(RxWiki News) Mental disorders can be passed down through families. The individual factors of each disorder may be the important thing to pay attention to rather than the disorder itself.
A recent study found that mania (abnormal euphoria or overactivity) and depression may be genetically passed on independently of each other.
The researchers concluded that these two major defining factors of bipolar disorder might be separate symptoms that have two different pathways and not two different levels of the same symptom.
"Talk to a psychiatrist if you have a family history of mood disorders."
The lead author of this study was Kathleen R. Merikangas, PhD, from the Genetic Epidemiology Research Branch of the Intramural Research Program at the National Institute of Mental Health, Bethesda, Maryland.
The study included 447 people — 62 people with Bipolar I, 66 people with Bipolar II, 166 people with major depressive disorder, and 157 people in the control group.
Bipolar I is characterized by manic and depressive episodes lasting a week or longer, symptoms often severe enough to warrant hospitalization, and moods that are wildly different from a person's normal behavior.
Bipolar II is characterized by shifting depressive and hypomanic (not full-on manic) episodes, with no full-blown manic behaviors.
Major depressive disorder (MDD) is characterized by depression that prevents a person from functioning normally.
The researchers then used information on 2,082 parents, siblings, and/or children (first-degree relatives) of the participants. There were 246 relatives of the Bipolar I group, 311 relatives of the Bipolar II group, 726 relatives of the MDD group, and 799 relatives of the control group.
Interviews were conducted with the participants, first degree relatives (if alive), and second and third degree relatives to get a family medical history. Each participant had an average of one sibling and one child interviewed. Second and third degree relatives were interviewed if the first degree relatives were dead.
Only 2 percent of the control group's relatives had Bipolar I, 2 percent of them had Bipolar II, and 15 percent had MDD.
Out of the Bipolar I group's relatives, 21 percent had Bipolar I, 5 percent had Bipolar II, and 26 percent had MDD. This meant that the participants with Bipolar I had 8.4 increased odds of having a relative with Bipolar 1, 1.79 increased odds of having a relative with Bipolar II, and 1.34 increased odds of having a relative with MDD.
The researchers also found that 6 percent of the relatives of the Bipolar II group had Bipolar I, 5 percent had Bipolar II, and 31 percent had MDD. Therefore, the participants with Bipolar II had 1.61 increased odds of having a relative with Bipolar I, 2.55 increased odds of having a relative with Bipolar II, and 1.43 increased odds of having a relative with MDD.
The relatives of MDD group reported that 3 percent had Bipolar I, 4 percent had Bipolar II, and 30 percent had MDD. The researchers determined that the participants with MDD had 1.07 increased odds of having a relative with Bipolar I, 1.84 increased odds of having a relative with Bipolar II, and 2.26 increased odds of having a relative with MDD.
However, the researchers found that the only statistically significant associations were for Bipolar I participants having relatives with Bipolar I, MDD participants having relatives with MDD, and Bipolar II participants having relatives with MDD.
In addition, the findings showed that there were 8.27 increased odds of mania being passed between participants and relatives, and 2.45 increased odds of major depression being passed between participants and relatives.
There were no significant associations found for hypomania between participants and relatives, or for mania, hypomania, or major depression being passed between participants and relatives with different mood conditions.
The researchers concluded that mania and depression are genetically passed independently of each other and therefore represent two separate symptoms that are not different levels of the same thing.
The authors noted a few limitations.
First, the researchers argue that these findings are not applicable to the general population with mood disorders — especially people with co-occurring bipolar disorder and psychosis. Second, the interview method allowed for underestimation of the rate of disorders among the participants' relatives.
Third, not every relative could be interviewed. Last, mania and depression are not always considered separately in treatment and therapy.
This study was published online ahead-of-print on October 15 in Molecular Psychiatry.
The Intramural Research Program of the National Institute of Mental Health provided funding.