Getting a diagnosis for autism is not easy, with many children having to wait to see specially trained doctors and specialists who spend hours observing the child’s behaviour before rendering a verdict. But U.S. doctors are working on an experimental blood test they believe might help detect the disorder – even before symptoms begin.

Dr. Isaac Kohane, a pediatric endocrinologist at the Boston children's hospital who is the lead researcher behind the effort, says the blood test would be based on looking at gene signatures.

He says a number of gene mutations -- such as lost or extra copies of a gene or genes -- have already been discovered and appear to be linked to autism. But these known mutations account for fewer than 20 per cent of autism cases.

What his team looks for instead is a 55-gene signature, meaning a group of genes whose combined expression pattern indicates the possibility of autism.

“We found in comparing kids with autism and without autism that the pattern of genes that are on and off are a very good predictor of which children have or will go onto have autism,” he told CTV’s Canada AM Thursday from Boston.

Kohane’s team recently published a study in the journal PLOS ONE, in which they describe how they analyzed blood samples from 66 boys with autism spectrum disorder and compared them with 33 age-matched boys without the disorder.

They flagged 489 genes as having distinct expression patterns in the autism group, then narrowed them down to a group of 55 genes. They say the pattern of those genes correctly identified or ruled out autism in 76 per cent of samples.

They then ran the test on a second group of 104 boys and girls between the ages of 3 and 12 with autism and compared them with 82 kids without. The test was 68 per cent accurate in spotting the kids with autism -- 73 per cent accurate in the boys and 64 per cent in the girls.

Kohane says there is a lot more work to do to refine the test. But he says if a blood test could be developed, it would be a great tool that could provide guidance to doctors when there is a suspicion of autism.

“In the U.S., the average age of autism evaluation is age five, which is unfortunate because if you can diagnose children earlier, for example at age two, you could actually treat them -- even without new pharmacological therapies – in ways that improve their outcomes, such as their IQ,” Kohane said.

Kohane’s test has already been licensed to a company, SynapDx, for commercial development. However, it’s not going to become available until it can be shown to highly accurate, Kohane says.

He adds that there are now experiments being conducted in several pediatric centres across the country to evaluate the test.

Kohane points out that the blood test would not be intended as a screening tool for the general public, but to guide doctors when there is a suspicion of autism -- for example, in a child with a speech delay.

“We wouldn’t have to wait in line for these special clinics. We would be able to say ‘These kids are at risk,’ and then put them at the head of the queue and treat them early,” Kohane explained.

What is remarkable about this test, says Kohane, is that it suggests there isn’t just one kind of autism, but a whole spectrum.

“What this test is showing is -- as we were beginning to suspect from other studies -- is that there are many different causes of autism, just as there are different causes of heart disease for example,” he said.

He notes that in his study, some of the genes that switched on and off are considered classical neurological genes, while some are more like immunological genes.

Previous studies of brain tissue from patients with autism have found significant activation of immune cells in the brains of some people with autism. Kohane speculates that brain development might be impaired by abnormal immune responses to infections or other stressors during infancy or in the womb.

Dr. Daniel Geschwind, a professor of neurology and psychiatry at the University of California, who was not involved in the study, tells The Boston Globe that while he welcomes research into a blood test to identify those at risk of autism, there is still a long way to go in refining such a test to eliminate false positives.

He suggests while it’s possible the test can detect “a general signal” in families with autism, it could also mistakenly flag siblings of those with the disorder.