THIS IS SOMEHOW ADVANTAGEOUS?: The evolutionary patterns of certain gene variants associated with schizophrenia shows that many of these genes have been positively selected over time.
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Schizophrenia, the psychotic disorder marked by hallucinations, delusions and cognitive disorganization, affects roughly 1 percent of the U.S. population.* Many of those afflicted, however, also have reduced reproductive fitness, which means they are less likely to pass a genetic profile associated with the condition onto their offspring.
"It's sort of a genetic paradox," explains Steve Dorus, an evolutionary geneticist at the University of Bath in England. "Why is this disease found at such a high prevalence?"
Dorus co-authored a report, appearing in this week's Proceedings of the Royal Society B, about the evolution of genes linked to schizophrenia. After analyzing human DNA from several populations around the world and examining primate genomes dating back to the shared ancestor of both humans and chimpanzees, researchers reached a striking conclusion that several gene variants linked to schizophrenia were actually positively selected and remained largely unchanged over time, suggesting that there was some advantage to having them.
"Schizophrenia can be explained by a lot of individual alleles (variations of genes)," Dorus notes. "There are many different loci that impact the actual manifestation of the disease." Over the past decade, several dozen genes have been identified as potential culprits, and scientists believe that several genes cause disruptions in protein formations predisposing a person to schizophrenia.
For this study, the team, which also included Bernard Crespi, an evolutionary biology professor at Simon Fraser University in British Columbia, and East Carolina University evolution professor Kyle Summers, focused on 76 gene variations most strongly related to schizophrenia. By comparing these combinations with the evolution of other genes known to affect neuronal processes, the researchers determined that 28 of the schizophrenia-associated genes have been evolutionarily preferred in recent years by either Caucasian, Asian or African populations.
"Because it's a such a complex genetic trait … you actually expect there to be some variability from population to population, in terms of what genes are playing a role in the disorder," Dorus says. He notes that he was surprised that the study turned up a positive selection for some of the genes most closely associated to the disease, including DISC1 (disrupted in schizophrenia 1), which is involved in the transport of proteins along the relatively lengthy cell bodies of neurons, among them. "The most important thing is we don't really know what the basis of the selection has been," he says. "It could be due to an entire range of neurodevelopmental processes."
Co-author Crespi says that a number of theories have been floating around regarding the persistence of schizophrenia's genetic underpinnings. One holds that schizophrenia is a "disorder of language" and that the illness is an unfortunate consequence of the development of human speech, expression and creativity. "Whenever you get strong selection, it's like a big plus, and you can drag along a lot of minuses," he says. "You can think of schizophrenics as paying the price of all the cognitive and language skills that humans have—they have too many of the alleles that taken individually…might have positive effect, but together they are bad."
Dorus says the team will now home in on the 28 genes fingered in positive selection in the hope of finding new treatments for the mysterious disorder.
*CORRECTION: Initially, this phrase read "Schizophrenia, the psychotic disorder marked by hallucinations, multiple personalities and cognitive disorganization, affects roughly 1 percent of the U.S. population." The condition of having multiple personalities was incorrectly identified as a signature of schizophrenia.
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7 Comments
Add CommentAnother consideration besides reproductive advantage when trying to account for the frequency of an apparently harmful trait might be described as a genetic "rider". Like some bills brought before a legislature, there may be harmful addenda that nonetheless gets passed on within the main document. A genetic analogy might be that say the gene for intelligence also makes one prone to delusions as an unavoidable consequence. Human ancestors once had the capacity to make our own vitamin C; perhaps losing that faculty was necessary in order to gain another, greater one. Of course, there are so many examples of "poor engineering" in living organisms that there is little excuse for a hypothetical "Intelligent designer", but that's another story--or should I say, "DELUSION"?
Reply | Report Abuse | Link to thisWhen I worked in central asia, with violence and civil war all around, I realized that here was the perfect environment for paranoid schizophrenia. People in Tbilisi told me that the first president, Ghamsakurdia, was a paranoid schizophrenic. Fact is, it can work, and work well, in an evironment where people really are "out to get you" where conspiracy and lies are everywhere, and only a crazy person wouldn't be depressed. It has also been long noted that psychosis declines during wartime.
Reply | Report Abuse | Link to thisLike manic-depression, for most of human history, people with paranoid schizophrenia can do extremely well. It doesn't require that everyone with a characteristic do well, it only requires that some with the characteristic do very, very well. How many kings have been insane? I rather think quite a few. Consider all the reports in our old religious literature also.
Another form of mental dysfunction in the modern era is what we call PTSD. Having spent years in places where everyone is traumatized, after thinking about human history, I have come to the conclusion that it is we, the moderns, that are the strange ones. PTSD, like schizophrenia and manic depression, is a survival promoting adaptation to life in dangerous places.
As I was diagnosed at 17 with schizophrenia by an army psychiatrist, I at least have some personal qualification to talk on the subject.
Reply | Report Abuse | Link to thisIt seems to me that the disease is totally maladaptive as it has hindered my capacity to form long lasting relationships with women. Dismissing them because of what the voices in my head say. Double this unfortunate fact of life with another fact that when I am in a controlled medicated state, and trying to lead an ethical life, any truth telling of schizophrenia will make most women run away. The prospect of a delusional hallucinating mate is not a pleasant one.
Perhaps there is some truth to cognitive skill in languages, and this may manifest itself in my preference for the poetic. I have heard the sterotype over and over that schizophrenics are good at art, and while i have some skills, a lot of schizophrenic art is simply awful.
Anyway, love to read sci american.
any information that you have concerning the relationship between siezure disorders, (probably stress induced, and mild learning disorders would be appreciated. I have been hard put to relate to other people or form close bond except with family. I suspect that one or both parents were autistic in some degree, my brothers are color blind and deslexic, and two sons have learning disabilities that make life hard to manage(mild autism and color blindness.)
Reply | Report Abuse | Link to thisAny information that you may have on the interralationships of these elements between generations would be appreciated. Perhaps you would be able to direct me to further relevant research..thank you very much
Kay Rees
Fairbanks, Alaska
Kaychj@acsalaska.net
New schizophrenia genes are very often the result of damaged DNA in the sperm of older men. This is not evolution, this is degradation of humanity. There is a male genetic biological clock and an advantage is given to offspring of younger men and women in many cases. The older the man the more likely the DNA of his sperm making cells may be damaged and lead to autism, schizophrenia, bipolar, cancer, Alzheimer's, type 1 diabetes etc. in resulting offspring.
Reply | Report Abuse | Link to thisIts strange that when I'm on my medications, I feel less smart. The problem, it seems to me, is that schizophrenics cannot handle their intelligence
Reply | Report Abuse | Link to thisYes, my psychologist says this, that really intelligent people often develop problems because they have multi-track minds and more going on thus greater exposure to chemicals bought on by feelings.
Reply | Report Abuse | Link to thisI know when I am manic I can really feel chemicals moving through my brain and allowing easier generation of ideas by the connection of two seperate ideas or memories.
When I was on Risperidone, I was beautifully behaved, never forgot a thing, but couldn't put two ideas together to make an original idea.
I have had voices too in my head and they really do sound just like people talking in your head. They are not simplistic like a lot of people think. They are complex and I have woken up in the middle of the night to interrupt a conversation between two of them.
They are not just negative, but can be very positive. Mine turned out to be Israeli Army generals who instructed me in various aspects of war strategies. Something I have never been interested in. It really was an extraordinary experience.