Aromatic L-amino acid decarboxylase (AADC) deficiency is a neurometabolic genetic disease caused by mutations in the DDC gene. This gene contains the information necessary to produce the AADC enzyme, which is required for the production of neurotransmitters, or cell signaling molecules, such as dopamine and serotonin. The lack of the AADC enzyme impairs the coordination between the central nervous system (brain and spinal cord) and the rest of the body.
Among the many symptoms of AADC deficiency, movement disorders such as bradykinesia, dyskinesia (uncontrolled erratic movements), myoclonus (muscle jerk), tremor (shaking movements), oculogyric crises (involuntary upward eye movement), and dystonia (involuntary muscle twisting) affect nearly 50% of all patients.
What is bradykinesia?
Bradykinesia refers to slowness of movement, and is a common symptom in dopamine-deficient diseases such as AADC deficiency and Parkinson’s disease. Bradykinesia is caused by an imbalance in levels of the neurotransmitter dopamine that is required for proper communication between brain and muscle cells.
Bradykinesia is an early sign of AADC deficiency, but is not constantly observed. Periods of normal movement usually alternate with periods of slow movement that affect a patient’s quality of life.
Other indications of bradykinesia include micrographia (small or cramped handwriting), hesitation in movement, and noticeably less blinking. Bradykinesia may also develop into hypokinesia (reduced movement) or akinesia (complete loss of movement).
How is bradykinesia diagnosed?
Bradykinesia is usually first noticed by the family members and friends of the patient. A neurologist or a physician trained in movement disorders can then confirm the presence of bradykinesia. He or she usually asks the patient to perform repetitive movements, such as gripping, tapping their finger and thumb together, and moving their palms up and down.
The neurologist may also look into the patient’s family and medical history to rule out the possibility of medications causing bradykinesia. An MRI scan may be recommended to rule out a stroke or a tumor.
How can bradykinesia be treated?
Physiotherapy and occupational therapy can help considerably in managing bradykinesia. A physiotherapist can recommend an exercise regimen that helps to improve muscle tone and promote free movement. Occupational therapists can recommend the use of aids to help the patient carry out daily activities independently.
Treatments for AADC deficiency that increase the levels of available dopamine in the brain, such as dopamine receptor agonists and monoamine oxidase inhibitors (MAOIs), can also work to alleviate bradykinesia.
Last updated: Oct. 05, 2019
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