Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare inherited condition in which the communication between the brain and other parts of the body is impaired. Symptoms such as weak muscle tone (hypotonia) and autonomic dysfunction usually appear in early infancy.
Autonomic function refers to bodily and organ functions such as heart and respiratory rate, blood pressure, digestion, and pupillary response.
Causes of autonomic dysfunction
AADC deficiency is caused by a mutation in the dopa decarboxylase (DDC) gene. The DDC gene provides the instructions necessary to build the L-amino acid decarboxylase enzyme. This enzyme performs the last step in the biosynthesis of the neurotransmitters dopamine and serotonin. Neurotransmitters are signaling molecules that enable the communication between nerve cells in the brain and other parts of the body. Peripheral nerves (those outside the brain) control not only muscle movements but also autonomic functions.
Mutations in the DDC gene lead to either reduced production of the L-amino acid decarboxylase enzyme or decreased activity of the enzyme. In both cases, serotonin and dopamine levels are lowered, resulting in both autonomic dysfunction and movement disorders.
Autonomic dysfunction in AADC deficiency may cause the following symptoms:
- Low blood pressure
- Increased or decreased sweating
- Difficulties in controlling body temperature
- Drooping eyelids
- Nasal congestion
- Gastroesophageal reflux disease (backflow of acid from the stomach to the esophagus)
- Constriction of the pupils of the eyes (miosis)
- Fainting (syncope)
- Deregulated heart rate
- Gastrointestinal problems (constipation, diarrhea)
- Cardiac arrest
Treatment of autonomic dysfunction in AADC deficiency is not well established. According to case reports, the vasoconstrictor (agent that constricts the blood vessels) oxymetazoline can help to relieve nasal congestion. Anticholinergic agents, such as trihexyphenidyl, may improve sweating. Fundoplication surgery or GERD surgery can improve gastroesophageal reflux. Gastrointestinal medications can help to relieve digestive problems such as constipation and diarrhea.
Last updated: Sept. 26, 2019
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