The cause of one-third of all autism cases may have been discovered by scientists, a study has shown.

According to a new breakthrough study, up to 33 per cent of autism cases may be caused by low levels of a single protein in the brain.

It is known that people with autism have been found to have lower levels of the protein, called nSR100, but it was uncertain whether this was a symptom, a by-product, or the reason behind the condition.

Now, researchers have found that when they reduce the amount of nSR100 in mice, the animals start to display signs of autistic behaviour.

It suggests that having too little of the protein could be a cause of the condition.

Professor Sabine Cordes, of the Lunenfeld-Tanenbaum Research Institute in Toronto, said: “We previously reported an association between nSR100 protein levels and autism.

“But this time we show that reduced levels of this protein could really be causative – that’s a big deal.

“Just by reducing the nSR100 levels by 50 per cent, we observe hallmarks of autistic behaviour.”

The protein acts as a regulator of a process that creates a number of other proteins, which researchers say are the key building blocks of cells.

The study conclusively suggests that autism is partly the result of incorrectly spliced proteins in brain cells, which could have a number of unexpected effects on behaviour.

“Instead of focusing on individual mutations linked to autism, it’s much more powerful to identify regulatory hubs like nSR100,” said Professor Cordes.

“In the future, if you turned this protein up a little bit in autistic patients, you might be able to improve some of the behavioural deficits.”