The findings may one day lead to new treatments for bipolar disorder.
"Treatments that target just a few of these genes or the proteins they make could yield substantial benefits for patients," Francis McMahon, MD, says in a National Institutes of Health (NIH) news release.
First, McMahon and colleagues screened the genes of 975 people from the U.S., including 412 bipolar disorder patients and 563 people without bipolar disorder.
The scientists found 80 gene patterns that were more common in the bipolar disorder patients.
Next, the researchers verified their findings by studying DNA from more than 1,300 Germans, including 679 bipolar disorder patients and 543 people without bipolar disorder.
Bipolar Disorder's Complex Roots
No single gene stood out in the DNA studies. The genes identified by McMahon's team were only modestly linked to bipolar disorder.
"These data suggest that bipolar disorder is ... influenced by many genes, each of small effect," write McMahon and colleagues in Molecular Psychiatry's online edition.
One of the genes that was more strongly associated with bipolar disorder is the DGKH gene, which makes a protein that is sensitive to the bipolar disorder drug lithium.
"Lithium is still the primary treatment for bipolar disorder, but DGKH is a promising target for new treatments that might be more effective and better tolerated," says McMahon.
A person's chance of having bipolar disorder may depend on their bipolar disorder gene profile and environmental factors that interact with genetic risk, the researchers note.
They add that many of the genes they identified are located in DNA regions that have previously been linked to bipolar disorder and schizophrenia.
Because gene patterns may vary among different ethnic groups, the researchers only studied people of European descent. Another study is under way to probe the genetic roots of bipolar disorder in other populations, notes the NIH.