Vitamin B6 (pyridoxine) is a first-line treatment for aromatic L-amino acid decarboxylase (AADC) deficiency. It is often used in combination with dopamine receptor agonists and monoamine oxidase inhibitors (MAOIs).
How does vitamin B6 work?
AADC deficiency is caused by mutations in the dopa decarboxylase (DDC) gene. This gene provides the instructions necessary to build the AADC enzyme. This enzyme performs the last step in the synthesis of the neurotransmitters dopamine and serotonin. Neurotransmitters are signaling molecules that enable communication between nerve cells in the brain and the rest of the body.
A mutation in the DDC gene leads to decreased production of the AADC enzyme or reduces its activity. Consequently, less dopamine and serotonin are produced, which causes the dysfunction of the motor and autonomic nervous system seen in AADC deficiency patients.
Vitamin B6 acts as a cofactor for the AADC enzyme and can increase the activity of the enzyme, leading to the production of more dopamine and serotonin.
Studies for vitamin B6
Although vitamin B6 can increase the activity of the AADC enzyme, a clear clinical benefit has not been shown. No randomized clinical trials have been performed to test vitamin B6’s efficiency for the treatment of AADC deficiency and most case reports show no improvement with vitamin B6 treatment.
One study reported 78 AADC deficiency cases, of which 55 were treated with vitamin B6 at doses ranging from 4 to 81 mg per kg body weight per day. Fifteen patients with a relatively mild form of the disease improved on combination therapy with vitamin B6, dopamine agonists, and monoamine oxidase B inhibitors. Because of the combination of different medications, it is not possible to determine vitamin B6’s direct effect on the improvement of symptoms.
Vitamin B6 therapy may cause gastrointestinal problems, sleeping problems, and motor restlessness (an irresistible urge to move). When used at high doses for long periods, vitamin B6 can also lead to nerve damage.
Last updated: Sept. 23, 2019
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