New genes found associated with schizophrenia
Two groups of researchers have found new gene variants that provide more understanding about schizophrenia. The new genes were discovered by the teams of Dr. Kari Stefansson of Decode Genetics in Iceland and Dr. Pamela Sklar of Massachusetts General Hospital. The genetic variants that the teams discovered substantially increase the risk for schizophrenia but are limited to a narrow populace of those that have the disease. This finding suggests that schizophrenia can be genetically identified by a large number of extremely rare variants as opposed to a few common variants. According to Dr. Stefansson, “What is beginning to emerge is that a lot of the risk of brain diseases is conferred by rare deletions.”
These results follow a finding in March from a team of researchers at the University of Washington in Seattle that discovered that duplications and sparse deletions of DNA are prominent in people with schizophrenia. The accumulation of new findings suggests that natural selection is efficient at removing unwanted genetic mutations from populations but that new mutations associated with schizophrenia regularly occur in populations despite this. The following is an excerpt of an article from the New York Times that reviews the findings:
“We’ve looked for common variants in schizophrenia and get almost nothing,” said Dr. David Goldstein, a geneticist at Duke University and one of Dr. Stefansson’s co-authors. “This means natural selection has done a really good job of purging them away, and we’re left with rare variants, a constant flow of them, as the principal driver of the disease.”
“This may be the case in other brain diseases, too,” Dr. Goldstein said, “because successful cognitive functioning is a highly complex system and there are many independent ways to take it down.”
One obvious way in which natural selection acts against the disease is that schizophrenics have fewer children than others. “The brain diseases are those where we find the biggest evidence for negative selection, “ Dr. Stefansson said, a finding he found surprising because “I would have thought the brain was a luxury organ when it comes to reproductive success.”
Devising treatments for schizophrenia could be more difficult if the disease is caused by subsets of 2,000 rare variants, say, rather than by just 20 common ones. But several experts said it was too early to know what mix of common and rare variants may cause the disease and whether that might affect the search for treatments.