Using one of the largest-ever samples of post-mortem brains, scientists have identified significant differences in gene expression in two specific regions of the brain—the subgenual anterior cingulate cortex (sACC) and amygdala—in patients who had bipolar disorder. Their findings suggest that this condition may stem from chemical and structural changes in brain cells that affect how they communicate with each other.
The work was led by researchers at Johns Hopkins’ Lieber Institute for Brain Development. The findings, published this week in Nature Neuroscience, represent the first time that researchers have been able to apply large-scale genetic research to brain samples from hundreds of patients with bipolar disorder (BD). They used 511 total samples from 295 unique donors.
“This is the first deep dive into the molecular biology of the brain in people who died with bipolar disorder—studying actual genes, not urine, blood or skin samples,” said Thomas Hyde of the Lieber Institute and a lead author of the paper. “If we can figure out the mechanisms behind BD, if we can figure out what’s wrong in the brain, then we can begin to develop new targeted treatments of what has long been a mysterious condition.”
Bipolar disorder is characterized by extreme mood swings, with episodes of mania alternating with episodes of depression. It usually emerges in people in their 20s and 30s and remains with them for life. This condition affects approximately 2.8% of the adult American population, or about 7 million people. Patients face higher rates of suicide, poorer quality of life, and lower productivity than the general population. Some estimates put the annual cost of the condition in the U.S. alone at $219.1 billion.
While drugs can be useful in treating BD, many patients find they have bothersome side effects, and for some patients, current medications don’t work at all.
In this study, researchers measured levels of messenger RNA in the brain samples. They observed almost eight times more differentially expressed gene features in the sACC versus the amygdala, suggesting that the sACC may play an especially prominent role—both in mood regulation in general and BD specifically.
In patients who died with BD, the researchers found abnormalities in two families of genes: one containing genes related to the synapse and the second related to immune and inflammatory function.
“There finally is a study using modern technology and our current understanding of genetics to uncover how the brain is doing,” Hyde said. “We know that BD tends to run in families, and there is strong evidence that there are inherited genetic abnormalities that put an individual at risk for bipolar disorder. Unlike diseases such as sickle-cell anemia, bipolar disorder does not result from a single genetic abnormality. Rather, most patients have inherited a group of variants spread across a number of genes.”
“Bipolar disorder, also known as manic-depressive disorder, is a highly damaging and paradoxical condition,” said Daniel R. Weinberger, chief executive and director of the Lieber Institute and a co-author of the study. “It can make people very productive so they can lead countries and companies, but it can also hurl them into the meat grinder of dysfunction and depression. Patients with BD may live on two hours of sleep a night, saving the world with their abundance of energy, and then become so self-destructive that they spend their family’s fortune in a week and lose all friends as they spiral downward. Bipolar disorder also has some shared genetic links to other psychiatric disorders, such as schizophrenia, and is implicated in overuse of drugs and alcohol.”
He added that, “Because society values manic productivity, BD is often not seen as the terrible disease it is. But it can be a tragic affliction.”
