What Is Aromatic L-Amino Acid Decarboxylase (AADC) Deficiency?
AADC deficiency is an ultra-rare genetic disorder. It affects how your cells send signals to each other.
People born with this condition don’t make enough aromatic l-amino acid decarboxylase (AADC). That’s an enzyme that helps your brain and nervous system work. Babies and kids with AADC deficiency have developmental delays, weak muscle tone, and movement disorders. They can get other symptoms, too, like droopy eyelids, stiff muscles, and stomach problems.
AADC helps your body make serotonin and dopamine. These are "chemical messengers" called neurotransmitters. Without enough AADC, you don't have enough neurotransmitters to send signals through your nervous system. That makes it hard to control your body, especially your head, face, and neck. It can also affect things like your blood pressure, heart rate, and body temperature.
Signs of AADC deficiency occur early in your baby’s life. There isn’t a cure, but treatment might help manage their symptoms.
It’s OK to ask for help as you or your child deals with this lifelong condition. Tap into your health care team, friends, and family, or find others going through the same thing. A support network can be a big help.
Some people inherit genes with random changes, or mutations. You get AADC deficiency when that happens to your dopa decarboxylase (DDC) gene, which tells your body how to make AADC. You get a copy of the gene from both of your parents. But this disorder is recessive. That means the gene in each parent has to mutate for you to get AADC deficiency.
You’re called a carrier if you have only one copy of the DDC mutation. If you have a child with another carrier, here’s what happens:
- There’s a 25% chance your child will have AADC deficiency.
- There’s a 50% chance your child will be a carrier. They likely won’t have any symptoms.
- There’s a 25% chance your child will have two unchanged copes of the DDC gene. They won’t have AADC deficiency, and won’t be a carrier either.
AADC deficiency is just as likely to show up in males and females. So far, it’s found most often in people of Chinese, Taiwanese, or Japanese descent, followed by people who are Caucasian. It's extremely rare. We know of about only 150 cases to date.
Signs of AADC deficiency are likely to show up when your baby is first born or a few months later. Some symptoms can be mild. Others are serious. Your child might have more symptoms later in the day or when they’re tired. Sleep may help them feel better.
Here are the most common symptoms:
Hypotonia. This is the medical term for weak muscle tone. Someone with AADC deficiency may not be able to hold up their head and torso on their own. Your baby might go limp when you hold them. Your doctor might call this floppiness.
Developmental delays. Your child might fall seriously behind on certain milestones. They might not walk or talk. If they do, those actions will happen a lot later than for other kids.
Oculogyric crises. These “spells” or “attacks” can last for seconds, minutes, or hours. They may happen several times a week. Stress and tiredness may trigger them.
When your child has an oculogyric crisis, they can get symptoms like:
- Involuntary eye movements, like rolling the eyes upward
- Serious crankiness or agitation
- Muscle spasms
- A tongue that sticks out
Other movement disorders. Your child’s muscles might move slowly (hypokinesia) or contract repeatedly (dystonia). Their arms and legs might stay in a fixed position for a while.
Gastrointestinal issues. Your child can have a number of digestion-related problems. They include:
- Acid reflux
- Feeding problems (in babies)
- Trouble gaining weight
- Low blood sugar (hypoglycemia)
Autonomic symptoms. AADC deficiency affects the part of your nervous system that controls unconscious bodily functions. You might have symptoms like:
- Droopy eyelids
- Small pupils
- Excess sweating
- Stuffy nose
- Unstable body temperature
- Low blood pressure
- Heart rate problems
- Sleeping problems
- Cardiac arrest (when your heart suddenly stops working)
Behavioral problems. Some kids with AADC deficiency might cry a lot, seem depressed, or have trouble communicating.
Getting a Diagnosis
Your doctor will ask about your child’s developmental history and give them a physical exam. Symptoms for AADC deficiency can seem like other conditions. That includes cerebral palsy, epilepsy, and other genetic disorders. Your doctor might run blood tests or look at your child’s brain with magnetic resonance imaging (MRI) to rule out other conditions.
