By Amanda Gardner
MONDAY, July 2, 2012 (Health.com) — A family history of schizophrenia may increase the likelihood that a child will develop autism, a new study has found, suggesting the two conditions share some underlying risk factors.
Researchers analyzed data from three large health databases, two in Sweden and one in Israel, and found that a child's odds of developing an autism spectrum disorder (ASD) tripled if he or she had a parent with schizophrenia.
Two of the databases revealed a similar pattern among siblings. Having a brother or sister with schizophrenia increased the odds of ASD 12-fold in the Israeli population and 2.6-fold in one of the Swedish databases (the only one from that country to include information on siblings).
"This shows pretty strongly that there are most likely genetic components that are shared," says Keith Young, Ph.D., director of the neuropsychiatry research program at the Texas A&M Health Science Center, in Temple, who was not involved in the study. "There may be a common biology between the two."
Having a close family member with bipolar disorder—a mental illness that can trigger psychotic symptoms reminiscent of schizophrenia—also upped the risk of autism, although the association wasn't as dramatic.
These findings, which were published this week in the Archives of General Psychiatry, don't imply that schizophrenia or bipolar disorder cause autism in subsequent generations.
Autism is a "really complicated" disorder, and the evidence to date suggests that a combination of genes and so-called environmental factors—some of which may increase the risk of both autism and schizophrenia—are involved, says Patrick F. Sullivan, M.D., lead author of the study and director of the Center for Psychiatric Genomics at the University of North Carolina School of Medicine, in Chapel Hill.
This isn't the first study to show a family connection between autism and schizophrenia. As Sullivan and his colleagues point out, the new findings are in line with those of a 2005 study from Denmark that found a three-fold increase in autism risk among the offspring of parents with a history of schizophrenia-like psychosis.
"When we start to see basically the same results in different studies and different places at different times, the data becomes a lot more believable," Sullivan says. "I think we need to reconsider the basic split between these disorders."
Next page: More research could lead to novel treatments
Autism and schizophrenia share certain symptoms, such as a reduced capacity for communication and social interaction, Young says. But autism appears very early in life and schizophrenia generally doesn't emerge until adulthood.
In addition, people with ASDs do not exhibit the psychotic symptoms characteristic of schizophrenia, which can include delusions, paranoia, and hallucinations. According to the latest version of the DSM, children with a diagnosis of Asperger's syndrome or "pervasive developmental disorder not otherwise specified"—two types of ASD—cannot, by definition, also meet the criteria for schizophrenia.
The new study may spur doctors to look anew at the links between schizophrenia and ASDs, Sullivan says. In the future, he adds, a better understanding of the overlap between the two conditions could open the door to more precise diagnoses, and therefore more targeted treatment.
That scenario is still a long way off, however. Although scientists have identified a handful of genetic mutations that are linked to schizophrenia as well as autism, the role that specific genes and environmental factors play in the disorders is still largely unknown.
In the shorter term, renewed interest in the shared risk factors for autism and schizophrenia could lead to novel medication strategies, says Young, who is also the chair of an advisory board on brain-tissue research at Autism Speaks, an advocacy organization headquartered in New York City.
"I think these findings will encourage researchers to take a second look at drug therapies that have been shown to be effective in schizophrenia but have not been intensively studied for use in autism," he says.