Common Misdiagnoses of AADC Deficiency

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by Mary Chapman |

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misdiagnoses and AADC

Only about 100 cases of aromatic l-amino acid decarboxylase (AADC) deficiency are reported in scientific literature globally. This is partly because some individuals are wrongly diagnosed with cerebral palsy or other neurological conditions.

Here are some reasons for the misdiagnoses that commonly accompany AADC deficiency.

What is AADC deficiency?

AADC deficiency is a genetic neurometabolic disease, symptoms of which usually emerge in early infancy. The cause is mutations in the DDC gene, which carries the instructions for cells to make the AADC enzyme. This enzyme is crucial for the production of two important neurotransmittersdopamine and serotonin, from other molecules. Because of the mutations in the DDC gene, cells fail to produce sufficient levels of dopamine and serotonin, affecting the ability of nerve cells to communicate with each other and the rest of the body. The disease affects many aspects of a person’s life.

The diagnostic journey

Tests to confirm AADC deficiency include measuring dopamine and serotonin levels in the cerebrospinal fluid. Others may involve testing the activity of the AADC enzyme in the blood, and analyzing the DDC gene for mutations.

However, AADC deficiency is difficult to diagnose because its symptoms are similar to those of other disorders, and many physicians are unfamiliar with the disease. Patients may have developmental delays, weak muscle tone, muscle stiffness, and athetosis (involuntary jerking of limbs). Other symptoms can include unusual eye movements, droopy eyelids, and excessive sweating.

Although symptoms often become evident in infancy, an accurate diagnosis may take a long time, and several specialists may need to see your child before they reach a diagnosis. The age range of diagnosis is two months to 23 years.

Conditions with symptoms that mimic AADC deficiency

Disorders with symptoms similar to AADC deficiency include epilepsy, cerebral palsy, mitochondrial disease, and neuromuscular weakness.

There are ways to differentiate among these conditions, however. For example, patients with AADC deficiency have oculogyric crises, which doctors often attribute to seizure disorders. But people with a seizure have abnormal electroencephalogram (EEG) results, while those with AADC deficiency generally do not.

Likewise, magnetic resonance imaging (MRI) results are abnormal in cerebral palsy and very slight in AADC deficiency. Still, dystonia (involuntary muscle contractions), rigidity, and motor development delays in AADC deficiency are commonly misdiagnosed as symptoms of cerebral palsy.

Finally, symptoms of muscle weakness, akinesia (frozen movement), and droopy eyes in AADC deficiency are sometimes wrongly attributed to neuromuscular weakness.

Why is the correct diagnosis important?

The sooner a person receives an accurate diagnosis, the sooner treatment can start.

Identifying the underlying genetic mutations causing AADC deficiency is also key to understanding the nature of an individual patient’s disease and likely outcomes (prognosis).

What can I do to get a correct diagnosis?

If your child has AADC deficiency symptoms, consider speaking with his or her doctor about testing for the disorder. Also, if your child has had multiple tests but you still don’t have a diagnosis, ask your doctor about testing for AADC deficiency.

 

Last updated: Sept. 30, 2020

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