Genetics and Risk (to your child)
(reviewed and minor revisions: 11/2005)
You have learned that bipolar disorder has a genetic component, and you would like to learn more about that risk. If you arrived here without such an introduction, you can backtrack to that section and then return.
Dr. Duffy and colleagues, whose review of this topic Duffy is being "translated" here (any mistakes are mine) , emphasize several factors that modify the basic risk estimates. Assume for the following examples that you have some bipolar disorder, and are asking about the risk your children might have it as well. Please also understand that this kind of predicting of risk is very inexact. For example, below you'll see that Dr. Duffy says if one parent only has it, with no other information to go on, the risk is around 20%. Another expert in this field says 10% for that scenario (Berretini, Medscape 2003), and another website on this very topic says 5%. That's a very big range in risk-estimates for something this important. But, that's the state of the science at this point. Read that other site to get another important viewpoint on this issue.
Thus, before you begin, let me remind you: all of this is an educated guess only. What you are reading about here is a statistical "probability" -- not a forecast, nor a prediction, and definitely not a certainty. As I told a patient today whose kids are 2 and 4 years old: as much as you can, try to relax about this issue until they reach puberty. That's when something is much more likely to emerge. If you don't see anything clearly worrisome until then, try as much as possible to let it go; you can worry all you need, later. You'll find more links for yet more information on bipolar disorder in kids at the bottom of this page. In the meantime:
1. First, you must establish whether your partner's family has anyone with a mood problem. If there is no one known to have such a problem, you will base your estimates entirely on your knowledge of your own family members.
On the other hand, if she or he also has affected family members, you will need to use the same process described below looking at that family line as well. If he/she had multiple affected members, who clearly have bipolar disorder, the highest the risk could go is 70% (because that's the current estimate of risk based on identical twin studies, where if one has it, the other will also have it about 70% of the time). If you or your partner have few affected family members, the risk to your children will be lower than 70%. If you both have many affected family members, say half or more people in each generation (his, his parents', and his grandparents' generations) -- then the risk is closer to 70%. Unfortunately, that vague estimate is as precise as we can be.
2. Now we turn to 4 factors that influence how much risk comes from your side of the family. You can apply these same factors to members of your partner's family as well to try to be more precise than the broad estimate given in step 1 above.
Factor A: Patterns across generations
Try to gather as much information about every single member of your family in your generation (brothers, sisters). Then look at your parents' generation: parents, and aunts and uncles on both mother's and father's side. Finally, look at one more generation: your grandparents; or, if little is known or can be known there, use the generation after yours if there is one (nieces, nephews and any children you already have).
Now look for any patterns there: is there someone affected in each generation? If not, the risk to your children may be considerably less than 20%, because in most clearly bipolar families there is indeed someone with a mood problem in each generation. Does the illness seem to skip a generation and appear only in every other one (another occasional pattern, though not guaranteed to hold up over time)?
Factor B: Age of first symptoms
It looks like the earlier a person has symptoms, the more likely they are to transmit the illness. This has been called "genetic anticipation": in each generation the thing gets worse. There are other illnesses which seem to work like this as well. So if you didn't develop your symptoms until you were an adult, your children may face a lower risk (less than 20%, in our model where you are the only affected parent). On the other hand, if you got your symptoms early, in your teens, you may be more likely to transmit the illness -- sorry to say -- to your kids.
Some of this "anticipation" could obviously be caused without a genetic role at all. Growing up with a parent who has bipolar symptoms is potentially, though not always (for example, it depends on how the other parent is handling all this) a stressful experience for a growing child. Stress seems to make bipolar symptoms emerge. So if your symptoms emerged early, it may not have been because of the genetic cause -- and thus not necessarily passed on to your children either.
How big a factor is this "age of onset" thing? Researchers don't know for sure, but it looks like it may have quite an impact, changing the risk quite a bit. That's pretty fuzzy, isn't it? Put it this way: it seems to be one factor among several, and a significant one at that.
Factor C: "Birth Cohort"
This simply means that if you are pretty young, you are in a generation that's been shown in other research to have a higher likelihood of having bipolar disorder. That's because the illness itself seems to be getting more common. No one knows why, though there are lots of guesses (one of them is that electric light changes our biological clocks; for a fascinating demonstration of that, see the section about biologic clocks, including "dark therapy"). By comparison with factor B above, this factor is much smaller.
Factor D: Gender
Overall, women are more likely to end up with a mood disorder problem than men (statistically). Yes, there is a lot of guessing about why this occurs as well. In pure bipolar I, the full "manic-depressive" version of bipolar disorder, the ration of males to females is 1:1. But in mixed states and rapid cycling, the ration is more like 4:1, women over men.
I heard these ratios several years ago, and hear them repeatedly (Update 11/2005: still hearing the same numbers). They seem to underline the importance of women's reproductive hormones on the bipolar process. Yes, there are many things that might also account for the difference, such as the stresses women face compared to men. But the more I ask women about their hormonal status, the more it seems to connect to the illness picture. Very little is known about this. As I learn more, I'll keep posting it on the Hormones and Mood section of this website.
Now you know about some ways to modify the basic predictions of 20% or (absolute maximum) 70%. There's a bit more in the article by Dr. Duffy and her colleagues, but this is the main stuff that might help you estimate risk.
Before you go, here are two sources of information on the childhood features of bipolar disorder.
1. The Juvenile Bipolar Disorders Research Foundation: http://www.bpchildresearch.org/juv_bipolar/index.html
2. www.bpkids.org: the Child and Adolescent Bipolar Foundation