Does John Elder Robison Understand Autism Prevalence?

John Elder Robison is a "bestselling author, autism advocate, and founder and owner of J E Robison Service Company of Springfield, Massachusetts" and serves on the the scientific advisory board of Autism Speaks.

Mr Robison is in a position to help decide what research Autism Speaks should fund, so I would expect him to be quite knowledgeable when it comes to the science of autism. Yet from some of his recent comments, I am not sure that he grasps the science behind one of the fundamental questions about autism - is autism increasing?

Below is something that Mr. Robison recently wrote about the increase in autism as part of a larger conversation. I am not going to address the main points of the discussion because Jonathan already did a good job of that at Autism's Gadfly. Instead, I want to focus on his statements about the apparent increase in the rates of autism -

The 600% thing may be misleading, but it's still real. Is some of it caused by more inclusive standards in the new DSM? Sure. Is some caused by much greater public awareness? Sure. Is some caused by increases in certain kinds of autism . . . probably. There have not been any studies to clarify this point because there is no data on the prevalence of certain kinds of autism in years past - there's only data on the whole spectrum. It's very hard to explain the reason for the increase and no one has figured out a way to determine if certain conditions like childhood disintegrative disorder are increasing, or just more visible. The same can be said for Asperger's.

The 600% refers to the apparent increase in autism rates over the past decade or so. Now, I have to give Mr. Robison credit for actually admitting that "certain types of autism" are "probably" increasing. But all of the credit goes bye-bye when he says (presumably with a straight face), that increases in conditions like childhood disintegrative disorder might be responsible for part of the increase and that there is no data on the breakdown of the spectrum.

For those of you who don't know, childhood disintegrative disorder (CDD) is a very rare condition that is one of the five conditions that together make up the pervasive developmental disorders - more commonly known as the autism spectrum.  And while it is true that children with CDD do look a lot like children with autism, there are some very significant differences.  Children with CDD have an extended period of "normal" development (at least 2 but no longer than 10 years) before undergoing a very significant (and most times very rapid) regression where previously acquired social, communication, and motor skills are lost.  After the regression, these children do show the same behaviors as other forms of autism but, unlike other forms of autism, once skills are lost, they are typically never regained.

To put it bluntly, when your child goes from being a bright talkative five year old to being a child with an intellectual disabilty who no longer talks, looses motor skills, and no longer has bladder control and stays that way for the rest of their life, that would be CDD.

CDD can make even lower functioning autism look good by comparison.

The strange thing is that it isn't like we have no idea how how (un)common CDD is. All the way back in 2002, there was a review article published that cited prevalence estimates from 1966 onward and came up with a figure of about 1.7 per 100,000 for CDD.  Compare that to the recent CDC figure of about 910 per 100,000 for all types of autism.

Even if CDD has seen the same massive increases that other forms of autism did over the past decade, we are still only talking about 10 per 100,000 compared to 910 per 100,000.  But I have not been able to find any published work that even suggests that the rate of CDD could have increased this much and, as recently as 2009, the 1.7 per 100,000 figure is still being used.

So, in other words, if you ignore all of the data that has been published on the subject and make some huge leaps of faith, you could possibly conclude that about 1% of all current autism cases are CDD.  However, a much more realistic scenario is that CDD hasn't increased so drastically and makes up less than 0.5% of all autism cases.

In either case, it is highly unlikely that an increase in CDD is a major (or even minor) factor in the 600% increase in autism.

Which leads into the second problem with what Mr. Robison said - that we don't have a clear picture of what types of autism are increasing.  If you even do a quick search, you can turn up several places where breakdowns have been done. Take for example this study from 2009 that clearly gives a breakdown between the types of autism -

This article reviews the results of 43 studies published since 1966 that provided estimates for the prevalence of pervasive developmental disorders (PDDs), including autistic disorder, Asperger disorder, PDD not otherwise specified, and childhood disintegrative disorder. The prevalence of autistic disorder has increased in recent surveys and current estimates of prevalence are around 20/10,000, whereas the prevalence for PDD not otherwise specified is around 30/10,000 in recent surveys. Prevalence of Asperger disorder is much lower than that for autistic disorder and childhood disintegrative disorder is a very rare disorder with a prevalence of about 2/100,000. Combined all together, recent studies that have examined the whole spectrum of PDDs have consistently provided estimates in the 60-70/10,000 range, making PDD one of the most frequent childhood neurodevelopmental disorders.

Notice how the two types of autism that Mr. Robison called out - CDD and Asperger's - are both listed as being rare relative to a overall rate of 60-70 per 10,000.  The bulk of the cases of autism in this review are either PDD-NOS or classic autism.

The current rate for the entire spectrum is about 90 per 10,000 and, as the CDC said in its most recent report, the increase from the earlier 60 per 10,000 isn't all in the conditions like Aspergers.  As a matter of fact, the increases are somewhat spread out but the classic autism category might show a greater increases than the other conditions -

The widening of diagnostic criteria over time to include persons who are more mildly affected has been suggested frequently as a factor influencing increases in ASD prevalence. (snip) However, in this analysis, a clear shift was not identified from 2002 to 2006 in the use of the more broadly defined ASD diagnoses. In fact, for several sites, increases were recorded in the use by community professionals of the autism diagnosis rather than the other ASD diagnoses. Another indicator of identifying children on the more mild end of the spectrum would be a differential increase in prevalence among children with borderline or average to above-average cognitive functioning. Although the overall pattern among these higher cognitive functioning groups indicated substantial increases in ASD prevalence, increases also were observed among children with cognitive impairment. Increases varied across sites, and a clear pattern did not emerge that would permit attributing the majority of the increase in ASD prevalence to the use of the broader ASD spectrum.

So for Mr. Robison to suggest that any significant part of the increase in autism is due to CDD or that we have absolutely no idea what type of autism is increasing is disingenuous at best and intellectually dishonest at worst.  What is he doing serving on the scientific committee of Autism Speaks if he can't even get the basic facts right?