It has been estimated that genetic factors contribute to at least 40% of all epilepsies (Guerrini et al. 2003b). In the last decade more than 13 genes have been linked to “idiopathic” epilepsies (Lowenstein and Messing 2007) and most genes encode for components of ion channels or for related molecules. Mutations of these known genes only account for a small fraction of patients, thus many other genes causing seizures are yet to be identified. Most of the idiopathic epilepsies do not follow single-gene inheritance and their occurrence in large families is rare. Some rare forms of idiopathic epilepsies have Mendelian inheritance where molecular gene defects have been identified. The discovery of these epilepsy genes has been facilitated by the availability of single large families with many affected members, in which a single mutated gene segregates with most affected individuals. However, even in families with apparently single-gene inheritance there is a degree of complexity. The simple correspondence between genotype and phenotype can break down as the same genotype can result in different phenotypes (phenotypic heterogeneity) or, conversely, identical phenotypes may be due to different genotypes (genetic heterogeneity). The phenotypic variability in such families can be attributed to modifier genes or polymorphisms influencing the phenotypic expression or, alternatively, to environmental factors.
|Title of host publication||The Causes of Epilepsy: Common and Uncommon Causes in Adults and Children|
|Publisher||Cambridge University Press|
|Number of pages||19|
|ISBN (Print)||9780511921001, 9780521114479|
|Publication status||Published - Jan 1 2011|
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