LOS ANGELES -- Autism appears to be caused by a reduction in the brain at birth and then extremely rapid development in the first few months of life, researchers in San Diego, California, said.

Researchers, who say they have discovered the 'first glimpse of when autism begins', found that when the brain grows too rapidly in the first few months after a child is born, there is not enough time for accumulation of experiences and emotions that guide and shape 'normal' behaviour.

The first few months is considered an important period for learning and plasticity where the brain is 'experiencing the world' and deciding how to shape and 'construct' itself, said Eric Courchesne, director of the autism research centre at the Paediatric Hospital of San Diego.

The study also found that those with the greatest acceleration of head growth had the most severe autism.

Autism is a developmental disability that typically appears during the first three years of life, resulting from a neurological disorder that affects the functioning of the brain.

Autism and associated behaviours have been estimated to occur in two to six of every 1,000 individuals. Males are four times more likely to have autism than females.

The study, still in its preliminary stages, could lead to a system of measuring the brains of newborns and controlling the growth of those seeming likely to develop autism, Dr Courchesne said. -- AFP