Tuesday, September 28, 2010

Jabberwocky of the Day : Faking Autism

I know that not everyone understands autism.  I understand that some people need are going to need extra guidance to understand exactly what it means to have autism. And my family has, like every other autism family out there, encountered some degree of hostility from the public at large when we take our children out in public. I fully expect to have to keep explaining my children's disability to strangers for decades to come.

I get all that and it is par for the course for an autism parent.  What I have a hard time understanding are people who are utterly ignorant of what autism is and yet seem to feel the need to share their ignorance with the world.

Take for example a comment that I saw earlier today on a story about Sharron Angle. Some person calling themselves "behyndblueeyes" took the time to write something so absurd that I can't even begin to describe it, you have to read it for yourself.

I can't seem to find a way to get a direct link to the comment, but the time on the comment is 9/27/2010 2:04:17 PM so if you scroll through the comments, you should be able to find it.

Here is the text of the comment -
It is my understanding that some parents of autistic children are exploiting the system. They coach their children to behave as mentally challenged when they visit a doctor. Many of whose children have no such handicap, however these parents will seek out a doctor that will make a claim of such a handicap. As a result, parents of these so called "autistic children" receive an extra $500 monthly payment given to them by the taxpayer to assist in their child's needs. Of course, that isn't how it works. The parents simply have another $500 a month coming from the taxpayers to squander on their own pleasures.
So yes, there are grounds to question the legitimacy of autism claims.
Anyone with an adolescent child can make these claims, coach them to appear abnormal and silent in the presence of their doctor to steal from the taxpayers. I would suggest that all claims of autism requires an MRI scan to help determine whether a child truly has this condition.
I can only marvel at the sheer ignorance of this person and the lack of facts in their comment.

I don't know if you could teach a teenager to "act autistic" or not, but I can't believe for a second that any qualified doctor would be so easily fooled.  I am not saying that it could never happen, but the kid would have to be a tremendous actor to pull it off and, even then, there are many involuntary tells that would give them away (hint - watch the kids eyes to see what they look at).  Plus that ignores the fact that there are psychological tests like the ADOS that are designed to help diagnosis autism.  It isn't just a matter of having your kid not talk and flap their arms in the doctor's office, there would be so much more to it than that.

I don't know of any government program that gives parents $500 a month for having a child with autism.  Maybe there are such programs in other states, but I have never heard of one.

And then, to suggest that an MRI be performed to somehow validate the claim of autism.  I have to wonder what they think an MRI will show.  Apparently they have not taken the time to even look up basic facts about autism.  If they had, they would have know that there are no quantitative tests for diagnosing autism - you can't tell from an MRI, blood, or other physical test that someone has autism.

I would like to think that this sort of ignorance is rare, but unfortunately it is not.  If you look at some of the other comments on this story, you will be treated to other opinions that are just as bad as this.

I think it is important to remember that addressing this sort of ignorance needs to be one of the main goals of the autism community.  It is too easy to look inward and argue amongst ourselves about vaccines, causation,  difference vs disability, functioning level, or other such minutia and forget that the rest of the world is rather ignorant about autism.

Sunday, September 26, 2010

Aspie Bigotry at Autism Speaks Blog

Earlier this month, an opinion post appeared on the "Autism Speaks Official Blog" that talked about the differences between Asperger's Syndrome and Autism. The opinion post was written by one Hannah Fjeldsted, a college senior who has Asperger Syndrome. The entire post was about how the Ms. Fjeldsted feels that grouping people with Asperger's (aka "aspies") in people with autism is somehow an insult and degrading to them.

I guess the irony of being an advocate for the acceptance of people with Asperger's while at the same time bashing their less fortunate peers is somehow lost on her.

With this rant, Ms. Fjeldsted joins the growing ranks of aspie bigots who think that they are better than the rest of the people on the spectrum and should not be lumped in with "them". Like other bigots before her, Ms. Fjeldsted is laboring under the false impression that Asperger's Syndrome is currently a separate condition from the other types of autism and that the upcoming DSM V is going to force people with Asperger's to be lumped in with the rest of the spectrum.

Nothing could be further from the truth.

Asperger's is already, by definition, a form of autism. It is included in the current DSM IV under the pervasive developmental disorder category along with autism, pdd-nos, Rett Syndrome, and childhood disintegrative disorder. It is this group of conditions that make up what is typically called the "autism spectrum".

So sorry Ms. Fjeldsted, if you have a diagnosis of Asperger's you are already one of "them".

