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 with that brain disorder that scientists were looking so hard for? >> 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 is 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. >> stewart: you can walk us through what that gene does? >> this gene, which is called c4-4, is in the neighborhood of the human genome, has hundreds of immune systems in it. that region was previously linked to schizophrenia. when we discovered though when we got to the bottom of it it and figured out what geefns propelg the signal is it is a gene, yes, that comes from the immune system but it has this nigh

harvard associate genetics associate steven mccarroll who led the research team. congratulations on the discovery. i was surprised to read that more than 2 million americans have schizophrenia. until your study, we didn't know why those changes in the brain were happening >> that's right. it has been a mystery for thousands of years, really, why schizophrenia arises and how it arises and even at a time in medicine where enormous progress has been made over the last 20 or 30 years in finding new drugs for cancer and cardiovascular illness, there has not been equivalent or even similar progress for illnesses of the brain and it's because we don't know the basic things about why they start >>> so what you discovered is a gene, the c 4a gene that that is a culprit that leads to this pruning that goes awrite in young people's brains. >>-- awry >> that's right. pruning is something that happens to all of us in our teens and 20s. particularly pronounced in the parts of the brain that manage complex information and help us interpret and think about the world that we're in