Content Reviewers:Yifan Xiao, MD
Aromatic L-Amino Acid Decarboxylase deficiency, or simply AADC deficiency, is a very rare disease in which there’s a decreased activity of an enzyme called aromatic l-amino acid decarboxylase, or AADC for short.
The disease affects babies, which most often seem healthy at birth, but then start developing signs and symptoms during the first months of life.
The severity of the disease can vary between individuals.
AADC deficiency mainly causes movement disorders.
One of the most frequent symptoms is hypotonia of the trunk, which means these individuals have very little muscle tone, making them floppy.
Another frequent symptom is oculogyric crises, which is the abnormal rotation of the eyeballs with elevation of the gaze, as well as uncontrolled movements of the head and neck, agitation, and irritability.
Oculogyric crises can last for hours, and typically occur every 2 to 5 days.
Other less frequent movement disorders include decreased movement called hypokinesia, increased muscle tone of the limbs or hypertonia, and involuntary movements like tremors, twisting movements called dystonia, writhing movements or athetosis, dance-like movements of hands and feet called chorea.
AADC deficiency can also affect the autonomic nervous system, which is the part of the nervous system that controls our internal organs.
Symptoms can include excessive salivation and sweating, droopy eyelids called ptosis, nasal congestion, unstable body temperature, low blood pressure, and low blood sugar or hypoglycemia.
In addition, AADC deficiency can cause gastrointestinal symptoms like reflux, diarrhea, or constipation.
Other less frequent symptoms include seizures, decreased or increased sleep, and decreased or increased reflexes.
Finally, children affected with AADC deficiency often have learning disabilities, developmental delay, and fail to reach milestones like talking or walking.
In addition, they may present feeding difficulties, leading to decreased growth.
Moreover, these individuals are more likely to have medical complications, such as reacting inappropriately to surgery.
As a consequence, many children with severe disease don’t live through childhood.
The cause of AADC deficiency is mutations in the DDC gene, which encodes for the enzyme AADC.
Now, AADC deficiency is an autosomal recessive disease.
This means that, in order to have the disease, an individual must inherit two mutated genes, one from each parent.
Normally, the enzyme AADC is involved in the production of neurotransmitters, which are molecules that our neurons use to communicate.
Now, with AADC deficiency, very few neurotransmitters end up being produced.
As a result, their signals and activities don’t work properly.