Investigating the biological origins of schizophrenia has turned up few solid genetic clues. But a study published in Science [subscription required] in April pointed to one new factor: Patients with schizophrenia frequently have large chunks of DNA added to or missing from their genomes.
Researchers checked the genomes of 150 patients with schizophrenia and those of 268 healthy people, looking for large duplications and deletions of genetic material that disrupted the function of a gene. About 15 percent of the schizophrenics had such mutations, compared with only 5 percent of the people without the disease. In people whose onset of schizophrenia occurred before age 19, the proportion was 20 percent.
Surprisingly, each patient’s mutation was unique, utterly unlike that of any other patient in the study. “Each one occurred in a different spot in the genome,” says University of Washington child psychiatrist Jon McClellan, a coauthor of the paper. “It was counter to most current assumptions.”
When researchers attempt to track down the genetic underpinnings of a disease, they usually find similar mutations that many patients share. But schizophrenia does not fit the pattern, which could help explain why previous findings of apparent genetic correlations have been difficult to replicate.
McClellan and his colleagues found that the mutations were much more likely to alter genes involved in brain development. “What may ultimately turn out to be most important is identifying neurobiologic pathways that, when disrupted, lead to neuropsychiatric illnesses,” McClellan says. “That may offer the best chance for developing more specific treatments.”