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What is AADC deficiency?

Aromatic L-amino acid decarboxylase (AADC) deficiency is a very rare genetic disorder that affects a child’s muscles and how they develop

Watch this short animation to learn more about what causes AADC deficiency and the common signs and symptoms of the condition.

AADC deficiency is a rare, inherited condition.

It affects the child’s nervous system…

…and prevents normal childhood development, including movement, eating, speech and mental ability.

AADC deficiency is caused by a change, known as a mutation, in a gene called DDC or dopa decarboxylase.

Mutations in this gene means that the body can only produce a small amount of the AADC enzyme.

The lack or deficiency of AADC affects the body’s production of critical, natural chemicals, called serotonin, dopamine, adrenaline and noradrenaline.

These chemicals act as messengers sent between the cells in the nervous system.

But, without a functional messaging system, important processes in the body are impacted, leading to symptoms that limit the activities of daily life.

The symptoms of AADC deficiency can vary from one child to another, but most affected children show symptoms in the first few months of life.

The most common symptoms include: Low muscle tone – also known as hypotonia or ‘floppy muscles’.

Delays in development – such as the ability to lift and control the head, say words, sit or stand without support, and walk.

And movement problems – especially sudden episodes of eye movements called oculogyric crises. During an episode, the eyes suddenly roll upwards involuntarily.

These episodes can last from a few seconds to hours and can happen several times a day or several times a week.

Involuntary movements, such as contracting muscles, may also happen at the same time.

Children with AADC deficiency may also show signs of: Other involuntary movements, such as sudden jerking, flailing or twisting, excessive sweating or crying, drooling, drooping eyelids, a stuffy or runny nose, irritability, problems with digestion and feeding, sleeping problems, and epileptic seizures.

If you suspect your child has AADC deficiency, ask your child’s doctor for more information about the disorder and testing.

Early, accurate recognition of AADC deficiency can help improve the care and support these children need.


What are the signs and symptoms of AADC deficiency?

AADC deficiency can cause a range of different symptoms, including:

  • Floppiness (also known as low muscle tone or hypotonia)
  • Delays in development
  • Involuntary eye movements (also known as oculogyric crises)
  • Multiple symptoms associated with bodily functions such as excessive sweating, runny nose or droopy eyelids 

Find out more about the signs and symptoms of AADC deficiency or listen to our podcast “What is AADC deficiency?”

What is a genetic disorder?

  • Genetic disorders are caused by a change in a person’s DNA
  • DNA is a molecule that contains each person’s unique genetic information
  • Some genetic disorders, like AADC deficiency, are caused by changes in the DNA of a single gene
Understanding changes in your genes
  • Genes are small sections of DNA and are found in each cell of the body
  • They contain instructions for making proteins and enzymes that can influence everything from the colour of your hair, skin, and eyes, to how your body functions
  • Sometimes, alterations in your genes can mean that the proteins do not work properly or are not produced at all 

What happens in AADC deficiency?

  • A gene called dopa decarboxylase (also known as DDC) is required to make an enzyme called AADC
  • AADC helps the body to make a molecule called a neurotransmitter, which is used to send messages between nerve cells (called neurons) in your nervous system
  • The nervous system sends messages throughout your body, helping to control many of your body’s functions

In AADC deficiency, a change in the DDC gene means the body produces either none or reduced amounts of the AADC enzyme. This means that not enough neurotransmitters are produced, which in turn, means that fewer messages are sent between neurons. This means that the body doesn’t work like it should and leads to the symptoms experienced by someone with AADC deficiency. Because neurotransmitter levels can be very low in people with AADC deficiency, it is known as a neurotransmitter disorder.

What causes AADC deficiency?

  • Because genetic disorders like AADC deficiency are caused by changes in a person’s genes, it is important to understand where our genes come from
  • Our genes come from our parents, and we get one copy of each gene from each parent
  • Each copy may be a healthy working copy or a copy that does not work as it is supposed to (an altered copy)
  • AADC deficiency is, therefore, passed down from a person’s parents – a process known as inheritance
  • For a child to get AADC deficiency, both parents must pass down an altered copy of the DDC gene, meaning the child has 2 altered copies in total

Because both copies of the DDC gene must be altered for a child to have AADC deficiency, it is known as an autosomal recessive disorder.

GL-AADC-0990 | April 2022


Welcome to About AADC

A website for parents and caregivers of children with AADC deficiency, and members of the public interested in the condition. This website has been provided by PTC Therapeutics.

This educational website provides information to support awareness of a rare neurotransmitter disorder called aromatic L-amino acid decarboxylase (AADC) deficiency.