Factual problems aside, the rant is quite entertaining in its own way, with some breathtaking statement of intolerance such as -
As someone with Asperger’s, I am strongly opposed to this proposal and I firmly believe that autism and Asperger’s should continue to be classified separately. This proposal will do more harm than good because it will further perpetuate stereotypes and misunderstandings about Asperger’s, it will serve as an insult and a mockery to those who are severely affected by Asperger’s, it will cause further confusion and ambiguity in diagnostics, and it will attack the identity in which many Aspies, like me, take pride.
First of all, many Aspies already suffer enough from the negative stigma and stereotypes society holds against them. To call Asperger’s “high-functioning autism” or “a form of autism” will only contribute to this stigma. The label of Asperger’s at least gives observers the impression of intelligence and ability. But, when most people think of “autism,” they think of someone who should be institutionalized and cannot live independently. Therefore, if people with Asperger’s are merged under the autistic group, brilliantly gifted and capable individuals could be unfairly stereotyped as incapable and unprofitable.
You really have to read the whole piece to get the complete picture, these snippets cannot do it justice. The overall tone is elitist and the whole thing is one big insult and stereotype aimed squarely at people who suffer most from autism.

I am not the only one who found this post insulting and, in what is probably a record for the Autism Speaks blog, there are 74 comments on the post, the overwhelming majority of them being highly critical.

I am not sure what I find to be more troubling here - the fact that there are so many aspie bigots like Ms. Fjeldsted out there or that Autism Speaks gave one of them a platform for their bigotry.

To its discredit, Autism Speaks did respond to the angry comments with a comment of their own -
It is noted that these words are the opinion of the author, not necessarily representative of Autism Speaks. We aim to present a variety of opinions from members of our community. The author’s viewpoint is simply that – her opinions.
So their response was a very lame "we didn't say she did". While I can understand that people have a variety of opinions, Autism Speaks should not be in the business of giving a platform to an opinion that is insulting and demeaning to the group that they are supposed to be serving. Autism Speaks needs to grow a pair and take a stand against stupidity like this. Bigotry against people who suffer from autism is not a valid viewpoint.

I wish I could say that opinions like Ms. Fjeldsted's are rare, but they seem to be becoming increasingly common. I think the neurodiversity movement is in large part to blame for this with their absurd notion of autism being just a difference. It is one thing to accept people as people, limitations at all, but completely another to romanticize a medical condition like autism. Autism is a very serious development disorder that causes major problems for those affected. It is a medical condition that requires treatment and a cure, not some civil rights movement.

So Hannah Fjeldsted, if you want to take pride in being an "aspie" and want think of it as you "identity" and don't want to be lumped in with those others, you know, the ones that belong in institutions, here is my suggestion.

Get the hell off the spectrum and go find some other group of disabled people to insult.  People with autism and their caretakers have enough to worry about without having to deal with your bigotry.

Saturday, September 25, 2010

The Politics of Ignorance

Sharron Angle, the Republican candidate for United States Senate in Nevada, was caught on video trash talking insurance coverage for autism treatments. You can see listen to her remarks on YouTube yourself but what she said was -
"Take off the mandates for coverage in the state of Nevada and all over the United States. But here you know what I’m talking about. You’re paying for things you don’t even need. They just passed the latest one, is everything that they want to throw at us now is covered under 'autism'"
If you watch at the video, you can see her make air quotes around the word autism.


I don't like to talk about politics because subject is typically a land mine in this country. If you think people in the autism community are touchy, try and have a rational political discussion with someone.  But, I didn't think I could let these statements without comment.

While most the of the criticisms about her remarks have centered on the use of air quotes around the word autism, I think that misses the larger issue.  Sure, if you think the term autism belongs in air quotes and parents are just lining up to get their kids an autism diagnosis because of the perks, then you are just ignorant of what autism is. But parents whose children have autism have to deal with that type of ignorance all the time, so it isn't a surprise that a politician would say it.

No, what I find more troublesome is the opposition to insurance coverage of autism treatments. The law that this women is opposing is not some radical plan that covers off the wall treatments for the autism, it is a law that forces insurance companies to pay for the basics -
Requires private health insurance companies to provide coverage for the screening, diagnosis and treatment of autism spectrum disorder.· Coverage of treatments will be provided when prescribed for an individual diagnosed with an Autism Spectrum Disorder by a licensed physician or a licensed psychologist who determines the care to be medically necessary.· Coverage will be provided to individuals under the age of 18, or through the age of 21 if the individual is enrolled in high school. Coverage under this bill is subject to a maximum benefit of $36,000 annually for Applied Behavior Analysis (ABA) therapy.·The bill includes coverage of the following treatments when written into a treatment plan: Habilitative or rehabilitative care, Prescription drugs, Psychiatric care, Psychological care, Therapeutic care (Speech and Language Therapy, Occupational Therapy, Physical Therapy), and Applied Behavior Analysis (ABA), and behavioral therapies.· The bill defines "behavioral therapy" as "any interactive therapy derived from evidence-based research, including, without limitation, discrete trial training, early intensive behavioral intervention, intensive intervention programs, pivotal response training and verbal behavior"
I find Sharron Angle's opposition to this law very troubling because by opposing insurance companies paying for medically necessary autism treatments she is effectively opposing using these treatments for autism.

