Aromatic L-amino acid decarboxylase (AADC) deficiency is an inherited condition that affects the communication between the brain and other parts of the body. Among other symptoms, patients experience movement disorders and autonomic dysfunction.

What is myoclonus?

Myoclonus refers to a muscle jerk and is one of the symptoms of the movement disorders that occur in AADC deficiency patients. Everybody experiences involuntary muscle jerks from time to time (hiccups, for example). Most people also occasionally experience muscle jerks when falling asleep. Myoclonus is always involuntary and often described as a mild electric shock.

Myoclonus in AADC deficiency

In AADC deficiency, myoclonus can occur in newborns, and at later stages as the baby grows and during adulthood. Myoclonus may occur at different intensities and frequencies and last a long time, so they may interfere with daily activities such as eating, walking, speaking, and breathing.

Patients with AADC deficiency may also experience seizures that closely resemble non-epileptic muscle jerks. People who are not medical professionals are often unable to distinguish between non-epileptic muscle jerks and seizures.

How does AADC deficiency cause myoclonus?

AADC deficiency is caused by mutations in the dopa decarboxylase gene (DDC) gene. This gene provides the instructions necessary to build the aromatic L-amino acid decarboxylase enzyme, which is involved in the production of the neurotransmitters dopamine and serotonin. Neurotransmitters are signaling molecules that enable the communication between neurons or nerve cells. Mutations in the DDC gene either decrease the production of the aromatic L-amino acid decarboxylase enzyme or reduce its activity. In both cases, the synthesis of dopamine and serotonin is reduced.

The brain sends signals to other parts of the body with the help of neurotransmitters. Nerve cells control muscle movement, among other functions. Insufficient levels of neurotransmitters, such as dopamine and serotonin, can impair the correct communication between the brain and muscles, and thus lead to movement disorders such as myoclonus.


Last updated: Oct. 04, 2019


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