Contrary to reports that the rates of autism spectrum disorder are on the rise, researchers at the University of Queensland found no evidence of an increase of the condition in the past 20 years.
Norman Swan: Autism Spectrum Disorder describes children and adults who have a range of difficulties with communicating, socialising and can also have quite obsessional interests and repetitive behaviours.
Some advocates for people with Autism Spectrum Disorder have claimed that it's becoming more common and have blamed environmental influences: most controversially (and wrongly) the mumps, measles and rubella vaccine.
Amanda Baxter is at the Queensland Centre for Mental Health Research at the University of Queensland. Amanda and her colleagues have just published a large study suggesting there's no rise at all.
Amanda Baxter: What we did was review all of the research over the past 30 years from across the world. Taking into account different study methods we were able to estimate the prevalence of autism spectrum disorder across the lifespan across the world, and from that we were able to calculate the disease burden caused by the disorder.
Norman Swan: And when you say prevalence, this is the number of people living with this problem rather than the number of new diagnoses each year.
Amanda Baxter: That's exactly right.
Norman Swan: And what did you find?
Amanda Baxter: So what we found was that the way in which studies were conducted did have a big impact on the prevalence that was reported, and once we got rid of that we found that prevalence across the lifespan was about one in 132 people. And what we were able to highlight was that because their condition starts so early in life…and it's a chronic disease so it continues right across life…a lot of those people who currently have the disorder are adults, and so approximately 52 million people in the world who have an autism spectrum disorder have actually transitioned into adulthood.
Norman Swan: So in other words while people think of this as a childhood problem, children grow up. And because there are more adults in the world than children, there are more adults with autism spectrum disorder than children.
Amanda Baxter: That's exactly right. It was also interesting in that we did not just find it in the westernised societies, we found that the rates were relatively steady in populations right around the world. And we also found that rates were relatively stable over time. So the prevalence we found for 2010, which was about 0.8% of the population, was very similar to what we found for 1990.
Norman Swan: So what do you take from that, that it's a genetic problem rather than environmental or what?
Amanda Baxter: Yes, that's exactly right. It is very much a biological disorder with a very strong genetic basis. That does tell us that it's a disorder that has been around for a very long time and will continue to be around.
Norman Swan: Because the other problem with it is…but you imply that you sorted that out…is that there are different ways of diagnosing this. So if you use the World Health Organisation criteria, the diagnostic rate is probably lower than if you use the American DSM.
Amanda Baxter: That is certainly a challenge at the clinical level. What would be extremely useful is to use a very consistent screening tool and use consistent diagnostic criteria. In terms of the difference between the World Health Organisation criteria and the DSM is that I found the prevalence was very similar.
Norman Swan: So in terms of global burden, how does autism spectrum disorder compare to other problems?
Amanda Baxter: It came in as quite a significant problem, certainly in children under the age of five it was among the top 20 causes of disability in the world. To give you a figure, there was 7.7 million person years of healthy life lost in 2010.
Norman Swan: I suppose it wouldn't be a surprise to a parent of a child with what used to be called Asperger's syndrome because they know the disability their child suffers.
Amanda Baxter: Exactly right.
Norman Swan: And presumably it's high because it's lifelong and therefore the disability starts early and therefore the detriment is potentially huge.
Amanda Baxter: That's right. We are probably not going to be able to prevent it but what we can do is identify it at a young age and get those people into treatment at an early age in order to minimise the burden on the individuals and their families as well as the community down the track as people transition into adulthood.
Norman Swan: Amanda Baxter is at the Queensland Centre for Mental Health Research at the University of Queensland.
Editor's note: The claim "we found that prevalence across the lifespan was about one in 132 people" is contrary to substantial evidence and expert opinion. The number of children diagnosed with ASD in Australia and in USA has risen to well above 1 in 132 ... and there are no credible reports identifying over diagnosis of ASD in these settings. The prestigious science journal, Nature, recognises increasing ASD diagnosis rates and says awareness may only be part of the reason for the increase.