-A curious adult from Illinois
April 26, 2007
Schizophrenia is not easy to figure out. The genetics are complicated by the fact that so many different genes can be involved. And you don't need to have changes in all of them to get the disease.
To make matters worse, genes aren't enough. All of the genes found so far just make schizophrenia more likely. To actually end up with the disease, you need some sort of environmental trigger too.
What all of this means is that the genetics of schizophrenia are really complicated. And there may not ever be tests that can tell you for sure if you will develop the disease.
So what do we know? Well, we know that around 1% of the U.S. population has schizophrenia. So it is very common.
We also know that if a close relative like a parent or a brother or sister has schizophrenia, then your chances of getting it are around 10%. And if your identical twin has schizophrenia, your chances of getting it are 50%!
Numbers like these tell us a few things. First, schizophrenia is not all genetic. If it were, then identical twins would always both have the disease. This is because they share 100% of their DNA (meaning they have the EXACT same forms of every gene).
Also, numbers like 10% suggest that more than one gene is involved. If it were a simple one gene disease, the numbers would be more on the order of 25 or 50%.
So genes and the environment work together to cause schizophrenia. How in the world does this work?
To better understand all of this, let's think about a simpler condition. There are genes that make people allergic to peanuts. But the genes don't matter if you've never eaten a peanut.
The symptoms of the allergy only become obvious when an environmental trigger, the peanut, is present. The same thing is true for schizophrenia.
Unfortunately, unlike with a peanut allergy, scientists don't know all of the triggers with schizophrenia. But they know a few, like complications during pregnancy and/or birth. Or certain viral infections or certain street drugs.
The other difference between the two diseases is that more genes are involved with schizophrenia. Right now scientists have found about 10-20 genes.
Of course, we all have these genes. It is just that people with schizophrenia have different versions of these genes. Versions that make them more likely to react to the trigger.
As you'd probably expect, most of these genes are involved in how the brain works. An example of this is the gene neuregulin-1
This gene controls how cells in the brain talk to each other. When certain cells don't work right, they can disrupt the whole communication system of the brain. People with schizophrenia have versions of this gene that can make it not do its job properly.
And there are at least 9 other genes just like this (and probably more). This is one of the reasons making a genetic test for schizophrenia is so hard. That and the fact that you need a trigger too.
Because of all of this, there aren't yet any genetic tests for schizophrenia. At least not any that can say for certain whether someone will get the disease. But someday there may be tests that can tell if someone is at risk.
Think of it as using cholesterol to measure your risk for heart disease. When we get our cholesterol checked and it is high, we know to avoid cheesecake and steak. We can also exercise more.
The same sort of thing may be true for a future schizophrenia test. New genetic tests are being developed so that some day people who have the genes for schizophrenia will know this information. By knowing this, they can try and lower their risk of developing the disease by avoiding potential triggers. This could mean staying away from street drug use or stressful pregnancies.
As scientists discover more of the genes involved in schizophrenia, they may be able to figure out what trigger goes with which set of genes. So someone with a history of schizophrenia in the family may be able to take a series of genetic tests that can help them figure out which triggers to avoid.
Unlike with cholesterol, right now there aren't any medications that can prevent schizophrenia from happening. There is nothing like a statin, which can lower our cholesterol no matter what our genes tell our bodies to do.
But maybe as we understand schizophrenia better, such medicines can be designed and/or discovered. Wouldn't it be cool is someone came up with a medicine like statins for schizophrenia? Then someone could get a genetic test and take a drug to keep from getting schizophrenia.