Parents of children with autism are more likely to have some of the traits associated with autism than parents whose children don't have the disorder, according to a new study.
Among families in the study, those in which both parents scored highly on a test of autistic traits had an 85 percent increased risk of autism in their children, the researchers said. And among families in which one parent had a high score, the risk rose by 52 percent, compared with families in which the parents had lower scores.
Some of the traits that the researchers found to be more common in the parents of kids with autism included subtle difficulties with social skills, a tendency to isolate themselves from other people and repetitive thinking, said study author Dr. John N. Constantino, a professor of psychiatry and pediatrics at the Washington University School of Medicine in St. Louis.
Having traits of autism is different from having the condition itself. For example, autism is usually diagnosed in the 1 percent of people who score the highest on the test the researchers used in their study, whereas among the parents in the study, those whose children had an increased risk of autism scored in the top 20 percent of people taking the test, the researchers said.
"We already knew that the offspring of parents with higher autistic trait scores had significantly higher autistic trait scores than the rest of the general population — what we did not know was whether higher scores in parents could actually raise risk for clinical-level autistic syndromes," Constantino said. "Now, we know." [Beyond Vaccines: 5 Things That Might Really Cause Autism]
Previous research has also shown that the siblings of children with autism who don't have the condition themselves still tend to have more autistic traits than the siblings of kids without autism.
In the new study, published online June 18 in the journal JAMA Psychiatry, the researchers examined data from 256 children with autism and almost 1,400 children who did not have the disorder. The investigators also analyzed data from more than 1,200 mothers and 1,600 fathers of the children.
The people in the study were part of the Nurses' Health Study II, which has been gathering health information from more than 116,000 nurses since 1989.
The researchers also found that, if one parent scored highly on a test for autistic traits, the other parent was more likely to score highly, too. People seem to select partners who share personality traits, the researchers said.
The researchers said they are not sure why such traits occur in some parents, but they noted that these traits are common in the general population, Constantino said.
It is possible that there are advantages to having certain traits, such as a sharp focus on details, he said.
About 1 in 68 children in the United States now have autism, according to a March report from the Centers for Disease Control and Prevention. This is nearly 30 percent higher than the rate of 1 in 88 children that the CDC reported in 2012. The disorder is almost five times more common in boys than in girls; 1 in 42 boys, and one in 189 girls, have autism. The exact causes of autism are not known.
The new study shows that "subtle autistic traits [in parents] raise risk for clinical autism [in their children]," Constantino said. Moreover, it shows that parental traits can add up, in a sense, and contribute to an increased risk of clinical autism in the children, he said.
Therefore, the new research suggests that, although autism can occur in some families as a result of new mutations arising in a child, in other families, "it is the accumulation of multiple susceptibility variants … that may be responsible for autism," he said.
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