Let me explain.

All of the services covered by this law are provided by trained professionals and the services of these professionals do not come cheap. For example, assume that you have a child receiving speech therapy one time a week from a trained speech therapist, that would run you about $5,000 a year. Add in OT and you have another $5,000 a year. When you add in behavioral therapy such as ABA those costs go up substantially, at least another $15,000.

Put that all together and you are talking at least $25,000 a year per child and most of the time much more. 

Now consider that there are many families, like mine, where there is more than one child with autism. If I had to pay for all of the core treatments out of pocket, I would be paying at a minimum $60,000 a year.   If I could pay for these services out of pocket I would, but that is just not feasible.  My family relies on my private health insurance as well as the programs from the state to pay for these services.

Don't get me wrong, I am not looking for a handout nor do I feel that I am somehow entitled to these services. But services like these are the best chance that my children have at being able to live productive, independent lives.  It is in society's best interesting to have as many of the children like mine as possible learn to live independently.  The alternative is even more expensive.

So when Sharron Angle is advocating against insurance paying for the basic autism treatments, she is basically saying that she is against treated autism because very few families cannot afford these services on their own. And that means that Sharron Angle is against giving your child who happens to struggle with autism the help that they are going to need if they are going to overcome their autism.  So, let me but this bluntly.  If you have a child with autism and vote for Sharron Angle you are voting against your child's future.

The country doesn't need any more elected officials who are badly ignorant of the realities of "autism".

Friday, September 24, 2010

Genetic Mutations in Autism - Cause or Effect?

Whenever you read anything about autism you will quickly run into the belief that autism is mostly "genetic".  The idea is that something, somewhere is not quite right with a person's genetic code and it is this difference that leads to the symptoms that make up what we call autism.  This belief is largely based on twin studies that show that identical twins are more likely to both have autism than non-identical twins and based on findings that children whose siblings or parents have autism are more likely to have autism themselves.

Based on this theory, millions upon millions of dollars have been spent looking for the genetic "causes" of autism.  But even though a large amount of time and money has been spent looking, there has been very little success.  Many studies have found genetic mutations that appear in a very small number of cases - typically much less than 1 percent. But whenever other researchers look for the these mutations in other groups, they almost always come up empty.

What this leaves us with is a large number of genes that might be involved in some way shape or form with a very small number of cases.  If we add up all of these cases - and make the rather large assumption that they don't overlap - we might reach a total of 10 to 20 percent of all autism cases.  That means we would have 10 to 20 percent of cases made that might be caused by twenty to thirty distinct mutations.  And that is just talking about the mutations that involve a sizable population (even if it is under 1 percent of the whole).  Under this sort of model, the other cases would also have mutations but they could almost be unique to the individual case.

At the end of the day, we would be likely talking about a hundred or so unique mutations that could play a role in causing autism.

To make matters worse, even when we can find these mutations, rarely do we have any real understanding of how these mutations could lead to something like autism.  And then even in the extremely rare cases when we do understand what these mutations might be doing, we have no clue of what can be done to fix the problem.

When you consider the failure of science to identify the genetic underpinnings of autism - or even to find any underlying mechanism that could cause autism - you have to ask yourself whether the mostly genetic model of autism is right.  Is autism really caused by a huge number of almost individualized mutations or is something else going on?

I have a idea that I have been thinking about for a while now.  What if all of these rare genetic mutations that are found in autism are not the cause of autism but rather a side effect of autism or collateral damage from whatever process caused the autism?

I know that this is pure conjecture on my part, so take it for what it is worth.  But consider the following.

First, a large number of the genetic mutations that have been found to be associated with autism are de novo, meaning that the mutations are seen in the children but not in their parents.  While this does not mean that autism isn't genetic, it does put a rather large dent in the idea that autism runs in families. It also makes you wonder what is going on with twin studies, but I will get to that point in a minute.

Second, when you look at current estimates on how often identical twins both have autism, you will see that some of the earlier studies were overly optimistic.  More recent research is showing that identical twins will only both have autism 80 to 90 percent of the time and, even when they do both have autism, one can be more severe than the other.  While it is true that identical twins will start to differ over time on a genetic level, before the age of three there should not be any major genetic differences.  As a result, if autism were solely based on genetics this number would be a lot close to  100 percent and the severity would almost always be the same.

