The paper is from Leonard et al and it's published in PLoS ONE, so it's open access if you want to take a peek. The authors used a database system in the state of Western Australia which allowed them to find out what happened to all of the babies born between 1984 and 1999 who were still alive as of 2005. There were 400,000 of them.
The records included information on children diagnosed with either an autism spectrum disorder (ASD), intellectual disability aka mental retardation (ID), or both. They decided to only look at singleton births i.e. not twins or triplets.
In total, 1,179 of the kids had a diagnosis of ASD. That's 0.3% or about 1 in 350, much lower than more recent estimates, but these more recent studies used very different methods. Just over 60% of these also had ID, which corresponds well to previous estimates.
There were about 4,500 cases of ID without ASD in the sample, a rate of just over 1%; the great majority of these (90%) had mild-to-moderate ID. They excluded an additional 800 kids with ID associated with a "known biomedical condition" like Down's Syndrome.
So what did they find? Well, a whole bunch, and it's all interesting. Bullet point time.
- Between 1984 to 1999, rates of ID without ASD fell and rates of ASD rose, although there was a curious sudden fall in the rates of ASD without ID just before the end of the study. In 1984, "mild-moderate ID" without autism was by far the most common diagnosis, with 10 times the rate of anything else. By 1999, it was exactly level with ASD+ID, and ASD without ID was close behind. Here's the graph; note the logarithmic scale:
- Boys had a much higher rate of autism than girls, especially when it came to autism without ID. This has been known for a long time.
- Second- and third- born children had a higher rate of ID, and a lower rate of ASD, compared to firstborns.
- Older mothers had children with more autism - both autism with and without ID, but the trend was bigger for autism with ID. But they had less ID. For fathers, the trend was the same and the effect was even bigger. Older parents are more likely to have autistic children but less likely to have kids with ID.
- Richer parents had a strongly reduced liklihood of ID. Rates of ASD with ID were completely flat, but rates of ASD without ID were raised in the richer groups, though it was not linear (the middle groups were highest. - and effect was small.)
Why is this? The simplest explanation would be that there are many children out there for whom it's not easy to determine whether they have ASD or ID. Which diagnosis any such child gets would then depend on cultural and sociological factors - broadly speaking, whether clinicians are willing to give (and parents willing to accept) one or the other.
The authors note that autism has become a less stigmatized condition in Australia recently. Nowdays, they say, a diagnosis of ASD may be preferable to a diagnosis of "just" "plain old" ID, in terms of access to financial support amongst other things. However, it is also harder to get a diagnosis of ASD, as it requires you to go through a more extensive and complex series of assessments.
Clearly some parents will be better able to achieve this than others. In other countries, like South Korea, autism is still one of the most stigmatized conditions of childhood, and we'd expect that there, the trend would be reversed.
The authors also note the theory that autism rates are rising because of some kind of environmental toxin causing brain damage, like mercury or vaccinations. However, as they point out, this would probably cause more of all neurological/behavioural disorders, including ID; at the least it wouldn't reduce the rates of any.
These data clearly show that rates of ID fell almost exactly in parallel with rates of ASD rising, in Western Australia over this 15 year period. What will the vaccine-vexed folks over at Age of Autism make of this study, one wonders?
Leonard H, Glasson E, Nassar N, Whitehouse A, Bebbington A, Bourke J, Jacoby P, Dixon G, Malacova E, Bower C, & Stanley F (2011). Autism and intellectual disability are differentially related to sociodemographic background at birth. PloS one, 6 (3) PMID: 21479223
14 comments:
TL;DR but liked the Age of Autism reference.
I can see how sociological factors can come into it. It is hard and a long haul to get the support and help for an autistic child even in the UK when you are constantly pushing for it...only to find the help is not availble in your area through the NHS.
Certainly interesting findings never the less.
My quess is that ID in general varies enormously amongst social/cultural groups and that autism just is what it is.
For example the genetic disorders in cultures with lot's of inbreeding, as for example with arab cultures, account for for the high incidence of ID and other mental issues.
Afaik autism isn't different there from other cultures making any kind of correlation tenuous at least.
Socrates: At the moment it's looking like they will ignore the study.
It's odd because whenever a study finds that rates of autism have gone up they're usually first on the scene.
I have a question, how is Autism Spectrum Disorder (ASD)linked to Pervasive Development Disorder - Not Otherwise Specified (PDD-NOS), and what is the long term prognosis for this?
My 2.5 yo son has been given both diagnoses in the last few months.
Based on his ability to do jigsaw puzzles, recognize shapes and faces, he has been declared cognitively very advanced. Yet he toe walks, talk incessantly - but incoherently, and has major problems with what's called "sensory integration" issues.
Oh and BTW, my wife and I are older and richer, and both of us work in data intensive fields.
Any answers anyone?
