I am a genetic counselor with a PhD in neuropsychiatric genetics. I specialize in helping families who live with psychiatric disorders. From my experience, I know that when someone in a family is diagnosed with a psychiatric disorder like schizophrenia, it can be a very hard thing - for not only the person with the diagnosis, but also for family members. Schizophrenia can be scary for the person who is diagnosed, and for family members it can be really hard to watch a loved one struggle. Because of this, people who have schizophrenia themselves, or who have a loved one with schizophrenia, are often interested in whether there are ways to ensure that their children will not have to struggle with this condition. So, the recent news about a company that is now offering genetic testing to help couples to select embryos that are at lower risk for this condition, amongst others, might be of interest to parents.
There are many ethical issues associated with this topic – some of which are addressed here. But here, I am going to focus on the specific, practical issue of how - before spending money on something like this, it is really important to understand what this sort of testing might be able to tell you, and what it cannot tell you. Let's start with discussing how genetics contributes to development of schizophrenia.
The tie between genetics and health conditions
Some conditions that affect us are caused only by genetics. Sometimes, a single genetic difference is all it takes for a person to have a particular condition. In these situations, it’s relatively simple to use genetic testing to figure out whether or not an embryo will develop into a person who will have that condition. In this case, genetic tests can determine definitively whether the embryo carries the genetic difference that leads to the condition. However, conditions like this are quite rare.
Most human conditions are caused by different combinations of genetic variations and our experiences (or our environment, if you prefer) all acting together. Schizophrenia is one of the conditions that is caused in this way. We know that there are hundreds of different genetic variations that can contribute to the development of schizophrenia, and many of them are so common in the population that we will all have some of them. Individually these genetic variations each makes only a tiny contribution to whether someone develops schizophrenia. For example, in the general population, there is a chance of about 1% for any of us to develop schizophrenia. Having one of the genetic variations that I mentioned above would make your chance look more like 1.01 to 1.1%
But, of course, this naturally raises the question of: “But what if you look at all the genetic variations together, at the same time? Would that give you a better idea of whether or not someone would develop schizophrenia?” And that is exactly what is happening with this new testing that some companies are starting to offer.
What is a polygenic risk score?
When lots of different genetic variations that can contribute to the development of a condition are all looked at together - at the same time - to generate an estimate of the combined risk, it is often called a polygenic risk score (PRS), or just polygenic score. How useful a PRS can be varies according to what condition you are interested in. But, what we know about schizophrenia is that if you take all of the genetic variations we know about, and add them up together it still only explains about 11% of an individual's overall risk for developing schizophrenia. That means that the test provides no information about the remaining 89% of the overall risk for whether or not that embryo would go on to develop schizophrenia. So the test absolutely cannot help you select an embryo that has no risk for schizophrenia; it cannot guarantee having a child who does not go on to develop schizophrenia.
In fact, to give you a sense of the sorts of things that PRS can tell you:
If you took 100 people randomly from the population, on average 1 of them would develop schizophrenia. Ninety-nine of them would not have the condition.
If you took 100 people who scored in the highest 10% of all PRSs for schizophrenia, on average, 3 of them would develop schizophrenia. 97 of them would not have the condition.
If you took 100 people who scored in the highest 1% of all PRSs for schizophrenia, on average, 6 of them would develop schizophrenia. 94 of them would not have the condition.
Examine Your Reasons for Genetic Testing
For people who are thinking about spending money on this test, it is really important to think about the reasons for being interested in this test. In my experience, people are often very motivated by wanting the best for their children and, having seen how schizophrenia can affect people, they are afraid of “passing on bad genes.”
People also often desperately want to have a sense of control - to feel that there are things that they can do to reduce the risk. These are all really important feelings. For anyone considering these options, and struggling with feelings like this, genetic counseling can really help. We have found that even without genetic testing, the counseling that we can provide, and the deeper understanding of how these conditions arise, and what actions can be taken to reduce risk can be really helpful for people.
Polygenic Risk Scores and In-Vitro Fertilization: What to Consider When Using Genetic Testing
How to Protect Your Mental Health When Genetics Make You Vulnerable
Mental Illness and Genetics: Family History, and Protecting Your Mental Health
Jehannine Austin, Ph.D., CGC, is a past president of the National Society of Genetic Counselors and is a professor in the Departments of Psychiatry and Medical Genetics at the University of British Columbia in Vancouver.
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