Epigenetic signatures – profiling the epilepsies beyond genetics

What is epigenetics? In a single idea: the molecular memory of a cell. The system stores information of previously external (e.g. environmental) or internal (e.g. developmental) stimuli, learns from this experience and responds. A collection of specific tags tells genes whether to be ON or OFF. Hardcore epigeneticists claim that an epigenetic tag should be meiotically and/or mitotically heritable, self-perpetuating, and reversible. DNA methylation is the mechanism coming closest to this ideal. A more liberal definition not focusing on heritability refers to any structural adaptation of the chromatin template that regulates gene expression. This would also include posttranslational histone tail modifications, incorporation of histone variants, chromatin remodeling processes, and action of non-coding RNAs. The large variety, flexibility, interdependence and potential synergistic effects of epigenetic mechanisms could provide the molecular basis for any phenotypic variation in physiological and pathological conditions. In epilepsy research this is especially interesting with regard to the stimulus-driven activity and connectivity of post-mitotic neurons in the adult brain. We set out to study methylation for the most common form of epilepsy in adults. Continue reading

Guilt by association: SCN1A in Temporal Lobe Epilepsy

GWAS. Genome-wide association studies investigate the association of common genetic variants with disease in large patient samples. While this approach has been very successful in many other diseases, the results in epilepsy research have been less convincing. Given the complexity of epilepsy phenotypes, selection of the right epilepsy phenotype has been an ongoing debate. Now, a recent study in Brain finds an intronic variant of the SCN1A gene that is associated with Temporal Lobe Epilepsy (TLE), the most common epilepsy in man. Interestingly, the association with SCN1A seems to be specific for only a particular subtype of focal epilepsies. Continue reading

Familial Partial Epilepsy with Variable Foci and mutations in DEPDC5

A long story, a complicated phenotype. Massive parallel sequencing technologies were an innovation in neurogenetics and made the discovery of many genes underlying familial epilepsies possible. However, some epilepsy syndromes turned out to be more “stubborn” than others. Now, in a back-to-back submission in Nature Genetics, two groups report on the gene underlying Familial Partial Epilepsy with Variable Foci (FPEVF). And no, it’s not an ion channel this time. Continue reading

The Hippocampus Conspiracy

Slightly misleading. The green and blue histological staining that has become the EuroEPINOMICS logo features a human hippocampus, a part of the human brain that is particularly important in human epilepsy. Temporal Lobe Epilepsy (TLE) is the most common epilepsy in adults and involves the hippocampal region. Ironically, TLE is the human epilepsy that has always been at odds with genetic research. Let’s review what we know about the genetics of TLE and “hippocampal genetics”. Continue reading

A microscopic look at the 16p13.11 microdeletion

The patchwork chromosome. The human genome is a puzzle of duplications, duplications-within-duplications and more complex rearrangements.. Some of these duplications can misalign at meiosis and generate microdeletions and microduplications. The duplication architecture of the human genome is more pronounced in some chromosomes than in others. Chromosomes 15 and 16 are particularly rich in duplications, which is the reason several syndrome-associated microdeletions and microduplications are found there. One of these microdeletions is the 16p13.11 microdeletion. As a recent paper has looked as histological findings in brain tissue of patients with these deletions, it is time to review the only established genetic risk factor that contributes to wide range of epilepsy syndromes. Continue reading

What’s the Frequency, Kenneth? The story of LGI1

Can’t you hear the radio?  “S.W. was spending an afternoon at this girlfriend’s house when he suddenly heard a radio sound in his right ear.  He asked his girlfriend whether she was aware of this sound as well, but he could not understand her answer. S.W. then lost consciousness and convulsed. He presented with a second seizure several months later. S.W. was started on carbamazepine and remained seizure-free. Interestingly, his mother had seizures starting at the same age. Furthermore, his sister had her first seizure at the age of 8 years and frequently reported auras where she would see colourful pictures and hear noises like a familiar song. These episodes sometimes occurred seconds before she had a generalised tonic-clonic seizure.”

LG-what?  This impressive case report taken from Steven Waxman’s Molecular Neurology illustrates a family with lateral temporal lobe epilepsy (LTLE), a rare form of seizure disorder in which auditory features often precede a generalized tonic-clonic seizure. Auditory or acoustic features including radio sounds, machine noises or more complex acoustic phenomena arise from the lateral temporal lobe, a part of the brain important for auditory processing. During a discussion with one of our students last week, I realised that even though we frequently write about microdeletions and novel gene findings on the EuroEPINOMICS blog, some of the classics of epilepsy genetics may sometimes be revisited as well. LTLE is the premier example that genetic epilepsies are not neccesarily due to ion channels. Continue reading