The Chances of Having Hereditary Bipolar Disorder

If you have bipolar disorder and are considering having children, one of the questions you are probably asking yourself is whether you would pass your bipolar disorder on to a child. Is bipolar disorder hereditary? What is the role of genetics in bipolar disorder?

We have known for some time that bipolar disorder can run in families, and now, with genomic sequencing, we are learning about the possible role of genetic factors in the disorder. While the role of heredity is clear from family and twin studies, further research is needed.

The overall lifetime risk of developing bipolar disorder is thought to be somewhere between 1 and 4 percent, depending on the definition, with the average age at diagnosis being 18.

Let's look at what we know about family history and bipolar disorder, and then at what genetic specialists have discovered about the role of individual genes in both bipolar disorder and other mental health disorders.

Bipolar disorder is overall considered to be one of the most heritable of mental health disorders based on a review of family history charts. For example, here are data from a study which found a high family linkage with bipolar disorder:

• A child of one parent with bipolar disorder and one without has a 15 to 30 percent chance of having BP.
• If both parents have bipolar disorder, there's a 50 to 75 percent chance that a child of theirs will, too.
• If you already have one child with BP, there is a 15 to 25 percent chance that another of your children will also have it.
• If one identical twin has BP, there's about an 85 percent chance that the other one will as well. In three other studies, the chance of an identical twin also having bipolar disorder ranges from 38 to 43 percent with that of dizygotic (non-identical) twins being between 4.5 and 5.6 percent.

Many other studies have found that bipolar disorder runs in families, though not all to this degree. Specific aspects of bipolar disorder also appear to run in families including the polarity of illness onset (mania vs depression,) frequency of episodes, the presence of psychosis, suicidality, rapid-cycling, associated alcohol use disorders, panic disorder, and the responsiveness (or lack thereof) to medications such as lithium and other drugs.

The age of onset of bipolar disorder is often younger for those children who have parents or grandparents with a more severe bipolar disorder.

When bipolar disorder runs in families it begs the question: Is the increase in risk related to genetics (specific gene combinations) or the environment?

It appears that both mechanisms are probably at play and contribute to the causation of bipolar disorder.

Though it runs in families, it is harder to define specific genetic risk factors. Studies looking at the genetics of bipolar disorder have failed to find a single gene which is causative (for example, as is the case with cystic fibrosis.) Rather, it appears that there are several chromosomal regions with many genes (polygenic,) each of which has a small effect in raising the susceptibility to the disorder.

Variants in genes such as ANK3, CACNA1C, NCAN, ODZ4 and are thought to increase susceptibility but explain only a very small percentage of the genetic risk. In addition, the majority of people with these "at risk alleles" do not have bipolar disorder.

A separate issue that has been noted with our newer understanding of genetics is that genetics may play a role in how a person responds to medications for bipolar disorder. For example, those with two inactive copies of the CYP206 gene may be poor metabolizers of drugs such as risperidone and aripiprazole. As noted above, how much a person responds to drugs such as lithium may run in the family.

In looking at genetic susceptibility, it has been noted that there is overlap between gene variations noted with bipolar disorder and schizophrenia, schizoaffective disorder, and depression.

Knowing that there is an increased risk of bipolar disorder in children of those with bipolar disorder, should parents with the disorder have children?

This is a question that doesn't have a right or wrong answer. There are many medical conditions which may have a hereditary aspect. In addition, there is not a single gene or gene sequence that "guarantees" a child will develop bipolar disorder.

It's important to note that nothing says that having a child who does develop a mental health disorder will not be a wonderfully fulfilling experience.

Individuals must decide for themselves that is best for them and their family. Knowing you have a family history, however, can be very helpful in monitoring your child should she exhibits any signs or symptoms in order to recognize the condition before an episode of mania is occurring.

It seems clear that there is a genetic role in the development of bipolar disorder, but this role appears to be polygenic (controlled a little bit by many different genes) and very complex. In other words, there is not a single or even several gene variations which cause bipolar disorder, rather, a diverse combination of genes which may increase a person's susceptibility to developing bipolar disorder.

A family history of the disorder is not a reason to put off becoming a parent. You may wish to learn about the red flags for bipolar disorder in children, and the different forms of the disorder.