Researchers have found that there appears to be a common connection between schizophrenia, bipolar disorder, and autism spectrum disorder (ASD). Recent studies have shown that children of parents with schizophrenia or bipolar disorder have a 2.9-fold heightened risk of autism, and a 2.6 to 12.1 elevated risk if a sibling has schizophrenia.
The study was done by Patrick F. Sullivan, MD, and colleagues from the University of North Carolina at Chapel Hill.
Researchers also noticed a similar relationship between bipolar disorder in a first-degree family member and the risk of autism, however the link was not as severe.
These results suggest that although the illnesses are different, schizophrenia, bipolar disorder, and autism have the same root cause—possibly shared DNA sequence, a common environmental factor affecting the entire family, or gene-environmental factors.
"Genetic effects may be more likely given substantial heritability estimates for autism spectrum disorder, schizophrenia, and bipolar disorder, along with evidence for relatively lesser but significant environmental effects," wrote Sullivan and colleagues.
Researchers don't believe all three illnesses should be classified in one psychiatric grouping, but said "it is tenable that these disorders are more similar phenotypically than currently appreciated, and it might prove interesting to re-evaluate the degrees of demarcation between these three disorders."
There is a well-known clinical overlap with schizophrenia and bipolar disorder. As well, autism was formerly referred to as "childhood schizophrenia, because the impaired social interactions and bizarre behavior found in autism spectrum disorder were reminiscent of symptoms of schizophrenia," the researchers noted.
Researchers analyzed three different cohorts to study the relationship between the illnesses. They looked at Sweden's national inpatient and outpatient registries as far back as 1973. These included 25,432 patients with ASD. They also analyzed a registry of autism treatment facilities in the Stockholm area from 1984 to 2007. There were 4,982 autism cases with 49,844 controls. The cohort included a psychiatric assessment database of compulsory military service in Israel, which included 386 cases and 435,311 controls from the 1980s.
In all three cohorts, there was a consistent link between a family history or psychiatric disorders and ASD.