Autonomic Dysfunction

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare inherited condition caused by mutations in the DDC gene, which provides instructions for making the AADC enzyme.

This enzyme is needed to make certain neurotransmitters — the chemical messengers that nerve cells use to communicate with each other — including serotonin, dopamine, and the related norepinephrine and epinephrine.

The autonomic nervous system is the branch of the nervous system that controls unconscious bodily functions, such as digestion, breathing, heart rate, blood pressure, and sexual arousal.

Both dopamine and serotonin play critical roles in the normal functioning of the autonomic nervous system. Thus, the lack of these neurotransmitters can cause autonomic dysfunction, which may manifest as a variety of symptoms that can affect many parts of the body.

As with other symptoms of AADC deficiency, autonomic dysfunction most commonly manifests in the first year of life, but there is substantial variation from patient to patient. Treatment of autonomic dysfunction aims at easing the specific symptoms experienced by the patient.

Symptoms of autonomic dysfunction

Eyes

One of the most common manifestations of autonomic dysfunction in AADC deficiency is ptosis, when the upper eyelid droops over the eye. Another common eye-related symptom is miosis, which is when the pupil — the circular black spot at the center of the eye — contracts (gets smaller) excessively.

Nose and throat

Autonomic dysfunction often leads to excessive bodily secretions, which can cause nasal congestion and excessive drooling. Patients also may experience stridor, which is when an obstruction in the larynx (windpipe) results in a harsh vibrating noise when the person breathes.

Sweating and body temperature

Excessive sweating and reduced sweating both can occur as a result of autonomic dysfunction in AADC deficiency. Patients also may experience temperature instability, where the body cannot properly maintain a normal body temperature.

Heart and circulatory system

Autonomic dysfunction can result in low blood pressure, also called hypotension. Many patients experience orthostatic hypotension, which is when blood pressure markedly decreases when a person moves from a seated or lying position to standing up. A severe drop in blood pressure can result in syncope (fainting).

Problems in the autonomic nervous system also can cause problems with the heart, such as bradycardia — an abnormally slow heartbeat, usually defined as less than 60 beats per minute — or abnormal heart rhythms.

Digestive system

In the digestive tract, autonomic dysfunction can result in diarrhea or in severe constipation (sometimes called obstipation). Patients also may experience acid reflux, when acid from the stomach gets up into the esophagus.

Other symptoms

People with autonomic dysfunction may experience low blood sugar, or hypoglycemia. Patients also may have abnormally weak or strong reflexes (hyporeflexia and hyperreflexia, respectively).

Autonomic dysfunction also can contribute to AADC deficiency symptoms such as sleep problems, seizures, and behavior and mood challenges.

 

Last updated: Jan. 11, 2022, by Marisa Wexler MS

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