Genetics of Epilepsy - Basic
Epilepsy is a condition in which a person is susceptible to having mutliple, unprovoked seizures. Seizures are caused by many brain cells firing at the same time. Seizures can take many forms, including a shaking or jerking of the body or simply a brief loss of awareness. About 1 in 100 people have epilepsy. While not all epilepsy is inherited, the following is some general information about the role of genes in causing some forms of epilepsy.
What we call “epilepsy” is actually many different conditions and can have many different causes. For example, brain injury due to head trauma, a brain tumor, or another cause, can lead to epilepsy. When there is no known cause for why someone has epilepsy, it is called “idiopathic” epilepsy and is thought to be due to combination of factors, including a genetic tendency towards seizures.
Genetic factors can contribute to epilepsy in a variety of ways. The most common forms of inheritance in epilepsy are “multifactorial” and “autosomal dominant." Sometimes, other patterns of inheritance, such as “autosomal recessive” inheritance, are seen in epilepsy. For more information on different patterns of inheritance, see the page on How Genes are Inherited.
Multifactorial InheritanceMost idiopathic epilepsy is multifactorial, meaning that it is caused by several genetic and environmental factors acting together. People who are related share many genes, so multifactorial conditions are more common in family members than in the general population.
Evidence for the role of genetic factors comes from the observation that people who have a parent or sibling with epilepsy are more likely to have epilepsy than someone in the general population. In the general population, about 1 in 100 (1%) of people have epilepsy. For someone who has a close relative with epilepsy, the chance of epilepsy is higher. It is about 2-8%, depending on the specific type of epilepsy. On the other hand, there is a 92-98% chance for the close relative of someone with epilepsy to NOT have the same condition.
Autosomal Dominant InheritanceWhile the majority of idiopathic epilepsy is multifactorial, some idiopathic epilepsy is caused by changes in just one gene (called a single gene disorder). In a minority of families, there may be several people who have a similar type of epilepsy. In these cases, the epilepsy may be inherited in an autosomal dominant pattern.
Our bodies are made up of billions of cells. Inside each of our cells are genes, which are sets of instructions for how we grow and develop. We have two copies of every gene, one from the mother and one from the father. Sometimes, one of the copies of a gene may have a change in it which stops it from working properly. In the case of autosomal dominant conditions, having one non-working copy of a gene causes the disease. In other words, the non-working copy of the gene is dominant over the normal, working copy of the gene.
Some of the genes which are changed in epilepsy are genes which control how brain cells send signals to each other. These gene changes do not generally have an effect on intelligence. They simply make the brain cells more likely to fire together and cause a seizure.
People who have an autosomal dominant form of epilepsy have one working copy and one non-working copy of a gene in every cell of their body. Each time a person with autosomal dominant epilepsy has a child, there is a 50% (one half) chance of passing on the working copy and a 50% (one half) chance of passing on the copy which does not work. A child who inherits the non-working copy of the gene will also have epilepsy. A child who inherits the working copy of the gene will not have that type of epilepsy and cannot pass that type of epilepsy on to his or her children.
Note: Human genetics is an extremely complex topic. This website is meant only as an introduction and overview. If you are concerned about how genetics may affect your health, please consult a health care professional.URL: http://www.oocities.com/geneinfo
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Latest revision: © December, 2001 by Julie S. Mak