New clues to the genetic of epilepsy

Two specific areas in chromosome 7 and chromosome 16 have been associated with photosensitivity, an epilepsy-related trait, by a team of European scientists in the January issue of Human Molecular Genetics. Photosensitivity or photoparoxysmal response (PPR) is associated with the most common epilepsy of genetic origin –Idiopathic Generalised Epilepsy (IGE) – and comprehension of the genetics behind it is important to a better understanding of IGE and epilepsy in general.

Epilepsies are a group of brain disorders characterised by recurrent seizures. The disease results from the fact that the neurons (brain cells) of epileptic patients seem to be incapable of properly conduct the nervous signal. This inability leads to excessive and disordered electric activity in the patients’ brain, which can lead to seizures. Seizures trigger involuntary muscle movements and can have a multitude of effects such as altered sensations, changes in awareness, behaviour, movement and/or body function.

Epilepsy affects about 2% of the world population and can create problems in the simplest of everyday activities such as driving, attending a job, school or even staying home alone what has important economic implications for society. Additionally, due to the unpredictability of the seizures that creates a life of constant fear for patients, there is also a extremely high social toll for both patients and their families.

Although treatments, including surgery, are available, for about a third of patients seizures cannot be controlled and new more effective therapies are necessary. In fact, a problem with epilepsy is its multiple causes and consequently the need for different treatments. Disease causes range from abnormal brain development, drug and alcohol abuse, tumours, head trauma or strokes to, in about half of the total cases, defective genes. In this last case, recent advances in the understanding of the human genome have helped to identify genes that can, when altered, lead to disruption of neurons’ normal function and so predispose to epilepsy but much is still unknown.

One example is IGE that accounts for about 40% of all epilepsy cases, being the most common variant of the disease. IGE has a complex genetic origin with several interacting predisposing genes and although investigations on its genetic causes have been done, so far, all studies have proven inconclusive.

Dalila Pinto, Kasteleijn-Nolst Trenité, Bobby P.C. Koeleman and colleagues at University Medical Centre Utrecht and the Epilepsy Institute of the Netherlands in the Netherlands, the Hôpitaux Universitaires de Strasbourg in France and the Institute of Biomedical Sciences Abel Salazar in Portugal decided to approach the study of IGE’s genetic complexity in a different form. The team of researchers choose to study only one of the traits associated and believed to contribute to the disease –photosensitivity – and from this information start constructing the big genetic picture behind IGE.

Photosensitivity or photoparoxysmal response (PPR) is an abnormal visual sensitivity of the brain in response to flickering lights, which, from families and twin studies, is believed to have a genetic origin. PPR appears associated with many idiopathic (of genetic origin) epilepsies, and, at least with IGE, is suspected to be involved in the disease’s mechanism. PPR has the additional advantage of be monitored with an electrocardiogram machine in clinic and so sufferers are objectively identified without the need to rely on clinical symptoms.

Pinto, Trenité, Koeleman and colleagues, using a technique called “genome wide linkage scan” studied sixteen Dutch and French families suffering from a PPR-associated epilepsy, in a total of one hundred and five individuals. The technique consists in the use of several markers, with known localisation in the DNA, to identify/locate the areas in the chromosomes which are conserved among patients and so probably contain the gene or genes associated with disease.

The team of researchers found that chromosome 7 band (or region) 32 and chromosome 16 band 13 were associated with PPR. This result suggests that genes involved in photosensitivity, and consequently with susceptibility to PPR-associated epilepsies, are localised in these areas. Further research is now on the way in order to precisely identify these genes.

Pinto, Trenité, Koeleman and colleagues’ work is very important; by contributing for the identification of susceptibility genes for an epilepsy-related trait their research helps to understand the mechanisms behind epilepsy and ultimately to find better treatment strategies, helping patients to have a better quality of life and maybe one day have the possibility of cure.

Piece researched and written by: Catarina Amorim
(catarina.amorim@linacre.ox.ac.uk)