The negative exome. Despite writing a lot about the power of next generation sequencing technologies to provide a genetic diagnosis in individuals with severe epilepsies, it is important to remember that most exome tests performed in a diagnostic setting are negative. Even the most optimistic studies do not find a diagnostic yield that exceeds 40%. However, what can be done about the 60-70% of patients who had undergone exome sequencing, the current gold-standard diagnostic testing, but have received a negative test result? A systematic re-analysis after 12-24 months is currently considered one possibility to make sense of existing exome data. In a current publication, the Epilepsy Genetics Initiative (EGI) reports their results of a systematic research-based re-analysis in 166 individuals with epilepsy. In eight individuals, a novel diagnosis could be achieved, including novel genes not known at the time of the initial report and novel mechanisms such as alternative exons. With a diagnostic rate of 6%, this study provides a unique benchmark of what can be expected when exomes initially come back as negative. Continue reading
An unexpected twist in the SCN8A story. SCN8A mutations were first implicated in epilepsy in 2012, when a de novo missense variant was identified in a patient with early infantile epileptic encephalopathy (EIEE) via genome sequencing. Since then, a number of patients with de novo heterozygous SCN8A variants and epilepsy have been reported, firmly establishing the role of SCN8A in EIEE, and we have learned a lot about the associated phenotype, mutation spectrum and disease mechanism within the last four years. Recently, a heterozygous familial SCN8A missense variant was identified in several families with a significantly milder epilepsy phenotype than reported in previous patients. Read further to learn more about the expanded SCN8A-associated epilepsy phenotype. Continue reading
SCN8A. In 2015, SCN8A has emerged as an important gene in epileptic encephalopathy. SCN8A encodes the voltage-gated sodium channel alpha subunit Nav1.6, and was first implicated in epileptic encephalopathy in 2012. Since then, approximately 100 cases of early-infantile epileptic encephalopathy caused by mutations of SCN8A have been identified, and the disorder has been designated EIEE13. Here is what you need to know about SCN8A in 2015.
Issue 10/2015. This week’s publications of the week are about known epilepsy genes that have been around for a while. There are, however, some interesting updates about these genes that are worthwhile discussing. Follow me on a discussion about recent studies on GRIN2A, SCN8A, and DEPDC5. Continue reading