The small study suggests repetitive behaviors characteristic of autism are related to exposure to immune system factors from the mother during pregnancy.

The study builds on research by Judy Van de Water of the University of California, Davis, scheduled to be published in Neurotoxicology, which found IgG antibodies in the mother's blood of children with one type of autism.

"We wanted to take that important finding a step further and find out if IgG exposure during pregnancy could cause the kinds of changes in social interactions or behavior we see in children with autism." study author David Amaral of the University of California, Davis, says in a statement.

Amaral and his research team at the California National Primate Research Center exposed four monkeys to IgG from mothers of children with autism, while four received IgG antibody of typically developing children. Five monkeys received no treatment.

The study, published online in advance of print in Brain, Behavior and Immunity, identified mild, but distinct, behavior characterized by repetitive activities like pacing and twirling in the monkeys prenatally exposed to IgG from autistic mothers.