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10 SCIENTIFIC AMERICAN MIND Apr i l/May 2006

Loneliness Predisposed

If you feel lonely persistently, blame it partly on your genes. In a survey of 8,387 siblings, 48 percent of identi-cal twins and 24 percent of fraternal twins reported similar levels of mod-erate to extreme loneliness, with much higher agreement than sib-lings who were not twins. The results come from a 12-year study done in the Netherlands by psychologists at Free University and the University of Amsterdam and at the University of Chicago.

The fi ndings, along with ongoing investigation of a satellite of proximal genes on chromosome 12, suggest that some individuals have a genetic vulnerability to feelings of loneliness. Such a propensity should not, however, be thought of as an immutable trait, such as eye color, says psychology professor John T. Cacioppo of the University of Chicago. Rather the genetic bent should be viewed as a risk factor that makes certain individuals more sensitive to environmental factors that can cause loneliness.

Cacioppo believes that genetically based

loneliness could have played an evolutionary role, giving humans an incentive to socialize and share resources. “Loneliness is a signal, just like pain, that something is wrong,” he says. “It motivates you to do something. And the reward associated with that ... motivates the maintenance of those relationships, which is critical to our survival.”

Because loneliness is associated with medical conditions such as elevated blood pressure, knowing your inherited predisposition to it could allow you to make better health decisions. For instance, “you might not take that promotion that requires you to move across the country and leave friends and family behind,” Cacioppo notes. —Michael J. Battaglia

Stem Cells Cause Cancer

Stem cells are vital throughout life because they can devel-op into specialized tissue. Recently, however, scientists have discovered that damaged or altered stem cells may be the driving force behind some kinds of cancer when their specialization takes a malignant turn for the worse.

Stem cells were fi rst identifi ed in leukemia in 1997. Since then, they have been found in breast cancer and certain brain tumors, including glioblastoma multiforme, the most aggressive brain malignancy in adults. Although it was widely thought that most cells in a tumor could cause it to grow, researchers now believe that in some cancers, a small population of stem cells gives rise to all the other cells. When tumor cells are transplanted into experimental mice, only the stem cell variety spurs new cancer growth.

Neural stem cells normally develop into neurons, glia and other cell types. Stem cells found in brain tumors are similar but have genetic mutations that lead to uncontrolled growth. Harley Kornblum, director of the Neural Stem Cell Research Center at the University of California, Los Angeles, is searching for drugs that might inhibit or kill tumor stem cells. Because there are many kinds of brain cancer, Kornblum cautions that they must be approached

individually. “We don’t think there’s a one-size-fi ts-all” mechanism, he says, pointing out that one type of brain tumor called medulloblastoma is caused by “external granule” cells.

Nevertheless, because stem cells activate their genes differently than other cells do, doctors may be able to use genetic analysis to assign more effective treatment to certain patients. Scientists are now focusing on methods to block the unique pathways by which cancer stem cells regenerate, because it seems clear that the stem cells must be eradicated to stop tumor growth. If they succeed, less destructive chemotherapy or radiation, or other treatments, may be possible. —Kaspar Mossman

Individuals prone to

loneliness might decide to not move

far away from family and friends.

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Brain cancer stem cells (left) differentiate into adult tumor cells (right).