For several years now, scientists have been testing the hypothesis that one particular hormone, oxytocin, plays a role in autism. It seems logical: After all, this molecule nicknamed the "love hormone" promotes bonding between romantic partners and is one of the main signals involved in childbirth, breastfeeding and helping new mothers form strong bonds with their babies. And social-interaction difficulties are a known characteristic of autism, a developmental disorder that affects one in every 68 kids.
But in the flurry of interest around oxytocin, a related signaling molecule has been largely overlooked. Called vasopressin, it's structurally very similar to oxytocin. Both are small proteins made of nine amino acids each, and the amino-acid sequence is identical at seven of the nine spots in the two hormones. Vasopressin is best known for its role in regulating blood pressure, but it also has social roles, which have mostly been studied in rodents.
Noting the dearth of autism-vasopressin research, a Stanford team decided to study vasopressin levels and social behavior in children diagnosed with autism and controls who had not been diagnosed with autism. Our press release about their study, which was published today in PLOS ONE, explains:
The research team found a correlation between low levels of vasopressin, a hormone involved in social behavior, and the inability of autistic children to understand that other people’s thoughts and motivations can differ from their own. ...
“Autistic children who had the lowest vasopressin levels in their blood also had the greatest social impairment,” said the study’s senior author, Karen Parker, PhD, associate professor of psychiatry and behavioral sciences.
Parker and her colleagues examined "theory of mind," the ability to deduce that others have a mind of their own - and that they may perceive the world differently than you do. It's an important underpinning to forming empathetic relationships with other people. In kids with autism, the lower their vasopressin levels, the worse their scores on a test of theory of mind, the study found. Children without autism did not show this link; they all had pretty good theory of mind scores, whether their vasopressin levels were low or high.
It's worth adding that low vasopressin level did not diagnose whether a child had autism; the hormone's levels ranged from low to high in both groups of children. So autism is not simply a state of vasopressin deficiency. However, the researchers are interested in whether giving vasopressin might help relieve autism symptoms and are now carrying out a clinical trial to test its effects.
The work also provides an interesting complement to oxytocin findings published by the same team last year. In the oxytocin study, the scientists found that children with autism could have low, medium or high oxytocin levels, just like other children. However, oxytocin levels were linked to social ability in all children, not just those with autism.
Based on the new findings, it's possible, Parker told me, that vasopressin is uniquely important for children with autism. She's eager to expand her work in this overlooked corner of brain-chemistry research.
Previously: Stanford research clarifies biology of oxytocin in autism, "Love hormone" may mediate wider range of relationships than previously thought and Volunteers sought for autism drug study
Artwork by Dimka