Australasian Science: Australia's authority on science since 1938

Genetic Overlap in Mental Illnesses

By Stephen Luntz

Genetic variations associated with depression, schizophrenia and bipolar disorder have substantial overlap, indicating possible relationships between the conditions.

“We studied the genetic information of more than 75,000 people using a type of genetic variation called single nucleotide polymorphisms (SNPs),” says A/Prof Naomi Wray of the University of Queensland’s Brain Institute. “A SNP is one of the most common genetic changes, and involves the replacement of a single unit that makes up our DNA with another. Using about a million SNPs measured on each person, we found evidence of increased genetic similarities between people with the same disorder.”

The SNPs studied accounted for around 20–25% of the variation in rates of these diseases, or about one-third of the total genetic contribution. “The rest could be from rarer SNPs or from other genetic effects,” Wray says. “Our research is consistent with the idea that the genetic component is high.”

While the SNPs of someone suffering from a particular condition had more in common with the SNPs of others with the same condition than with people suffering from other diseases, there was considerable overlap between schizophrenia, bipolar disorder and depression.

Initial misdiagnosis of mental illness is common. “I was worried that this could affect our data, so I investigated and published another paper showing that even at common levels of misdiagnosis this could not account for the overlap we observed,” Wray says. She also believes the patients included in the study would mostly have been those with stable diagnoses that are much more likely to have been accurate than initial assessments.

Wray does not anticipate novel treatments for any of the conditions to become available soon as a result of this work. Nor does she think researchers are close to being able to diagnose mental illnesses on the basis of genetics.

“We’ll never get accurate diagnoses from DNA testing alone, but it might eventually help provide a risk strata that could give a more probabilistic statement to use in conjunction with observations of symptoms,” Wray says. “One problem with psychiatric disorders is that we put these binary labels on them. We may find that conditions that are more clinically similar are also more genetically similar.”

The research was published in Nature Genetics and involved more than 300 scientists from 250 institutions.