Publications of the week – DOCK7, DEPDC5 and the yield of diagnostic gene panels

This week in epilepsy genetics. The following publications are a selection of what was published in the last week. These studies might be relevant for you because they both extend the phenotype of recent gene findings and describe novel genes that you should be aware of. Continue reading

The many faces of PIGA – from paroxysmal nocturnal hemoglobinuria to epileptic encephalopathy

PNH. PIGA codes for a protein involved in the early steps of GPI anchor synthesis, hydrophobic anchors that are attached to a range of proteins, which allows them to be attached to the membrane. This mechanism is important for protein sorting in the endoplasmatic reticulum and the Golgi apparatus. Acquired mutations in PIGA are known to cause paroxysmal nocturnal hemoglobinuria (PNH), an anemia due to destruction of red blood cells. In a recent paper in Neurology, de novo mutations in PIGA are now identified in a complex genetic syndrome, which has early-onset intractable epilepsy as the most prominent feature. 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

PGAP2 mutations and intellectual disability with elevated alkaline phosphatase

Red flags. Despite the availability of a large panel of metabolic and genetic tests as well as high-resolution neuroimaging, the cause of disease in the vast majority of patients remains unknown. This situation also applies for intellectual disability, where there is little to offer in terms of diagnostic procedures once patients are negative for array comparative genomic hybridization (array CGH). In clinical practice, we often hope that some minor clinical or biochemical features may lead us to the correct diagnosis, but in the majority of cases, these investigations lead nowhere. Now, in two back-to-back publications in the American Journal of Human Genetics, two papers describe PGAP2 mutations in patients with non-syndromal intellectual disability with elevated alkaline phosphatase.  Continue reading

Rare Epilepsy Syndromes and the Congenital Disorders of Glycosylation

Rare Epilepsy Syndromes. Motivated by a recent paper in JIMD Reports, I wanted to use this post to present a very rare group of disorders, in which glycosylation of a variety of tissue proteins and/or lipids is deficient. These so-called congenital disorders of glycosylation (CDG) are a highly heterogeneous group of recessive disorders that you might be confronted with. As CDG may masquerade as otherwise non-specific epileptic encephalopathies, you might encounter them clinically or by browsing through exomes of patients with RES. Imtiaz and colleagues now report on two brothers in a large Saudi family with 18 affected siblings. They identified a mutation in DPAGT1, which is known to cause CDG Ij.   Continue reading