Scientists have succeeded in identifying signs of autism in babies who were just a few months old.

Autism, also known as autism spectrum disorder (ASD), is a biological disorder of the brain that impairs communication and social skills. Signs can include an absence of eye contact, apparent aloofness, avoidance of physical contact even with family, difficulty dealing with interruptions to routine and a lack of interest in other children and what they are doing.

While most children are diagnosed by the age of three, some may be older. However until now, it was generally acknowledged that symptoms are difficult to detect in the first six months of life.

US scientists decided to investigate this further. They looked at two groups of infants. One of the groups was at low risk of developing autism, while the other was at high risk. A child is considered to be at high risk if they have a sibling with the condition. In fact, this increases the risk 20-fold.

Children are considered at low risk if they have no first, second or third-degree relatives with the condition.

The scientists followed the progress of the infants by using eye-tracking technology, which measured the way the babies looked at and responded to social cues.

Before babies can crawl or walk, they explore the world through sight - by looking at people and objects. This is a necessary part of their development and is important for brain growth.

"By following these babies from birth, and intensively within the first six months, we were able to collect large amounts of data long before overt symptoms (of autism) are typically seen," explained the study's lead author, Dr Warren Jones, of the Marcus Autism Center at Emory University in Atlanta.

The scientists assessed all of the children and autism, when present, was confirmed at the age of three. They then analysed data from the children's early months to see if they could find differences between those who went on to be diagnosed with autism and those who did not.

They found that those who were diagnosed with autism displayed a declining attention to the eyes of other people from the age of just two months.

"We found a steady decline in attention to other people's eyes, from two until 24 months, in infants later diagnosed with autism. First, these results reveal that there are measurable and identifiable differences present already before six months. And second, we observed declining eye fixation over time, rather than an outright absence," explained co-investigator, Dr Ami Klin.

She emphasised that the fact that these differences were apparent even within the first six months of life has profound implications. However, she explained that differences in eye contact would not be visible to the naked eye.

They require special eye-tracking technology and repeated measurements of development over the course of several months.

"To be sure, parents should not expect that this is something they could see without the aid of technology and they shouldn't be concerned if an infant doesn't happen to look at their eyes at every moment. We used very specialised technology to measure developmental differences, accruing over time, in the way that infants watched very specific scenes of social interaction," Dr Jones explained.

The researchers said that these findings are important because if infants were identified as having autism at such a young age, interventions could be introduced at a much earlier stage.

This could be especially important for children with more severe forms of autism. The study found that those whose levels of eye contact decreased the fastest over time, had more severe forms of autism later on.

"The genetics of autism have proven to be quite complex. Many hundreds of genes are likely to be involved, with each one playing a role in just a small fraction of cases, and contributing to risk in different ways in different individuals.

"The current results reveal one way in which that genetic diversity may be converted into disability very early in life. Our next step will be to expand these studies with more children, and to combine our eye-tracking measures with measures of gene expression and brain growth," Dr Jones added.

Details of these findings are published in the journal, Nature.