People with autism, a developmental disorder, often find it difficult to interpret facial expressions or maintain eye contact with others. Low levels of vasopressin, a neuropeptide found in the brain, may help explain the social difficulties of children with autism, according to Stanford University School of Medicine researchers.

“Autistic children who had the lowest vasopressin levels in their blood also had the greatest social impairment,” said Dr. Karen Parker, associate professor of psychiatry and behavioral sciences, in a press release. Based on these findings, Parker and her team have begun a clinical trial in which children with autism are treated with vasopressin to reduce their social problems.

Neuropeptides, like vasopressin, are protein-like molecules used by neurons in the brain to communicate with one another. Vasopressin also helps regulate blood pressure. The hormone is structurally similar and closely related to oxytocin, another neuropeptide that's known to play a role in social behavior. In experiments, vasopressin has been shown to improve social cognition and memory in people who do not have autism. Characterized by social deficits and repetitive behaviors, autism affects one in every 68 American children.

For the new study, the researchers examined a social trait known as “theory of mind.” As described by the researchers, this is the ability to understand people have perspectives unlike your own. First, the team verified that vasopressin levels in the blood accurately reflect vasopressin levels in the brain. They did this by measuring blood levels of the neuropeptide and comparing them to cerebrospinal fluid levels in 28 people.

Next, the researchers recruited 159 children between the ages of 3 and 12. Of these children, 57 had autism, 47 were typically developing but with a sibling who had the condition, and 55 were typically developing kids with no siblings with autism. At this point, the children completed standard assessments of their cognitive abilities, social responsiveness, theory of mind, and ability to recognize emotions.

The children also gave blood samples that were measured for vasopressin. Children in each group showed low, medium, and high levels of the neuropeptide. Children without autism, no matter their blood vasopressin level, had similar scores on theory of mind tests.

In the children with autism, though, low vasopressin levels in the blood correlated to low theory of mind ability. In fact, the lower the level, the lower their ability.

Clearly, the data revealed children without autism can have low vasopressin levels and not display social impairment, so autism cannot be explained by a vasopressin deficit alone, the researchers noted. Still, they believe these findings raise the possibility that treating children with autism with vasopressin could reduce their social problems. It’s probable, too, that blood-based biomarkers might “enhance diagnostic accuracy and provide an objective metric for treatment response,” the researchers concluded.

Source: Carson DS, Garner JP, Hyde SA, et al. Arginine Vasopressin Is a Blood-Based Biomarker of Social Functioning in Children with Autism. PLOS One. 2015.