Experts said the study, while not identifying the cause of the disorder, provided a striking demonstration of how new gene-scanning technology can open a new frontier in the quest to understand the biology of mental disorders.

Until now, researchers had focused on finding common and known genetic variations that, when acting in some combination, might increase the risk for schizophrenia. They have had little success. The new analysis, being published Friday in the journal Science, detected extremely rare and unknown mutations that turned up three to four times as often in people with schizophrenia as in those without it.

The findings point scientists to previously unappreciated developmental problems that may help them develop more effective treatments, experts said.

Researchers have tried for generations to understand the biological underpinnings of schizophrenia, which affects 1 percent of the population, causing scrambled thinking and delusions. They have analyzed how drugs prescribed for the disorder affect brain cells. They have run large genetic studies, looking in vain for some shared pattern.

The new study suggests that, if anything, the genetics of the disorder are even more complex than many had presumed. But if replicated, experts said, the study¡¯s results will significantly alter the course of psychiatric research.

"This paper represents a paradigm shift in the way we think about identifying genes in schizophrenia," said Dr. Matthew State, director of the neurogenetics program at Yale University School of Medicine, who was not involved in the research. "That is what the authors say in the paper, and it¡¯s true"

Dr. Samuel Barondes, a professor of psychiatry at the University of California, San Francisco, said the new findings in no way disproved the idea that multiple common variations could act together to increase schizophrenia risk. Studies searching for such dark conspiracies of genes are under way and still promising.