Childhood absence epilepsy
Childhood absence epilepsy is a condition characterized by frequent, brief staring spells known as absence seizures that typically begin between the ages of 3 and 8.
Overview
Affected children experience absence seizures (petit mal seizures), which are brief episodes of impaired consciousness. During these episodes, the child is unaware of their surroundings and does not respond to others. These seizures last only a few seconds but can occur up to 200 times per day.
Symptoms and Progression
- Staring Spells: The hallmark of absence seizures.
- Febrile Seizures: Some children experience convulsions brought on by high fever before developing absence epilepsy.
- Adolescence: In most cases, seizures disappear during the teenage years. However, some individuals may continue to have absence seizures into adulthood or develop other types of seizures, such as generalized tonic-clonic or myoclonic seizures.
Causes
The genetics of this condition are complex, likely involving multiple genetic changes or a combination of genetic and environmental factors.
- GABAA Receptor Mutations: Several genes provide instructions for subunits of the GABAA receptor, which acts as an ion channel. These receptors normally block (inhibit) signaling between neurons. Mutations reduce the number of functional receptors, leading to overstimulation of neurons and triggering seizures.
- Calcium Channel Mutations: These channels transport calcium ions into cells and help control the release of neurotransmitters. Overactive calcium channels can cause neurons to become overstimulated, leading to seizure activity.
Inheritance
Childhood absence epilepsy does not have a straightforward inheritance pattern. When associated with GABAA receptor or calcium channel gene mutations, it appears to follow an autosomal dominant pattern. However, it exhibits reduced penetrance, meaning some individuals who carry the altered gene never develop the condition.