May 3 (UPI) -- Unusually low levels of a hormone called vasopressin, known to cause low social ability in monkeys, has now been linked to similar effects in boys with autism.
Researchers at Stanford University, the University of San Francisco and the University of California Davis explored the effects of differing levels of vasopressin, which helps regulate blood pressure and fluid retention. Their findings were published this week in Science Translational Medicine.
Vasopressin has previously been thought to play a role in social, sexual and nurturing behavior. The hormone also interacts with male hormones, including testosterone, leading researchers to believe it could be involved in autism.
Four times the number of boys than girls have autism, which is prevalent in 1 in 59 American children, according to a report issued last week by the Centers for Disease Control and Prevention.
"Since autism affects the brain, it's really hard to access the biology of the condition to know what might be altered," Dr. Karen Parker, an associate professor of psychiatry and behavioral sciences at Stanford, said in a press release. "Right now, the diagnosis is based on parents' reports of their children's symptoms, and on clinicians observing children in the clinic."
Currently there is no biological test to diagnose autism as researchers have had difficulty studying it because humans and mice often fail to show behavioral changes in response to gene mutations that cause autism in people.
Instead, researchers have looked for autism biomarkers in rhesus monkeys, which have similar social capabilities to humans.
Scientists selected 15 male monkeys -- ranging in age from 1 to 5 years old -- with naturally low sociability and were compared then with 15 monkeys with naturally high sociability. Their research was confirmed with an additional 30 male monkeys.
Two hormones, oxytocin and vasopressin, were measured in the monkeys' blood and in their cerebrospinal fluid. They are involved in a variety of social roles, including parental care and pair bonding.
Oxytocin levels didn't stand out in differences of social behavior between the two groups, but the researchers found less social monkeys had significantly less vasopressin in their cerebrospinal fluid than those in the other group. The levels in blood, however, didn't differ between the two groups.
Researchers also compared vasopressin levels in 14 boys with autism and seven children without autism. The levels were collected from a lumbar puncture for medical reasons and revealed the same difference between as the monkeys -- children with autism had lower vasopressin levels than children without autism.
"What we consider this to be at this point is a biomarker for low sociability," Capitanio said.
The next step, researchers say, is to expand the research to more monkeys to establish more precise measurements, as well as to find if they low levels of vasopressin can be detected in order to predict impaired social ability.
"We don't know if we see really low cerebrospinal fluid vasopressin before you see behavioral symptoms of autism," Parker said. "Ideally, it would be a risk marker, but we haven't studied that yet."