What genetic abnormalities are associated with epilepsy?
• Every cell in our body has our genetic information (DNA). We pass this information on to our children.
- The sum of our DNA is called the “genome.” You can think of this as the “library” of all of our genetic material.
- The DNA is packaged in a “chromosome.” Normally we have 23 chromosomes each from our mother and father. You can think of each chromosome as a “book” in the library.
- Each chromosome is made up of hundred of “genes” which you can think of as “words” making up the book. Each gene tells the cell how to do something in particular, for example, make a protein, which is the building block of the cell.
- Each gene is made up of a sequence of DNA base-pairs, which you can think of as the “letters” making up the words in the book.
• Genetic problems can be on the level of the chromosome or in the genes.
- Chromosomal abnormalities:
* Problems may be seen when there is an abnormality with the number of chromosomes or the structure of a chromosome.
- For example, when there is an extra chromosome 21 (trisomy 21), this causes Down Syndrome, which can cause developmental delays and other medical conditions including epilepsy.
- When chromosome 20 has an abnormal ring shape this can cause severe epilepsy.
- Genetic abnormalities:
* When the genes (in our analogy above- words) are “misspelled” with missing or wrong base-pairs, we call the mistake in spelling a “mutation.” Mutated genes may cause the proteins of the cell to not work properly. Mutated genes involved in “brain formation,” “brain metabolism,” and “brain communication” can cause epilepsy.
- Genes involved in BRAIN FORMATION (migration):
* Genes are important in the developing brain because they tell the brain cells where to go. For example, when a certain class of genes is mutated this can result in lissencephaly (smooth brain), because the brain cells haven’t gone to the right spot in the brain when the baby is developing in the uterus. This problem in brain structure will result in faulty brain “wiring” which can cause a seizure focus to develop.
- Genes involved in BRAIN METABOLISM:
* Genes are important for making proteins called “enzymes.” Enzymes break down other proteins in the cell. If the re is a mutation in a gene for an enzyme, then there can be a build-up of a protein in a brain cell, because the usual enzyme to break them down is not present. As the protein levels build up, this can result in damage and death of the brain cell which can result in seizures.
- Genes involved in BRAIN COMMUNICATION (ion channel function):
* Ion channels are proteins that allow the brain cells to communicate with electricity. When there are problems with the ion channels, there may be excessive electrical activity (hyperexcitability) and this might result in epilepsy.