ABSTRACT
The most robust and well-replicated neurochemical finding in this disease is the increase seen in whole-blood serotonin in autistic individuals. The factors influencing WHBS levels in normals include platelet structure and activity, 5-HT synthesis, and monoamine oxidase activity. Differing hypotheses about the hyperserotonemia seen in autism therefore have been related to these three different areas. One method for examining the production rate of 5-HT involves the measurement of the primary 5-HT metabolite 5-hydroxyindoleacetic acid. The dietary precursor of 5-HT is tryptophan, and plasma-free TRP levels are thought to have a major effect on central TRP metabolism and 5-HT synthesis. 5-hydroxytryptophan, the immediate metabolic precursor of 5-HT, crosses the blood-brain barrier and increases central 5-HT availability after oral administration. Interest in 5-HT and autism has also spurred therapeutic endeavors, and a number of treatment studies have been performed. A final provocative line of evidence supporting the indoleamine hypothesis of autism is the finding of 5-HT receptor antibodies in some autistic children.
