Bipolar disorder is characterized by dramatic changes in mood, energy and activity levels that impact a person's ability to carry out everyday tasks. The exact cause of the condition is unknown. But now, researchers are one step closer to finding out with the discovery of two new genetic regions that are connected to the disease.
The international research team, led by investigators from Germany and Switzerland, recently published their findings in the journal Nature Communications.
Although the cause of bipolar disorder is unclear, researchers do know that genetic factors play a large part.
"There is no one gene that has a significant effect on the development of bipolar disorder," says Dr. Markus M. Nöthen, of the University of Bonn Hospital in Germany.
"Many different genes are evidently involved and these genes work together with environmental factors in a complex way."
For their study, the researchers obtained genetic data from 2,226 patients with bipolar disorder and 5,028 individuals without the condition. This data was merged with existing data sets and analyzed.
This led to the comparison of genetic material from 9,747 bipolar patients with that of 14,728 healthy individuals - the largest investigation of the genetic foundations of bipolar disorder to date, according to the researchers.
The team says that the search for genes involved in bipolar disorder is like "looking for a needle in a haystack." Dr. Sven Cichon, of the University of Basel Hospital in Switzerland, explains that individual genes make contributions to the disease that are so small, it is difficult to identify them.
However, comparing the DNA of large numbers of bipolar patients with the DNA of large numbers of healthy individuals makes this process easier, as differences between the two groups can be confirmed statistically.
Five risk regions found, two newly discovered
Using their large data collection, the investigators analyzed around 2.3 million different genetic regions, first in the bipolar patients, then in the healthy controls.
- Biopolar disorder affects around 5.7 million adults in the US every year.
- Onset of the disorder usually occurs in late teens or early adult years.
- Children who have a parent or sibling with bipolar disorder are much more likely to develop the illness.
Subsequent evaluation of these regions revealed five risk regions on DNA that are associated with bipolar disorder.
Three of these regions - ANK3, ODZ4 and TRANK1 - have been described in previous studies, although the researchers note that they were statistically better confirmed in this study.
But the other two risk regions - ADCY2 on chromosome five and so-called MIR2113-POU3F2 on chromosome six - were newly discovered.
The research team says the ADCY2 region is of particular interest, as it codes an enzyme that plays a part in sending signals to nerve cells.
"This fits very well with observations that the signal transfer in certain regions of the brain is impaired in patients with bipolar disorder," explains Dr. Nöthen.
The research team concludes that their findings - particularly the discovery of the ADCY2 risk region - provide new insight into the biological mechanisms involved in the development of bipolar disorder.
Dr. Nöthen adds:
"Only when we know the biological foundations of this disease can we also identify starting points for new therapies."
Last year, Medical News Today reported on a study detailing new brain scans that measure blood flow, which could diagnose bipolar disorder in its early stages and differentiate it from depression.