The scientists studied a region of a particular chromosome. That chromosome region is where the DTNBP1 gene is located.
The DTNBP1 gene has previously been associated with schizophrenia, write the researchers. They included Katherine Burdick, Ph.D., of the psychiatry research department of the Zucker Hillside Hospital, which is part of the North Shore-Long Island Jewish Health System.
Burdick and colleagues studied 213 unrelated whites with schizophrenia or a related disorder. For comparison, the study also included 126 unrelated healthy whites who didn't have an immediate relative with certain mental disorders.
Testing Intelligence, DNA
Participants took various tests of mental skills including reading, verbal learning, and word association. The researchers also studied participants' DNA, focusing on six different sequences of the DTNBP1 gene.
Here's an easy way to picture those sequences. Think of a bracelet of beads of various colors. One bracelet might have a sequence of three gold beads, a blue bead, and a red bed. Rearranging those beads would create different sequences on the bracelet.
The sequences studied by Burdick's team work the same way. Of course, those sequences are made of genetic building blocks, not colored beads.
One of those six sequences stood out. It was rare in all participants and was linked to lower scores on the mental tests, the researchers report.
Intelligence Goes Beyond Genes
That particular sequence explained about 3 percent of the variation in test scores in healthy people and about 2 percent of the variation in test scores in participants with schizophrenia or a related disorder.
In other words, the sequence didn't solely explain why some people scored higher than others on the tests, regardless of schizophrenia.
"While our data suggests the dysbindin gene influences variation in human cognitive ability and intelligence, it only explained a small proportion of it — about 3 percent," researcher Anil Malhotra, M.D., says in a news release.
"This supports a model involving multiple genetic and environmental influences on intelligence," Malhotra continues. Like Burdick, Malhotra works in the Zucker Hillside Hospital's psychiatry research department and the psychiatry department of Albert Einstein College of Medicine.
Other researchers who worked on the study are based in Boston at Harvard Partners Center for Genetics and Genomics.
SOURCES: Burdick, K. Human Molecular Genetics, May 15, 2006; Vol. 15: pp. 1563-1568. News release, North Shore-Long Island Jewish Health System.
By Miranda Hitti
Reviewed by Louise Chang, M.D.
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