Aromatic L-amino acid decarboxylase (AADC) deficiency is a neurometabolic condition caused by mutations in the dopa decarboxylase (DDC) gene.
AADC deficiency is characterized by an imbalance in dopamine and serotonin, neurotransmitters or cell-signaling molecules that relay messages from the brain to the rest of the body. The characteristic symptoms of the condition include movement disorders such as dyskinesia.
What is dyskinesia?
Dyskinesia refers to uncontrolled erratic movements that can range from slow, extended muscle spasms to rapid vigorous shaking. The most commonly affected areas are the arms, legs, and torso. However, dyskinesia can also affect other parts of the body.
The type of dyskinesia is based on the type, intensity, and severity of the movement, as well as the area affected. In AADC deficiency patients, three types of dyskinesia are frequently reported:
- Chorea is an irregular, rapid, and repetitive involuntary movement that begins in one part of the body and spreads to other parts. The commonly affects areas are the face, mouth, arms, legs, and torso.
- Athetosis is a slow writhing movement, usually affecting the arms and legs.
- Hyperkinesia is increased muscle activity that causes hyperactivity. It primarily affects the arms, legs, face, and torso.
What causes dyskinesia in AADC deficiency?
The cause of dyskinesia is unclear. However, the fluctuating levels of neurotransmitters such as dopamine and serotonin are thought to contribute to the development of dyskinesia in patients with AADC deficiency. Since the brain regulates muscle activity with the help of neurotransmitters, any change in their levels might interrupt this communication, and result in movement disorders such as dyskinesia.
The AADC enzyme is essential for the production of dopamine and serotonin. In patients with AADC deficiency, a mutation in the DDC gene (which provides the instructions to make the AADC enzyme) results in the enzyme being unable to function properly. As a result, the production of dopamine and serotonin are reduced, and their limited availability may be the cause of dyskinesia.
How is dyskinesia treated?
No medications are currently available to treat dyskinesia in patients with AADC deficiency. Some methods that help manage dyskinesia that’s caused by other conditions include:
- Maintaining good eating habits, developing a meal plan, and regulating protein intake in consultation with a nutritionist.
- Exercising to maintain the proper movement of the muscles in the limbs and torso.
- Resting and adopting stress management techniques, such as meditation and mindfulness.
Managing AADC deficiency with available treatments may also help reduce dyskinesia. However, some medications, such as dopamine receptor agonists, mimic the function of dopamine and, while alleviating some symptoms, they could also overstimulate the muscles, which can result in dyskinesia.
Deep brain stimulation, a surgical technique to alleviate movement disorder symptoms, may also be useful in reducing dyskinesia in certain patients with AADC deficiency.
Dyskinesia is a well-known symptom of other neurometabolic conditions such as Parkinson’s disease.
Last updated: Oct. 03, 2019
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