If your doctor suspects AADC deficiency, your child will need two or more of these tests:
- Spinal tap. A doctor will insert a needle between bones in their spine to get a sample of cerebrospinal fluid. That’s the liquid that surrounds your brain and spinal cord. If your child has AADC deficiency, certain chemicals or substances will be higher or lower.
- Blood test. A lab technician will take their blood through a needle in their arm. They’ll check to see if they have less AADC enzyme activity in their blood.
- 3-OMD test. Your doctor might check your child’s blood for high levels of a substance called 3-0-methyldopa (3-OMD). Sometimes they use a dried blood spot test. That means your child only gets a finger or heel prick.
- Genetic testing. A lab technician will check their blood for changes in the DDC gene. This is usually used to confirm the diagnosis. As a parent and possible carrier, you may need a genetic test too.
Questions for Your Doctor
Write down everything you’re curious about before your appointment. That way, you don’t forget any key questions. Ask your doctor if you can record the conversation so you can listen to it later.
Some questions you might want to ask include:
- What are all of the treatment options?
- What side effects can the drugs that treat the condition cause?
- Can I enroll my child in a clinical trial on gene therapy?
- Will my child need long-term care?
- What complications should I watch for?
- What drugs should my child avoid?
- What nonmedical treatment can help?
- Is there a social worker on the medical care team?
- Do I need genetic counseling?
- How can I find an AADC deficiency specialist?
Your doctor will design a care plan just for your child. That’s because there isn’t one treatment that works for everyone. A mixed approach with medication and other kinds of therapy might help manage symptoms. More research is needed, but experts think people with AADC deficiency might respond better to drug treatment if they start before they’re 2 years old.
Treatment for AADC deficiency includes:
Dopamine agonists. These drugs raise the amount of dopamine in your nervous system.
MAO inhibitors. These lessen the breakdown of dopamine.
Pyridoxine (vitamin B6). It’s thought to help the AADC you do have work better.
Anticholinergic agents. The idea is that these drugs balance out your dopamine and acetylcholine, a chemical messenger in your brain. They might help ease symptoms like excess sweating, movement problems, and oculogyric crisis.
Melatonin. This is a natural chemical your body makes. Supplements might ease sleep problems.
Benzodiazepines. These quiet down your central nervous system. There’s some evidence that occasional use of them can lessen oculogyric crises or dystonia in some people.
Drugs for other symptoms. Your doctor might add medicines to help with your child’s specific symptoms, like a stuffy nose, crankiness, sleep problems, or muscle contractions.
Nondrug therapy. Depending on your child’s symptoms, they might need physical, occupational, or speech therapy.
Gene therapy. This is when doctors replace your nonworking gene with one that works the right way. This kind of treatment looks promising, but it’s not widely available. We need further research before more people with AADC deficiency can get it.
Taking Care of Yourself
Make regular doctor visits. See a neurologist at least once a year. They should have experience with movement disorders or neurometabolic diseases that affect children.
Make an emergency card. People with AADC deficiency should always have certain information with them. That way, if they have a “spell,” people who are nearby can know how to help them safely.
You can include:
- Info on what AADC deficiency is
- Emergency contact numbers
- Dangers to watch for
- Drugs to avoid
Get vaccinated. Kids with AADC deficiency are more likely to get infections, and their bodies may not be able to fight them as they should. Your child and everyone else in your household should get vaccines.
What to Expect
AADC deficiency is so rare that scientists aren’t sure how it’ll develop in each person. Most of the time, it doesn’t get worse as your child gets older. But new symptoms, like joint issues, can show up because of movement problems caused by the condition.
Serious cases can cause life-threatening symptoms. Ask your doctor what to watch for so you know what to do in an emergency.
You might feel stunned when you learn your child has AADC deficiency. But you don’t have to handle the diagnosis alone. It often helps to connect with others who understand what you’re going through. You can find a support community that meets in person or online.
To find the right group, ask your doctor or social worker. They can put you in touch with a condition-specific or general support group. You can also look for resources on the websites of AADC Trust or RareConnect.
If you get overwhelmed, it’s OK to reach out to a mental health professional. Your doctor can help you find someone to talk to.