Studies Suggest Genetic Link to Bipolar Disorder

Despite making huge strides in understanding the human genome and linking certain genetic defects to particular diseases, scientists have not been able to fully uncover the cause of bipolar disorder. While many researchers believe there may be genetic as well as environmental factors involved with the onset of bipolar disorder, our understanding of the cause of this condition is not yet complete.

Several studies point to growing evidence that bipolar disorder does indeed have a genetic origin. According to the National Institute of Mental Health, certain genetic defects have been positively attributed to causing particular genetic disorders. For example, a defect in a specific human gene causes cystic fibrosis.1 While researches have been able to link specific genetic defects to physical diseases such as cystic fibrosis, they have not been able to positively identify genes that directly cause mental illness, such as bipolar disorder.

Despite not being able to completely understand the role that genetics plays in bipolar disorder, several interesting studies have suggested that genes can at least a partially be held responsible for bipolar disorder. For example, a study of identical twins found that in approximately 40-70% of cases, identical twins will develop bipolar disorder, whereas another sibling has a lower risk.2 The fact that the twins would both develop the disorder suggests that a genetic link exists, considering that the twins share their genes and have a higher chance of developing bipolar disorder than other siblings.

Further studies provide further evidence for a genetic origin of bipolar disorder. Researchers at Johns Hopkins University discovered that approximately 40% of first degree relatives of bipolar patients also had bipolar disorder.3 A study at Stanford University found that children with at least one biological parent affected by the disorder have a substantially higher risk of becoming bipolar themselves. A staggering 51% of children born to a bipolar parent later develop a psychiatric condition themselves, most commonly bipolar disorder, ADHD or major depression.4 It’s not clear what the link is between bipolar disorder and children developing other psychiatric conditions, but the fact that such large numbers of children are affected suggests strongly that genetics plays a role in mental illness; a role that is not yet fully understood.

One final study, conducted by researchers at the University of British Columbia, provides some of the strongest evidence yet that genetics can indeed play a major role in human behavior. Researchers unintentionally deleted a particular gene in mice they were studying, and these mice became unusually aggressive. The animals maimed or killed their fellow mice for no apparent reason. The particular gene that was accidentally deleted, gene NR2E1, is found on chromosome 6 in humans and has been associated with bipolar disorder. This particular gene produces molecules that regulate and affect other genes, and is believed to play a role in brain development and function. When researchers inserted the human version of gene NR2E1 in the mice, their aggressive behavior stopped and they acted like mice are naturally supposed to.

While not fully understood, the continuation of studies into the role that genetics play in the development of bipolar disorder seems promising. Scientific studies that have followed children and siblings of bipolar relatives and the shocking aggressive behavior of mice lacking a specific gene have confirmed that genetics play at least a partial role in the formation of the condition. Researchers will continue to study the specific nature of the human genome in order to better understand and treat bipolar disorder in the future.

Sources:

  1. National Institue on Mental Health. “Looking at my Genes: What can they Tell Me?”
  2. http://www.nimh.nih.gov/health/publications/looking-at-my-genes-what-can-they-tell-me/index.shtml
  3. WebMD. “Causes of Bipolar Disorder.”
  4. WebMD. “Causes of Bipolar Disorder.”
  5. WebMD. “Causes of Bipolar Disorder.”
  6. Bipolar Disorder Daily News Blog. “Genetic Makeup of Aggression & Bipolar Disorder.” July 9, 2005.