This is a great test for those with A1298C and especially who are Homozygous A1298C. Neopterin is bad while biopterin is good. If neopterin is repeatedly high, the BH4 is low.

Neopterin is a sensitive marker of cellular mediated immunity. Reduced levels reflect cellular immunity weakening.

Increased neopterin occur with infectious, inflammatory, immune system dysfunction or neoplastic disease evolution.

Excessive neopterin negatively impacts the Nitric Oxide pathway in the body (e.g. excessive peroxynitrite formation and oxidative stress). Neopterin is a useful index of inflammation response associated with immune system activation.

Tetrahydrobiopterin (BH4) is the cellular protection or antidote to neopterin. It helps to alleviate the oxidative damage caused by neopterin induced immune activation. When BH4 is oxidized by neopterin, it forms biopterin.

If neopterin is constantly increased, then there is a possibility that BH4 levels are inadequate.

“The extent of differential between these two pterins could be considered to be an index of deleterious consequences of cellular inflammation. Decreased biopterin relative to neopterin might suggest inadequate antidote protection capability and increased oxidative damage caused by immune activation (in addition to the original cause of the immune system activation). Too much Oxidized Biopterin (Box) relative to BH4 might suggest an inability to recycle the Box back to BH4 and also inadequate total biopterin to deal with the amount of neopterin.”

This would mean the person needs BH4 (Kuvan™ or TetraHyrdoBiopterin) to reduce the neopterin levels. I usually start this at 2.5 mg daily, then slowly go up. BH4 can significantly improve mood and help with depression, anxiety, and insomnia for these patients.

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