The best treatment for Autism is behavior therapy - either Discrete Trial ( Lovaas ) or Verbal Behavior ( Sundberg and Partington )
In theory, per peer reviewed papers, with 40 hours a week, about 50% fully recover and the other 50% significantly improve
In practise in the field the full recovery rate is about 10% , but the other 90% significantly improve
@pconroy
According to the diagnostic manual of the American Psychiatric Association, currently DSM-IV, PDD-NOS is a subcategory of the category of Pervasive Developmental Disorders. The others are Autistic Disorder, Aspergers Disorder, Rett's Disorder and Childhood Disintegrative Disorder.
Autistic Spectrum Disorder has been used by many researchers and clinicians in preference to the term Pervasive Developmental Disorder because the "distinctions among disorders have been found to be inconsistent over time, variable across sites and often associated with severity, language level or intelligence rather than features of the disorder," according to the American Psychiatric Association, and this will be reflected in DSM-V when it is published, probably next year.
At present PDD-NOS is an autistic spectrum disorder that is indicated "when there is a severe and pervasive impairment in the development of reciprocal social interaction or verbal and nonverbal communication skills, or when stereotyped behaviour, interests and activities are present, but the criteria are not met for a specific Pervasive Developmental Disorder, Schizotypal Personality Disorder or Avoidant Personality Disorder. For example, this category includes 'atypical autism' presentations that do not meet the criteria for Autistic Disorder because of late age of onset, atypical symptomatology, or sub-threshold symptomatology, or all of these." (DSM-V TR, p87, AMA 2000)
The sensory sensitivities you mention are well documented in autistic spectrum disorder but have never been included in the diagnostic criteria. This is set to change with DSM-V. Phoebe Caldwell is one of a growing number of practitioners in the UK who is addressing this issue.
There is no treatment for Autism but patience. Anyone claiming to have a treatment is just comparing behavior to standardized behavior.
As such autism is not treated, the symptoms are treated.
Autism (real autism) is a basic wiring difference of the hemispheres resulting in developmental differences to the norm.
Whilst one can adjust behavior resulting from these differences, one
can't rewire the brain.
This is not a question of neural networks, this a question of the fundamental, permanent construction of the whitematter.
In conclusion:
One can cause behavioral changes by means of forms of CBT, one can't cure autism.
Nowdays, they say, a diagnosis of ASD may be preferable to a diagnosis of "just" "plain old" ID
in terms of access to financial support amongst other things
So does this mean that 'treatment' for ASD and ID are basically the same (if diagnosis boils down to a preference?) Does the preference and the'plain old' suggest ASD is somehow 'trendier' than ID?
However, it is also harder to get a diagnosis of ASD, as it requires you to go through a more extensive and complex series of assessments
So it's harder to diagnose ASD but a diagnosis means more financial and other support...so if you're rich, voila, your kid gets ASD...preferable with a social status is trending up anyway.
I'm not a medical doctor I can see the plausibility of the hypothesis.
If rates of ID fell almost exactly in parallel with rates of ASD rising, and the risk factors are exactly opposite...
It sounds like things stayed the same, but just changed with 'the times'...
At some point— I say around the point where the doctor says 'I don't really know'—
This sounds like a cultural-economic issue not a medical one.
I could have totally misunderstood this, too.
But if this is an accurate assessment, can rich, older women really be considered 'risk factors' for autism?
I really should read the whole paper, but it's 6 am here, and I read the "Biblical Samson Had Autism' post before this and my brain still hurts. (That was awesome).
Forgive my overly long post.
The problem with ID is that the test that determines that is not adequate. It's to coarse and to 'normcentric'
If you construct a test based on the average responses you assume that the average responses are the holy grail. There is no reason to assume that.
As homo sapiens evolves in a civilization (which we do for over 10.000 years now) the brain slowly gets rewired to cope with the demands.
Exceptions to the average may well indicate progress rather then retardation but the test can't differentiate between the 2.
Blandly assuming that if one does certain tasks faster one is better and vice versa is just that, an assumption.
Added to that there's the floating average, plus the totally different results from the same tests across cultures even as close as the american and european one.
In other words: Tests for ID only pick out accurately those who are truly deficient but inaccurately grades those who are just different making the whole argument moot.
Autism spectrum disorders (ASD) often can be reliably detected by age 3. In some cases even earlier than that. Recent studies suggest that kids may eventually be accurately diagnosed by the age of 1 year or even younger. One thing for certain is that if your child shows any of the early warning signs of autism then they should be evaluated by a professional who specializes in autism disorders. Visit my site to learn more about autism signs and symptoms www.americanautismsociety.org
@ Anonymous: "The best treatment for Autism is behavior therapy - either Discrete Trial (Lovaas) or Verbal Behavior (Sundberg and Partington)."
So, like Lovaas, you think it's okay for people to be electrocuted on a regular basis for the 'offence' of not being neurotypical, do you? No wonder you're anonymous. Please try to remember that we're different, not disordered, you Durex in China!
Do you know what Expressive Dysphasia is?
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