GABRB3 – from febrile seizures to epileptic encephalopathies

Beta-3. Even though the gene for the beta-3 subunit of the GABA-A receptor (GABRB3) has not been mentioned frequently in the context of epilepsy genes, it is a gene that is frequently involved in genetic changed that give rise to epilepsy. Given that GABRB3 is one of the genes found within copy number changes on chromosome 15, it may predispose to human epilepsies through various genetic mechanisms including copy number variations and de novo mutations. In a recent publication in Neurology, we reviewed the phenotypes of patients with GABRB3 variants and found an unusual complexity of sporadic and familial cases. Here are three things that I have learned about GABRB3. Continue reading

GABRB3, 15q dups, and CNVs from exomes

GABAergic. Let’s start out with a provocative statement. There is a single gene that may explain more cases of Lennox-Gastaut Syndrome (LGS) and Infantile Spasms (IS) than you would expect, rivalling SCN1A for the most common gene found in this group of patients. It’s a gene that you are probably aware of but that you may think to be a very rare finding. In a recent publication in Annals of Neurology, the Epi4K consortium published their recent analysis of copy number variations that were derived from exome data. Combining de novo mutations and copy number variations points to GABRB3 as a major player in LGS and IS, explaining probably more than 2% of patients. Let’s find out about the twilight zone, strategies to obtain structural variants from exomes, and the re-emergence of the 15q duplication syndrome. Continue reading

TADA – a joint analysis of de novo and inherited risk factors in autism

Beyond de novo. One of the most robust ways to interpret exome data is the analysis of de novo mutations. However, in addition to the 1-2 de novo events that we can identify in every individual, there is a plethora of inherited variants that often look suspicious. Unfortunately, other than looking at monogenic recessive disorders, we are often incapable of understanding the importance of these inherited variants and tend to ignore them. A recent publication in Nature now overcomes this difficulty by applying a joint analysis of inherited and de novo variants in autism. Continue reading

Beyond the Ion Channel – and back

Where do all the ion channels come from? I would like to start off with a brief commentary about the current state of gene discovery in human epilepsy. Some of our readers rightfully took offense to my previous statement that gene discovery in epilepsy it over – quite the contrary is true, and I apologize for any confusion that I may have caused. Gene discovery in epilepsy is one of the few areas of human genetics with an ongoing, rapid sequence of gene discovery with a tremendous translational potential. But we also need to reconsider the name of this blog – we are far from being beyond the ion channel. The ion channel concept has made a remarkable return in human epilepsy genetics. Let’s find out why. Continue reading

Epileptic encephalopathies: de novo mutations take center stage

The de novo paradigm. De novo mutations play a significant role in many neurodevelopmental disorders including autism, intellectual disability and schizophrenia. In addition, several smaller studies have indicated a role for de novo mutations in severe epilepsies. However, unless known genes for human epilepsies are involved, findings from large-scale genetic studies are difficult to interpret. De novo mutations are also seen in unaffected individuals and only very few genes are observed more than once. Now, a publication in Nature by the Epi4K and EPGP collaborators uses a novel framework to tell pathogenic mutations from genomic noise. Their study provides very strong evidence for a predominant role of de novo mutations in Infantile Spasms and Lennox-Gastaut Syndrome. Continue reading

Hypermutability of autism genes: lessons from genome sequencing

Pushing past the exome. Family exome sequencing has become a standard technology to identify de novo mutations in neurodevelopmental disorders including autism, schizophrenia, intellectual disability and epilepsy. Despite the many advances in the field, exome data is confusing and difficult to interpret. Accordingly, we were wondering what the increase from exome sequencing to genome sequencing might add other than more data and more questions. Now, a recent paper in Cell reports on family-based whole-genome sequencing in autism. And some of the results are quite surprising. Continue reading