Background: Tryptophan is an amino acid, which is responsible for the production of serotonin in the body. Lower levels of tryptophan may play a role in pediatric disorders. In this work the urinary level of tryptophan in autistic and healthy children was compared.
Material/Methods: The samples of urine were taken from 33 autistic children (10 on a restricted diet of gluten and casein free and 23 no diet) and 21 healthy children. The level of tryptophan was determined by gas chromatography/mass spectrometry (GC/MS). In this method tryptophan was derivatized and extracted simultaneously. The method was validated.
Results: Significantly lower relative urinary levels of tryptophan were obtained for both autistic children with a restricted diet 1.98±1.17 µg/mL (mean ±SD) and autistic children without a diet 7.44±1.33 µg/mL (mean ±SD) compared to healthy children 14.24±2.01 µg/mL (mean ±SD). The method has a limit of quantification (LOQ) of 0.15 µg/mL and a lower limit of detection (LOD) of 0.04 µg/mL for tryptophan in urine.
Conclusions: This method is precise and sensitive for the detection of low concentrations of tryptophan and can be applicable to monitoring its level in human urine. Children with autism have a higher deficiency of tryptophan than the control group of healthy children. Lower levels of tryptophan may lead to the worsening of autistic symptoms such as mild depression and increased irritability.

Keywords: Sensitivity and Specificity, Reproducibility of Results, Reference Standards, Limit of Detection, Gas Chromatography-Mass Spectrometry - methods, Child, Case-Control Studies, Calibration, Autistic Disorder - urine, Serotonin - biosynthesis, Time Factors, Tryptophan - urine