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Because the seizures suffered by the children of this family are similar to those that strike a significant number of children in the general population, there is reason to hope that the identification of this gene could be a key to understanding many more cases of childhood fever-related (or febrile) seizures.
"Febrile seizures are the most common form of childhood seizures. Since they may be associated with the development of seizures and epilepsy later in life, discovery of the responsible gene or genes has important implications for designing new drugs and therapies," said Margaret Jacobs, program director for epilepsy and seizure disorders at the National Institute of Neurological Disorders and Stroke (NINDS), which partially funded the study.
In the United States, about 3 to 4 infants or small children out of 100 will have one or more convulsive episodes during periods of fever. During febrile seizures, nerve cells in the brain fire electrical impulses much faster than usual, often leading to muscular convulsions and loss of consciousness.
For the vast majority of children, the febrile seizures do not cause permanent brain injury and occur only once or a few times. However, about 7% go on to develop other seizure disorders such as epilepsy later in life, a considerably higher risk than in the general population, about 1% of whom suffer from epilepsy.
In this Utah family, the researchers found that 21 of the 48 members participating in the study had experienced one or more febrile seizures during early childhood. Eight of the 21 went on to suffer other seizure disorders.
The University of Utah scientists used a technique called genetic linkage allowing them to determine which segments along chromosomes (the cellular structures that hold genetic information) were shared by all family members who had experienced febrile seizures. They discovered that all those affected shared a portion of chromosome 2. This chromosomal region has not previously been reported to be associated with any seizure disorder.
Techniques other than genetic linkage must now be used to determine what gene in this area underlies the seizures.
"The most obvious task is to identify the gene," said Andy Peiffer, M.D., Ph.D., a researcher at the Eccles Institute of Human Genetics at the University of Utah in Salt Lake City, and one of the authors of the report. "Subsequent studies will focus on determining what percentage of febrile seizures outside this family are caused by mutations in the gene we identify."
For this particular family, the hope is that knowing the location of the gene will lead to identifying the gene and ultimately the protein it produces. Armed with that information, scientists can investigate what role mutations in the gene play in seizures and may even be able to design drugs to compensate for the effects of the mutation in individuals who go on to develop epilepsy disorders.
Thanks to previous research, which has identified some of the genes found along this stretch of chromosome 2, Peiffer and his colleagues already have targeted genes that they suspect might cause the febrile seizures in this family. Some of these genes are ion channel genes, similar to those that the Utah research team has previously found to cause a different, and rarer, seizure disorder. Ion channel genes produce proteins that regulate the electrical activity of brain cells.
But, says Peiffer, "Febrile seizures are very common and are probably caused by mutations in many different, but likely related, genes. The fact that the clinical features of febrile seizures vary somewhat from patient to patient and family to family may be due to the fact that mutations are occurring in different genes or different parts of the same gene."
Other authors of the report were Joel Thompson, M.D., Brith Otterud, Tena Varvil, Chris Pappas, Craig Barnitz, Kristen Gruenthal, Renee Kuhn, and Mark Leppert, all of the University of Utah; and Carole Charlier, who recently accepted a research position in Belgium.
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