A group of Harvard scientists say a major leap forward has been made in understanding the biology behind schizophrenia.

Dr. Steven McCarroll and his colleagues analyzed the genomes of 64,000 people, about half of them with schizophrenia, and now believes that the cause of the disorder can be found in a single "neighbourhood" of the human genome, MHC.

"[MHC] has hundreds of genes, most of which contribute to the immune system," McCarroll told On The Coast host Stephen Quinn, adding there had been hints immune system genes were connected to schizophrenia, but it was unclear which ones.

"So for a while, people assumed that this genetic signal was pointing to some virus or critter or something like that, that somehow gets into the brain," he said.

McCarroll said a student in his lab examined long-available data in a new way, and found a molecule connected to the immune system had a second job: it guides the wiring of the brain at certain key times by eliminating certain underutilized synapses — connections between nerve cells in the brain.

One of those key times occurs during the teenage years and the early 20s when people go through a "pruning" of synapses. This is also the age when schizophrenia emerges in most people with the disorder.

"It's always been a mystery: why then? Why not earlier and why not later?" McCarroll said. "On some level, as a model or explanation, this makes much more sense because it connects the disease to a normal developmental process that … in about one per cent of the population, somehow goes awry or out of control."

Dr. Steven McCarroll and his colleagues analyzed the genomes of 64,000 people and now believes that the cause of the disorder can be found in a single “neighbourhood” of the human genome. (http://mccarrolllab.com/)

McCarroll says his hope is this research can lead to new drugs that treat the underlying causes of schizophrenia, instead of merely the most pronounced symptom — psychosis.

However, he admits that such drugs could be years away.

"At least we know where to look," he said. "If you look at the areas where there are lots of effective drugs today, like cancer … there's a biological understanding that made it possible to develop new medicines."

"For illnesses like schizophrenia, we've never had that understanding."

The work of McCarroll and his colleagues was published on Jan. 27 in the journal Nature.

To hear the full story, click the audio labelled: Harvard researchers believe they've found the cause of schizophrenia