Plasma free tryptophan concentration in autistic children

The plasma free and total tryptophan (TRP) and blood serotonin levels in autistic children were examined simultaneously in order to establish a relationship between these parameters and the pathophysiology of infantile autism. The subjects were 37 autistic children, 28 normal adults and 12 normal children. Quantitative evaluation of the global severity, hyperkinetic behavior and intellectual function was performed by means of the Children's Psychiatric Rating Scale (CPRS-1), the Werry-Weiss-Peters Activity Scale (WWPAS) and the Developmental Quotient (DQ), respectively. The mean total TRP level in autistic children was not significantly different from those in normal children and adults. The mean plasma free TRP level in autistic children was significantly higher than those in normal children and adults. A significant positive correlation was found between the plasma free TRP level and CPRS-1 or WWPAS score in autistic children. Moreover, there tended to be a negative correlation between the plasma free TRP level and DQ. These findings suggest the presence of some defect in the metabolic system for TRP-serotonin in the brain of autistic children.