Researchers believe that bipolar disorder is due to genetic and environmental factors. The role of genetics in bipolar disorder is not entirely understood, but research provides insight into how it influences mental health.

The National Institute of Mental Health estimates that 2.8% of adults in the United States experience bipolar disorder in any given year. In addition, 4.4% of people will experience it at some point during their life.

Experts believe that both environmental factors and genetics play a role in the development of bipolar disorder. People with bipolar disorder often have a family member who also has the condition.

The exact inheritance pattern of bipolar disorder is unclear, but many gene variations likely combine to increase a person’s chance of developing it.

Genes are only one factor in the development of bipolar disorder. Most people with a relative who has bipolar disorder do not have the condition themselves. Even in the case of twins, if one develops bipolar disorder, the other may not.

Some studies suggest that the children of older parents at childbirth are at an increased risk of developing bipolar disorder.

Bipolar disorder genetic risk

People are more likely to develop bipolar disorder if they have a close relative with the condition. Some family-based research suggests that bipolar disorder is 44% heritable. Other studies focusing on twins estimate the heritability to be even higher.

However, scientists do not fully understand the role that genes play in bipolar disorder.

It is important to note that just because someone has a greater risk of having bipolar disorder, it does not mean that they will go on to develop it.

According to the National Library of Medicine, some studies indicate that irregularities in many genes combine to increase a person’s risk of bipolar disorder. The exact way that this occurs remains unclear.

It is likely that just having a genetic predisposition to the disorder is not enough to trigger its development. Some environmental factors appear to play a part in triggering bipolar disorder in susceptible people. These include:

  • Periods of high stress: Examples of stressful events that could trigger symptoms of bipolar disorder include a death in the family or being a survivor of rape, abuse, or another traumatic experience.
  • A traumatic head injury: Concussion or other types of brain injury may cause symptom onset.
  • Alcohol or drug misuse: Substance misuse is common among those with bipolar disorder, and the conditions may sometimes trigger each other.
  • Childbirth: Some research suggests that giving birth may trigger the development of bipolar disorder in new mothers.

There are four subtypes of bipolar disorder, each with similar symptoms. However, the occurrence, duration, and intensity of the symptoms can determine which subtype a person has.

Currently, little information is available about the genetic differences between subtypes of bipolar disorder. However, results from a 2022 study suggest that there are genetic differences between bipolar I disorder and bipolar II disorder. These may cause the two conditions to have different symptoms and respond differently to treatment.

Types of bipolar disorder include:

  • Bipolar I disorder: This causes manic episodes lasting 1 week or more or severe mania requiring hospitalization. If it occurs, a major depressive episode may last 2 weeks or more. A manic episode is all that is necessary for a doctor to diagnose bipolar I disorder, however.
  • Bipolar II disorder: This type is similar to bipolar I disorder but involves a less intense form of mania called hypomania. A person with bipolar II disorder must have a major depressive episode lasting 2 weeks or more preceding or following a hypomanic episode.
  • Cyclothymic disorder: This type causes symptoms of hypomania and depression for 2 years or more, but they do not fit the criteria for truly hypomanic or depressive episodes.
  • Other types: These may involve bipolar disorder symptoms that do not fit into the other categories.

Most experts believe there is a genetic component to bipolar disorder, but they do not fully understand the specifics. They also think these genetic variations must interact with environmental factors to trigger symptoms.

People with a close relative who has bipolar disorder have a higher chance of developing the condition, though this does not mean that someone will definitely develop it.

People with any concerns that they or a family member are showing symptoms of bipolar disorder should consult a doctor.

Many treatments exist to help people manage their symptoms and maintain their quality of life.