Aromatic l-amino acid decarboxylase (AADC) deficiency is a rare neuromuscular condition characterized by an imbalance in the levels of dopamine and serotonin, the neurotransmitters or messenger molecules that help the brain communicate with the rest of the body. Movement disorders are, therefore, common in people with AADC deficiency.
What are movement disorders?
There are two types of body movements — voluntary and involuntary. Voluntary movements are actions that are in an individual’s conscious control, such as throwing a ball or walking. Involuntary movements are those that are beyond a person’s conscious control, such as breathing, eye reflexes, and heartbeat.
The brain regulates muscle contraction and relaxation using neurotransmitters. Erratic communication between the brain and muscles causes movement disorders, or problems with movement. The imbalance in neurotransmitter levels seen in AADC deficiency may result in movement disorders.
Movement disorders include changes — increases and decreases — in the intensity or frequency of voluntary and involuntary movements. They usually are repetitive and painful.
Movement disorders in AADC deficiency
AADC deficiency can cause movement disorders in patients of all ages, from newborns to adults. The severity of the movement disorders varies among patients and usually worsens as the condition progresses. Common movement disorders reported in AADC deficiency are summarized below.
Dyskinesia, bradykinesia, and tremor
Tremor is the shaking movement of one or more body part. It most often affects the hands, but can also occur in the arms, head, vocal cords, torso, and legs.
Dystonia is the abnormal contraction of muscles, causing a movement to be stuck in repetitive action. The muscle spasms can range from mild to severe, and cause repetitive or twisting motions.
Oculogyric crises are dystonia of the eye muscles that control eye movement, causing the involuntary upward movement of the eyeball. In oculogyric crises, the patient’s gaze is stuck in an upward direction. Restricted neck movement, protruding tongue, lip-smacking, anxiety, emotional outbursts such as crying, and extreme exhaustion are some of the accompanying symptoms of oculogyric crises.
Myoclonus is a sudden involuntary muscle jerk. Hiccups are an example of myoclonus that occurs naturally. In AADC deficiency, involuntary muscle jerks can occur at different intensities, last a long time, and interfere with daily activities such as eating, breathing, speaking, or walking.
Treatment of movement disorders
There is no specific treatment for AADC-associated movement disorders. The healthcare team will evaluate the disorder and plan symptom management based on the patient’s needs. The symptoms can last for hours or days. Therefore, making the patient comfortable during an episode, alleviating pain, and managing anxiety associated with the condition are the goals of the treatment.
Movement disorders also are reported in other neurometabolic conditions, including Parkinson’s disease, Wilson’s disease, and tyrosine hydroxylase deficiency. They also are a known side effect of antipsychotic medications.
Last updated: Sept. 20, 2019.
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