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

How a pathogenic de novo mutation in SCN1A ended up in the Exome Variant Server

The omics flood. Large amounts of sequence data are produced every day and we can use the genetic information of several thousand individuals as controls of any present-day genetic study. However, much of research on “traditional” epilepsy genes had been performed prior to the genomic era and often only included limited control cohorts. This begs the question whether a closer look at the currently available data might provide additional information. Now, a recent paper in the Journal of Neurogenetics investigates the presence of reported mutations for epilepsy in large, available datasets. And the results are surprising. Continue reading

A new twist on an old gene: EFHC1 in epileptic encephalopathy

A peculiar gene. There is one gene in the small world of epilepsy genetics that has always troubled me. A gene that has an unknown function and is not expressed in the postnatal brain, but is well established as one of the few genes for autosomal dominant Juvenile Myoclonic Epilepsy (JME). This gene is EFHC1. Now, a recent paper in Epilepsia reports EFHC1 as a possible candidate gene in autosomal recessive epileptic encephalopathy with neonatal onset. The mystery surrounding this gene continues. Continue reading