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

Three things you didn’t know about epilepsy and genes

Fall colors. Just a brief summary of how this post originated. Eckernförde is a small city north of Kiel and the weekly Sunday destination of my daughter and me because of the wave pool.  This past Sunday, daylight saving and the fact that she didn’t like her dinner had confused the little girl, and we had been awake since 4AM. As a consequence, she fell asleep on the way, and I kept driving to let her sleep. We made it as far as Haddeby, and I used this time to mentally put a post together that I had been planning for some time. These are the three things that are often misunderstood with regards to epilepsy and genes. Continue reading

ST3GAL3 and exome sequencing in autosomal recessive West Syndrome

Autosomal recessive West Syndrome. Exome sequencing and other high-throughput sequencing technologies work best in the identification of recessive disorders. While many cases of West Syndrome are thought to be the result of de novo mutations, recessive inheritance is seen in a subset of patients. In a recent paper in Epilepsia, Edvardson and colleagues now report mutations in ST3GAL3 in a consanguineous Palestinian family with four affected individuals with West Syndrome. This report takes us deep into the chromosomal anatomy of the linkage region, raising the question at what point we can claim that a gene is found. 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