Scientists have linked common genetic markers with major psychiatric disorders including autism and schizophrenia, in the largest ever genetic study of psychiatric illness.
The study findings, published in The Lancet, show autism, schizophrenia, bipolar disorder, major depressive disorder and attention deficit-hyperactivity disorder (ADHD), all share common genetic risk factors.
The large genome study, which included more than 33,000 patients and 27,000 controls, found calcium channel activity that regulates the flow of calcium in brain cells could play an important role in the development of all five disorders.
“We’ve spent 100 years separating each disease out, saying each disease has its own signs and symptoms which are clinical,” said Peter Schofield, professor in the school of medicine at UNSW.
“Many many people with the disorders don’t fit neatly into the box, this is starting to explain why.
"It provides some robust proof of the emerging idea that there is a greater overlap and commonality, not uniqueness and disparateness,” Professor Schofield said.
“These are really fundamental findings which challenge the existing way of doing business,” said Dr Ian Hickie, professor of psychiatry at University of Sydney.
Professor Hickie said the calcium channel genes identified were particularly interesting.
“We already have drugs that act on those mechanisms. This gives us the potential to take those into new therapeutics in really interesting ways.”
Professor Hickie said drugs that manipulate calcium channels have had limited success to date.
“This will reinvigorate interrogation of whether medicines that regulate calcium channels can be used across disorders to achieve therapeutic benefits,” he said.
The study authors also believe the research may lead to a significant change in the way mental illnesses are classified.
“Our results provide new evidence that may inform a move beyond descriptive syndromes in psychiatry and towards classification based on underlying causes,” said researcher and Massachusetts General Hospital psychiatric geneticist Dr Jordan Smoller.
The research allows for a whole new diagnostic concept, said Jayashri Kulkarni, professor of psychiatry at Monash University.
“That is, that the major psychiatric illnesses are really a spectrum, not discrete entities. It also revives the nature versus nurture arguments,” Professor Kulkarni said.
She added that it could also knock out the current debate about the next Diagnostic and Statistical Manual of Mental Disorders, commonly known as the DSM, since diagnoses could have a biological basis.
However Assen Jablensky, professor of psychiatry at University of Western Australia, said he was sceptical of a move beyond the present descriptive classification of psychiatric syndromes and “towards a nosology informed by disease cause”.
Professor Jablensky said the genotyping performed captured common genomic variants but missed the multitude of rare variants that are believed to exert much stronger effects on the individual risks of disease.
“The rare variants can only be identified by whole-genome sequencing, which probably will be the next major step in our attempts at unravelling the molecular mechanisms of individual risk or disease,” he said.
Professor Schofield said we are still along way from genetic testing for mental illness.
“Even if we knew a thousand variants that predicted very small risk and put that together, would you be able to make a better diagnosis? We don’t know yet.”