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It found several genetic variants commonly associated with ASD, all of them pointing two specific genes found on chromosome 5 which control production of proteins which help cells stick to each other, and make nervous connections.

One variant, linked to a gene called CDH10, was so common - present in over 65% of cases of autism - that the researchers calculated that fixing it would cut the number of autism cases by 15%.

They also linked ASD rather less strongly to a group of about 30 genes which produce proteins that play a key role in enabling brain cells to migrate to correct places, and to connect to neighbouring cells.

Professor Simon Baron-Cohen, an autism expert at the University of Cambridge, said 133 genes had now been linked to the condition, and much work was needed to piece together how they interacted with each other and the environment.

The National Autistic Society said the exact causes of autism were unknown. In a statement, the society said: "There is evidence to suggest that genetic factors are responsible for some forms of autism. "However, the difficulty of establishing gene involvement is compounded by the interaction of genes and by their interaction with environmental factors. "Various studies over many years have sought to identify candidate genes but so far inconclusively."

In 2006 your lab published a paper in Nature Neuroscience linking a mirror neuron dysfunction to autism. How might reduced mirror neuron activity explain the symptoms of autism?

Reduced mirror neuron activity obviously weakens the ability of these patients to experience immediately and effortlessly what other people are experiencing, thus making social interactions particularly difficult for these patients. Patients with autism have also often motor problems and language problems. It turns out that a deficit in mirror neurons can in principle explain also these other major symptoms. The motor deficits in autism can be easily explained because mirror neurons are just special types of premotor neurons, brain cells essential for planning and selecting actions. It has been also hypothesized that mirror neurons may be important in language evolution and language acquisition.

Thus, a deficit in mirror neurons can in principle account for three major symptoms of autism, the social, motor and language problems.

There is convincing behavioral evidence linking media violence with imitative violence. Mirror neurons provide a plausible neurobiological mechanism that explains why being exposed to media violence leads to imitative violence.

I think there are two key points to keep in mind. The first one is the one we started with: mirror neurons are brain cells specialized for actions. They are obviously critical cells for social interactions but they can’t explain non-social cognition. The second point to keep in mind is that every brain cell and every neural system does not operate in a vacuum. Everything in the brain is interconnected, so that the activity of each cell reflects the dynamic interactions with other brain cells and other neural systems.