Angelman syndrome is a neurological genetic disorder that affects physical and intellectual abilities.
Around 90% of Angelman syndrome patients experience seizures. They usually appear between ages 18 months and 2 years and may be triggered by high temperatures or fever. Angelman syndrome patients may experience different types of seizures:
- Atonic seizures, characterized by a complete or partial loss of muscle tone;
- Generalized tonic-clonic seizures, characterized by stiff muscles and jerking movements;
- Atypical absence seizures, during which affected individuals are not fully aware of what is happening around them;
- Focal (onset) impaired awareness seizures (formerly known as complex partial seizures), which start in one area of the brain and cause a lack of awareness of one’s surroundings;
- Simple focal motor seizures, which begin in one area of the brain and affect muscle activity;
- Myoclonic seizures, characterized by brief muscle jerks.
How Angelman syndrome causes seizures
Nerve cells in the brain communicate with one another via electrical signals. These cells also send signals to different parts of the body to control movements. Seizures occur when nerve cells transmit sudden uncontrolled bursts of electrical signals, which can trigger other nerve cells to fire additional bursts.
Neuronal function is controlled by the inhibition and excitation of nerve cells by neurotransmitters, or cell-signaling molecules. One such neurotransmitter is GABA. It acts by binding to GABA receptors and inhibits the activity of nerve cells.
It is not exactly understood how Angelman syndrome causes seizures. But researchers think that it is caused by a shift of balance toward too much excitation in nerve cells in the brain.
In Angelman syndrome patients, a part of the maternal chromosome 15 is inactive or deleted. Among other genes, the ubiquitin ligase E3A (UBE3A) gene and genes that provide instructions to build different parts of the GABA receptor reside in this region. Because GABA requires GABA receptors to perform its function, their absence may shift the balance of inhibition and excitation of nerve cells, resulting in seizures.
Seizures in Angelman syndrome patients are challenging to treat and often refractory to therapy. However, in some cases, they may be controlled with anticonvulsants.
Last updated: Sept. 15, 2019
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