Researchers recently broke new ground in finding the genetic causes of mental illness, identifying a specific region in the genome associated with schizophrenia, bipolar disorder, and autism.
An international team, led by geneticist Jonathan Sebat, Ph.D., of Cold Spring Harbor Laboratory, has discovered a mutation on human chromosome 16 that is a potent risk factor.
"This type of genetic variation is called copy number variation," Sebat explains. "It means that instead of having differences in sequence, you have a deletion or a duplication of a whole gene or genomic region. It's not a mutation; it's extra copies of a gene. So the dosage of the gene changes, rather than the sequence."
Specifically, Sebat and his team found that a duplication in copy number variation predisposes someone to schizophrenia and bipolar disorder - and a decrease in CNV is associated with autism.
"Basically, the implication is that the same gene is associated with multiple disorders," say Sebat. "The ways they're disrupted determines how they influence the long-term psychiatric outcome."
He cautions, "This is a slight oversimplification. There is fuzziness there. Duplication is also associated with autism. No matter how you mutate this region, you could get a child with autism or developmental delay. Any mutation in this region can result in a child with a developmental delay."
Others involved in the research include Deborah L. Levy of the Psychology Research Laboratory at McLean Hospital in Belmont, Massachusetts, and the Department of Psychiatry at Harvard Medical School in Boston, who was awarded a NARSAD Independent Investigator grant. The results of this study were published on the Nature Genetics website on October 25, 2009, prior to coming out in the journal.
Applying a New Approach
In their research, the team pioneered a new approach, using a technique called microarray analysis. "We used a gene chip to scan the genome," Sebat explains, "looking for sections that were increased or decreased in copy number. Early on, it became clear that this was an excellent tool for cataloguing the mutations found in anyone's genome.