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Scientists open ‘black box’ of schizophrenia by discovering potential genetic cause

January 30, 2016 at 6:41 PM EDT
Medical researchers have discovered a gene that increases the risk of schizophrenia, a mental illness that afflicts more than two million Americans, sometimes causing delusions and hallucinations. Associate Professor of Genetics at Harvard University Steven McCarroll joins Alison Stewart to discuss the findings.

ALISON STEWART, PBS NEWSHOUR ANCHOR: Medical researchers have discovered a gene that increases the risk of schizophrenia, a mental illness that affects more than 2 million Americans, sometimes causing delusions and hallucinations. The finding was first reported this week in the scientific journal “Nature”.

Steven McCarroll, an associate professor of genetics at Harvard University, is the study’s lead author. He joins me now from San Francisco.

Professor, what was the conventional wisdom about schizophrenia prior to this study, and what was the missing piece of research about that brain disorder that scientists were looking so hard for?

STEVEN MCCARROLL, HARVARD UNIVERSITY: Well, there have been hundreds of theories about schizophrenia over the decades, and it has been hard to tell which, if any of those theories was right.

What’s new here say very strong genetic link to a very specific gene, and specific versions of that gene, and understanding of what that gene actually does and how it shapes the wiring of the brain.

ALISON STEWART: So, can you walk us through what that gene does?

STEVEN MCCARROLL: So, this gene, which is called C4, is in the neighborhood of the human genome that has hundreds of immune systems in it. And that region was previously linked to schizophrenia.

What we discovered though when we got to the bottom of it and figured out what gene is propelling the signal is it is a gene, yes, comes from the immune system but it has this night job in the brain and that, in fact, it plays a role in instructing the wiring of the brain by causing synapses, the connections between nerve cells, to be eliminated at particular times in development.

ALISON STEWART: Now, this elimination, that’s a normal occurrence. What you discovered is that it goes farther than that. It goes haywire?

STEVEN MCCARROLL: That’s right. All of us go through lots of synapse eliminations in our teens and 20s, and it involves the product of this gene. But what we believe based on these results is that that process somehow goes awry, and in particular, it may go into overdrive and result in the elimination of too many synapses.

ALISON STEWART: So, what does this information– how does it help us with the diagnosis of schizophrenia and with the treatment of schizophrenia?

STEVEN MCCARROLL: Drugs for schizophrenia today treat just one of the symptoms of schizophrenia, which is the symptom called psychosis, which are the hallucinations and delusions. Those are actually just one of many symptoms of schizophrenia. And if you ask most patients what are the symptoms that most bother them, what they will tell you is it’s the agonizing cognitive decline that many of them suffer in their first decade after diagnosis.

There are no drugs today that address either the cognitive losses in schizophrenia or the emotional withdrawal or the underlying disease.

ALISON STEWART: So, if I’m understanding what you’re say, the idea is this genetic component is a way to identify the disease before you even have to deal with the symptoms.

STEVEN MCCARROLL: Well, the genetics is a way to understand the disease. You know, when we were in school, we learned it’s genetics that we learned was this very simple genetics — big B, little B. It turns out almost no common diseases work that way. They’re shaped by the interplay of hundreds of genes.

And discovering those genes is a way of telling us what those key biological processes are so that you can point drug development toward the right biological processes. But testing for any one of those genes in the absence of that complete understanding doesn’t teach you anything.

So, we don’t recommend that all. The key thing is going to be understanding the disease well enough to develop new medicines and make the same kinds of progress that we’ve seen in cancer over the last 10 or 20 years.

ALISON STEWART: Steven McCarroll, thank you so much for explaining your work.

STEVEN MCCARROLL: You’re welcome.