Bipolar disorder is often the result of both genetic and environmental factors. Some research estimates the heritability rate of bipolar disorder to be 44%, while others claim it may be as high as 90%.

These figures come from a broad 2021 review of the condition. 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.

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

The exact inheritance pattern of bipolar disorder is unclear, but many gene variations likely combine to increase a person’s risk 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 women who have recently given birth.

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 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. However, a manic episode is all that is necessary for a doctor to diagnose bipolar I disorder.
  • Bipolar II disorder: This 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.

Below are common questions about bipolar disorder.

Is bipolar genetic from the mother or father?

Having a direct relative with bipolar disorder increases a person’s risk of developing the condition. This can be due to both hereditary and environmental reasons. There is no evidence to suggest that the sex of a parent with bipolar alters the risk of their children developing it.

Are people born with bipolar or develop it?

People develop bipolar disorder rather than being born with it. However, some genetic risk factors for developing the condition can be present from birth.

Most experts believe there is a genetic component to bipolar disorder but 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 risk 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.