WebMD Medical News
Louise Chang, MD
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
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:
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
"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.
In an interview with WebMD, Owen called the latest research very strong,
with major implications for how patients are managed.
"When someone receives a diagnosis of schizophrenia it is easy for
clinicians to overlook mood disorder and other symptoms that don't fit with
that diagnosis," he says. "The same is true for psychotic symptoms that
may occur in people labeled with a diagnosis of bipolar disorder."
He adds that it is important for clinicians to recognize that symptoms can,
and often do, change over time.
"Most patients don't fit neatly into categories, and the more questions
you ask the more likely you are to find a combination of psychotic and mood
symptoms," he says.
John H. Krystal, MD, of Yale University Medical Center and the VA
Connecticut Healthcare System, agrees.
He tells WebMD that psychiatry has long struggled with "a gray zone"
of patients who do not neatly fit into the categories of bipolar disorder and
He adds that the new research could have major implications for the
development of new treatments for the psychiatric disorders.
SOURCES:Lichtenstein, P. The Lancet, Jan. 17, 2009; vol 373: pp 234-239.Christina M. Hultman, PhD, associate professor, department of medical
epidemiology and biostatistics, Karolinska Institutet, Stockholm, Sweden.Michael J. Owen, MD, PhD, dean of medicine, Cardiff University, Wales.John H. Krystal, MD, professor of clinical pharmacology; deputy chairman for
research, department of psychiatry, Yale University Medical School, New Haven,
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