Schizophrenia, Bipolar Disorder: Gene Link?
Study Shows Family Connections for Bipolar Disorder and Schizophrenia
WebMD News Archive
Jan. 15, 2009 -- The largest study ever to track bipolar disorder and
schizophrenia within families offers evidence that the two psychiatric
disorders share a common genetic cause.
For more than a century the psychiatric community has debated whether
schizophrenia and bipolar disorder were two distinct disorders or were more
Over the course of their illnesses, many patients experience similarities in
certain symptoms characteristic of both, such as manic mood swings in bipolar
disorder and psychosis in schizophrenia.
Recent genetic studies suggest a common genetic cause for the two
conditions. But earlier studies in families have not supported this conclusion,
finding no increase in bipolar disorder in family members of schizophrenics and
Family Links: Bipolar Disorder, Schizophrenia
In an effort to help settle the question, researchers in Sweden linked a
comprehensive national health registry to equally comprehensive hospital
Three decades of registry and hospital data (1973 to 2004) involving 9
million Swedes from 2 million families were analyzed to determine risk for
schizophrenia and bipolar disorder among biological and nonbiological relatives
of patients with one or both of the disorders.
Close to 36,000 people with schizophrenia and 40,500 people with a diagnosis
of bipolar disorder were identified.
The analysis revealed that:
- First-degree relatives (parents, siblings, or offspring) of people with
either schizophrenia or bipolar disorder were at increased risk for both of
- If a sibling had schizophrenia, full siblings were nine times more likely
than the general population to have schizophrenia and four times more likely to
have bipolar disorder.
- If a sibling had bipolar disorder, they were eight times more likely to
have bipolar disorder and four times more likely to have
- Half siblings who shared the same mother were 3.6 times more likely to have
schizophrenia if their half sibling had schizophrenia and 4.5 times more likely
to have bipolar disorder if their half sibling had bipolar disorder. Half
siblings who shared the same father had a 2.7-fold increase in schizophrenia
risk and a 2.4-fold increase in bipolar disorder.
- Adopted children with a biological parent with one of the disorders had a
significant increase in risk for the other.
Shared and non-shared environmental factors also contributed to risk, but
they were less important influences than genetics.
The findings appear in the Jan. 17 issue of the journal The
'Time to Rethink Disorders'
"It is time that we rethink the way we view these disorders," study
co-author Christina Hultman, PhD, tells WebMD. "And it is clear that we
need more genetic studies to help us better understand this shared
In an editorial accompanying the study, Cardiff University dean of medicine
Michael Owen, MD, PhD, suggested that the earlier family studies were far too
small to show the genetic link between schizophrenia and bipolar disorder.