The authors present the first report, to their knowledge, of
hyperserotonemia in children with attentional deficit disorder who had
normal intelligence. Hyperserotonemic children had significantly lower
levels of plasma total and protein-bound tryptophan and a higher percentage
of free tryptophan than those with normal serotonin levels. Plasma
kynurenine did not differ, suggesting that the hyperserotonemia is not due
to a blockade of the kynurenine pathway but may reflect on increase in
tissue tryptophan uptake and use.