Thursday, Feb. 26, 2009 | After years of studying people with a rare genetic disorder, researchers at San Diego's Salk Institute for Biological Studies have identified a gene that plays a role in determining our social behavior. The discovery may not only help us better understand how and why we interact with each other, but also be a stepping stone for treatments of depression, anxiety and other social disorders.
Salk neuroscientists Julie R. Korenberg and Ursula Bellugi were able to identify the gene through their study of people with Williams syndrome, a disorder characterized by developmental problems, specific facial features, low IQs and an overly trusting and engaging personality. From a young age, children with Williams syndrome are very polite and crave close social interactions with others.
The unique characteristics of people with this disorder provide a window into the genetics of how we interact socially, said Korenberg, director of the Center for Integrated Neurosciences and Human Behavior at the University of Utah's Brain Institute and Salk Institute adjunct professor. "There isn't another syndrome that shows this kind of behavior," she said.
"So I am like (infamous bank robber) Willie Sutton, who robbed banks because 'that's where the money is.' I study Williams syndrome because that is where small changes in human genes are associated with changes in human behavior."
The discovery, which was published this month in the online edition of the American Journal of Medical Genetics, is being heralded in neuroscience circles for providing a greater understanding of the basic biology of social interactions. "This is major because almost all of the world's problems have to do with inappropriate social interactions," said Sue Carter, a behavioral neural endocrinologist and director of the Brain Body Center at the University of Illinois, Chicago.
"Our economy is sinking because we can't trust each other. Wars are caused by misunderstandings of people's social intentions. What [Korenberg] is doing is dissecting this problem of what is social behavior and where does it exist in our genome?"
Korenberg and Bellugi, director of Salk's Laboratory of Cognitive Neuroscience, have for 15 years focused their research on Williams syndrome, which occurs in one out of every 7,000 to 20,000 live births. People with the syndrome are missing one copy of genes in a very small region of chromosome 7. (Every human has 23 chromosome pairs, and therefore two copies of every gene.)
To get a sense of how small this region of the chromosome is, consider that of the 30,000 or so genes that provide our genetic blueprint, only 25 are incomplete in people with Williams syndrome.
"You wouldn't think it would make a difference," Korenberg said. "Yet it makes a big difference." These 25 genes ended up giving the researchers clues to the neural pathways that not only determine social behavior in Williams syndrome people, but in the rest of the population as well, Korenberg said.
We have long understood that genes help determine our traits and talents, from hair and eye color to how well we throw a ball or play a musical instrument. But since the human genome was first completely mapped earlier this decade, researchers have increasingly found that genes play a role in many of our behaviors. And isolating genes and the behaviors they help regulate is leading to a greater understanding of not only extreme genetic irregularities like Williams syndrome, but also common disorders like anxiety and depression.
Korenberg and Bellugi were led to their discovery by a young girl they encountered several years ago who had many of the characteristics of Williams syndrome, but was not overly sociable like others with the disorder. The researchers compared her genetic map to those of others with the syndrome and were able to determine that a gene, called GTF2I, was intact in the girl, but not in the others. This showed that GTF2I was a gene involved in social behavior.
But since the region of the genome is so small, Korenberg's lab had to first spend years developing a method to see the area under a microscope before the gene could be identified. Using fluorescent light, the researchers mapped 6,000 points of the genome, including the particular region of chromosome 7. Genes were tagged with different colors, thus making it possible to identify genes that were not intact.
To get a sense of what they were doing, think of how a satellite in space might not be able to indentify individual people on a street corner at night, but could if the people were shining bright lights.
Carter, of UIC, is particularly excited about the discovery because it could lead to more breakthroughs in how this gene might regulate neurohormones. Specifically, a hormone (or neurochemical) called oxytocin, which plays a key role in our desire to seek social interactions with others of our own kind, and avoid those who might do us harm. Problems regulating oxytocin might be why people with Williams syndrome are so overly social and trusting that they get themselves in trouble.
A better understanding of how the hormone is regulated in the context of human behavior might also lead to advances in the treatment of a range of disorders, said both Korenberg and Carter. Researchers have found, for example, that people with anxiety and depression had high amounts of oxytocin. Ultimately, the research could lead to a drug that would effectively control the release of oxytocin.
"It will help us better understand how neurons come together to determine levels of anxiety," said Korenberg, who noted that people with Williams syndrome are prone to suffer from anxiety. "One of the most exciting things is that it could provide treatment targets for anxiety."
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