Scientists believe they have detected the genetic mechanism underlying autistic disorders.
The research findings from three studies in Britain and the US are being compared with the first understanding of the genetic causes of cancer.
The scientists think they have identified genes which affect brain connections.
However, they warn that the findings will not lead to immediate new treatments.
People with autism have an impaired ability to communicate and interact socially, and display narrowly focused attention and repetitive behaviour.
Although a number of genetic variants have previously been implicated in ASDs, the connections have not been clear.
The new research involved screening the DNA of many thousands of volunteers.
It suggests that proteins called cell adhesion molecules, which play a vital role in shaping brain 'wiring' and the way nerve cells communicate, play a key role in autism disorders.
New treatments could now be developed that target these proteins or the genes that provide the instructions for making them.
Two of the new studies were US-led and reported yesterday in an early online edition of the journal Nature.
The third was conducted by British scientists at Oxford University in England and appears in the journal Molecular Psychiatry.
The largest investigation, conducted in the US, involved analysing the DNA of almost 13,000 people including many from families affected by autism.
Read the report in Nature