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.