, ID and recurrent microdeletions

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