Autism and schizophrenia may be genetic opposites, an evolutionary biologist in British Columbia says.

Bernard Crespi of Simon Fraser University and his colleagues analyzed data on all known genetic variants linked to both conditions.

Crespi thinks that autism and schizophrenia are diametric opposites in how they affect gene activity in specific regions of the brain.

The researchers looked at four regions in the human genome where mutations known as copy number variants can arise — stretches of DNA that contain accidental duplications or deletions. Instead of the usual two copies, one or three copies may be found.

The investigators found deletion mutations in people with autism and duplications in people with schizophrenia, the team reported in this week's online issue of the Proceedings of the of the National Academy of Sciences.

Crespi said the immediate importance of the finding is that if autism and schizophrenia are proven to be opposites, then researchers working on a therapy for one illness may be able to consider new directions for the other.

"The conceptual framework of one disorder will illuminate the study of the other," he told CBC News.

This could be true for both drugs and cognitive behaviour or talk therapy, since drugs working on receptors in the brain could be dialled down for one condition and made to work more for the other.

The findings fit with data from studies of head and brain sizes that show autism is commonly associated with developmentally enhanced brain growth while people with schizophrenia tend to show reduced brain growth.

The copy number variants are very rare events. When they do occur, the odds of getting autism or schizophrenia increase dramatically, Crespi said.