Background: Autistic Disorder is an early-onset developmental disorder with severe lifelong impact on social functioning, communication, and behavior. There is currently no marker or cure. The pathophysiology and etiology are obscure. Evidence for abnormal gamma-aminobutyric acid (GABA) function in Autistic Disorders is limited. A few case-reports and small studies have reported differences in GABA levels in plasma, platelets, and urine, compared to controls. Further studies on abnormalities of GABA function in Autistic Disorder are warranted.
Material/methods: Plasma GABA levels were measured using a new and sensitive technique, based on gas chromatography/ mass spectrometry, in a small group of youngsters with Autistic Disorder and
Attention-Deficit/Hyperactivity Disorder. Participants were outpatients between ages 5–15, satisfying modern criteria for these disorders.
Results: Elevated plasma GABA levels were found in youngsters with Autistic Disorder. Psychotropic medications did not seem to affect plasma GABA levels in this study. Plasma GABA levels decreased with age.
Conclusions: Elevated plasma GABA levels may be a biochemical marker of Autistic Disorder. This study supports the hypothesis that GABAergic mechanisms play a role in the etiology or pathophysiology
of Autistic Disorder. However, the hypothesis remains unspecified owing to lack of research. Future studies on the clinical associations of seizure disorders, mood disorders, and catatonia in autistic people may provide the necessary data to formulate a coherent theory of
GABA dysfunction in Autistic Disorder. More trials of medication with known or suspected effects on GABA function are warranted.

Keywords: Adolescent, Attention Deficit Disorder with Hyperactivity - blood, Autistic Disorder - blood, Autistic Disorder - etiology, Biological Markers - blood, Child, Child, Preschool, Pilot Projects, gamma-Aminobutyric Acid - blood