DNA methylation, somatic mutations, and polymicrogyria

MCDs. Malformation of cortical developments are a frequent cause of intractable epilepsies and, if appropriate, surgical resection may be warranted. Malformations represent a wide range of cortical lesions resulting from derangements of normal intrauterine developmental processes affecting the formation of the cortical mantle. Polymicrogyria (PMG) is one of the most common malformations of cortical development. However, while somatic mutations affecting the mTOR pathway are a known cause of certain subtypes of MCD, the polymicrogyrias have remained elusive. The underlying cause remains unknown in more than 80% of cases and, if identified, may be due to a wide range of underlying genetic causes. In a recent publication, mosaic trisomy 1q was identified as a novel and relatively frequent cause of polymicrogyria, emphasizing the role of somatic mutation detection in malformation of cortical development. 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

Imbalance of a rare second messenger – FIG4 mutations in polymicrogyria

Brain malformations. Various brain malformations are thought to have a genetic basis, and several genes have already been identified. Polymicrogyria is a particular form of congenital brain malformation due to an excessive number of small and sometimes malformed gyri. In a recent publication in Neurology, mutations in FIG4 are described in a familial form of polymicrogyria. However, the FIG4 gene is no stranger in the field of neurogenetics. Continue reading

Microcephaly, WDR62, and how to analyze recessive epilepsy families

Success rate. What is in an exome? There are lots of rare and unknown variants that are hard to make sense of unless we can ask a specific question or have further data to limit the number of genes that we look at. Genetic studies in recessive diseases with limited candidate genes to consider might represent one of the most straightforward cases. In a recent paper in BMC Neurology, the genetic cause of a recessive epilepsy/intellectual disability syndrome in a consanguineous family presenting with primary microcephaly was solved using a single exome of an affected individual. Was this just lucky or can this strategy be applied to any recessive family with a reasonable chance? Continue reading

Copy number variations and the forgotten epilepsy phenotypes

Complexity. Structural genomic variants or copy number variations (CNV) are known genetic risk factors for various epilepsy syndromes. In fact, CNVs might represent the single most studied type of genetic alterations across a very broad range of epilepsy syndromes. There is, however, a group of patients that is usually not investigated in genetic studies: patients with presumable lesional epilepsies or questionable findings on Magnetic Resonance Imaging (MRI). Many of these epilepsies are usually thought to be secondary to the identified lesion, and genetic risk factors are not considered.  In a recent study in the European Journal of Human Genetics last week, we investigated the role of CNVs in a cohort of patients with complex epilepsy phenotypes that were not easily classified into existing categories. Many of patients included had definite or questionable findings on MRI.  The results of our study made us wonder whether the boundary between lesional and genetic epilepsies needs to redrawn. Continue reading

Thalamus, timing and TSC1 deletions

Tuberous Sclerosis. Tuberous Sclerosis Complex (TSC) is a neurodevelopmental disorder caused by lack of function of the TSC1 or TSC2 tumor suppressor gene. With respect to the Central Nervous System, this disease is characterized by so-called tubers, benign tumors consisting of dysplastic neurons that are highly epileptogenic. Accordingly, TSC is one of the most common causes of West Syndrome. However, there is also evidence for neurological dysfunction beyond tubers. Increasing evidence suggests that the mutations alone can result in abnormalities of neuronal networks, resulting in epilepsy, intellectual disability or autism. The thalamus appears to be a key structure that is affected by this dysfunction. Now, a recent study in Cell explores the effects of TSC1 deletions at different developmental stages with respect to neuronal development in the thalamus. Continue reading