Aromatic L-amino acid decarboxylase (AADC) deficiency is caused by mutations in the DDC gene that lower the activity of the AADC enzyme. This enzyme plays an important role in producing neurotransmitters, or cell signaling molecules, in the brain such as dopamine and serotonin. Their deficiency leads to problems in the transmission of signals between nerve cells, and poor communication between the brain and the rest of the body.
Early signs and symptoms
The symptoms of AADC deficiency manifest within the first year of life, and lead to severe delays in children reaching developmental milestones like walking and talking. Other common symptoms include hypotonia or weak muscle tone, muscle stiffness, and athetosis (involuntary writhing movements of the limbs).
Babies with this disease often lack energy, feed and sleep poorly, and startle easily.
A characteristic feature of AADC deficiency is an oculogyric crisis. These episodes may involve unusual rotation of the eyeballs, extreme irritability and agitation, pain, muscle spasms, and uncontrolled head and neck movement. They generally begin later in the day, when a patient is tired, and can last for hours.
AADC deficiency also causes problems with the autonomic nervous system that regulates involuntary body functions like body temperature. Symptoms associated with autonomic dysfunction include droopy eyelids (ptosis), constricted pupils (miosis), excessive sweating, internal temperature instability, nasal congestion, hypersalivation, low blood pressure, reflux, fainting, low blood sugar, and, in extreme cases, cardiac arrest.
Nearly 50% of AADC deficiency patients have movement disorders, such as decreased body movements (hypokinesia), unpredictable involuntary movements (chorea), involuntary muscle contractions that cause repetitive twisting (dystonia), and bulbar weakness that affects the tongue, larynx, pharynx, and respiratory muscles.
Last updated: Sept. 7, 2019
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