Oxytocin and autistic disorder: alterations in peptide forms

Background: Oxytocin (OT) is synthesized as a prohormone that is sequentially processed to peptides. These peptides are the bioactive amidated form (OT) and the C-terminal extended peptides, OT-Gly, OT-Gly-Lys and OT-Gly-Lys-Arg, which are designated together as OT-X. As an extension of our previous study finding decreased plasma OT in autism, studies were conducted to determine whether there were changes in OT peptide forms in autistic children. Methods: Twenty eight male subjects (97 ± 20 months; range, 70–139 months), diagnosed with DSM-IV autistic disorder through observation and semi-structured interview, were compared with 31 age-matched nonpsychiatric control subjects (106 ± 22 months; range, 74–140 months). Using OT antisera with different specificity for the peptide forms, we measured plasma OT and OT-X in each group. Results: T tests showed that there was a decrease in plasma OT (t = 4.4, p < .0001), an increase in OT-X (t = 2.3, p < .03) and an increase in the ratio of OT-X/OT (t = 4.5, p < .0001) in the autistic sample, compared with control subjects. Conclusions: The results suggest that children with autistic disorder show alterations in the endocrine OT system. Deficits in OT peptide processing in children with autism may be important in the development of this syndrome.