Plasma and urinary levels of biopterin, neopterin, and related pterins and plasma levels of folate in infantile autism

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Abstract
Tetrahydrobiopterin is essential for brain cells to make monoamine neurotransmitters. It has been reported that the concentrations of tetrahydrobiopterin in plasma and urine are low in certain mental disorders and that oral supplements are beneficial. A group of Japanese investigators have been conducting clinical trials of the effect of administration of tetrahydrobiopterin to autistic children and reported that it is beneficial with no significant side effects. We, therefore, initiated a study to assess plasma and urinary levels of tetrahydrobiopterin in infantile autism to see if they are reduced. Besides tetrahydrobiopterin, we also determined plasma and urinary levels of neopterin and monapterin in these individuals in order to evaluate the status of dihydroneopterin triphosphate, a key biosynthetic precursor of tetrahydrobiopterin. Sixteen autistic children and 12 healthy controls were included in this study. Results indicated that the plasma and urinary levels of tetrahydrobiopterin are not statistically different between the two groups and, therefore, no simple explanation for the beneficial effects of administration of tetrahydrobiopterin on autistic children can be offered at the present time. In contrast, plasma and urinary levels of neopterin were depressed (.01<p<.05) and plasma monapterin was also significantly depressed (p<.01) in autistic subjects compared with controls. Levels of other pterins, including folate, were not statistically different between the two groups. The basis for this depression in neopterin and monapterin is unknown. It does not seem likely that this depression could be attributed to a difference in age or T-lymphocyte/macrophage activity. However, further studies are needed to investigate these possibilities.