FIVE psychiatric disorders share a common problem in several faulty genes, according to the biggest study of its kind, published on Thursday.
In the widest trawl of genetic mutations linked with mental disorders, US-led researchers looked through the DNA code of 33,332 people with autism, attention deficit hyperactivity disorder, bipolar disorder, major depressive disorder or schizophrenia.
Their genomes were matched against 27,888 ''controls'', or people who did not have these illnesses, in a bid to spot tiny changes in genes.
The five diseases have common risk factors in flaws on chromosomes 2 and 10 and in two genes that help regulate the flow of calcium in brain cells, the investigators found.
One of the genes, CACNA1C, had been fingered in bipolar disorder and schizophrenia.
The study, published in The Lancet, says the common genes are part of a wider picture and do not by themselves explain the causes of these disorders or why their symptoms vary.
The gene samples examined by the Psychiatric Genomics Consortium came from people all from European ancestry and the results may be different for people of different heritage, it said.
But, it added, the findings are a useful step towards better diagnosis of these illnesses.
Psychiatric disorders are difficult to categorise because symptoms can be contradictory or hazy and little is known about their underlying cause. Environmental factors also play a part.
Previous genome comparisons have found common ground in autoimmune disorders such as arthritis, Crohn's disease and psoriasis.