Third, when you look at fraternal twins, they are much more likely than typical siblings to both have autism.  Recent research has shown that male male fraternal twins have up to a 40 percent chance of both having autism while other types of siblings have only an 2 to 8 percent chance.

For those of you who don't understand the details of the different types of twinning, the simple way of thinking about it is as follows.  Identical twins alway start out as one fertilized egg - one organism - that splits into two separate organisms sometimes in the first nine days after fertilization.  Depending on how late the identical twins split they will share either a placenta, amniotic sac, or both.  If they split early enough then they will share nothing.  Fraternal twins are two fertilized eggs and are no more alike than other siblings would be.

The thing that all twins have in common is that they share, to some degree, the prenatal environment and tend to have very similar post-natal environments as well (just take my word for it).  Identical twins tend to share more of the prenatal environment while fraternal twins share less.  Normal siblings, of course, do not share any of the prenatal environment.

This leads me to my last, and mostly anecdotal, set of reasons why I think that the small mutations are an effect of autism rather than a cause.  For those of you who haven't been reading here for a while, two of my daughters with autism are identical twins.  While they are both about the same severity and share the same core deficiencies (primarily communications), it is striking how different their autism looks.  For example, Twin A has great imaginative play skills which Twin B lacks but Twin B is much more in tune socially with other children and adults than Twin A.

It is easy to tell when something about them is being driven by genetics because they are almost identical.  Even when you have something that you wouldn't think is genetic, they still stay very close to each other.  For example, they have had different eating habits for several years now but have stayed the same height and almost the same weight as each other for five years now.  This year is the first time that they differed by more than an ounce or two but they are still the same height.

What I find striking is how different their autism looks and the different areas that they have problems with. For example, Twin A does not like noise and gets upset when there is too much background noise.  But Twin B wants to have constant background noise and gets upset when there isn't enough.  It is almost like their autistic behaviors are more like personality traits rather than something predetermined by genetics.

More important, however, is the genetics of these two young girls.  Earlier this year we have a microarray test done on both of them to look for genetic mutations that could cause their autism.  We know that they are in fact identical twins because we had genetic testing done that confirmed this.  So imagine our surprise when the tests came back with different, non-overlapping mutations.

Twin A has two smaller copy number mutations (copy loss) located on two chromosomes while Twin B has one larger copy number mutation (copy loss) on a different chromosome.  All three mutations have appeared in various studies that looked for rare mutations in autism, although none of them was a major finding.

Let me say that again - identical twins who have different genetic mutations.  Clearly these mutations cannot have been inherited.

Just a few other, more technical points.  The twins were dichorionic-diamniotic twins which is just a fancy way of saying that they split relatively early (1 to 3 days) and had separate placentas and separate amniotic sacs.  In other words, they shared about the same amount of their prenatal environment as fraternal twins do.

Furthermore, their mutations do not show any evidence of being in only some of their cells not more others because the test we used would have picked up on that (ok, not strictly true, but true enough for this discussion).  This means that the mutations had to have happened very near to conception when there were very few cells so that the mutation would effect all of their cells.

So when you put these facts together you are left with the conclusion that these mutations happened at some point after they split off from each other (1 to 3 days) but early enough that whatever caused the mutations hit them both and could change most of their cells  (first 9 or so days).  I have no idea what that event was but I would guess that something strong enough to cause permanent genetic damage would also be able to cause autism.

So what do you think, do these mutations cause autism or does whatever causes autism also cause these mutations as a side effect?

Wednesday, September 22, 2010

Folic Acid Increases the Risk of Autism aka the Dangers of Bad Data

As I talked about last time, another study on thimerosal was released last week.  Like some of the studies before it, this one found that not only was thimerosal not involved in causing autism but also that a higher exposure actually lowered the the odds of having autism.  Or in other words, being injected with a higher level of mercury actually greatly decreased your chances of having autism.

If that result seems a bit strange to you, you are not alone.  I don't think that many people would claim that this is actually a valid finding (although there are some) and the researchers acknowledged as much when they said that they "are not aware of a biological mechanism that would lead to this result."  Although, to be slightly glib, it would be one of the great ironies in recent history if thimerosal actually did actually protect against autism.

But still, the result reached statistical significance which means that it is unlikely to have happened by chance, and this isn't some fly by night paper were the statistics were in doubt.  The data in this paper was the result of a seven year effort and the published paper and supplemental material reaches almost 400 pages.

I think the answer to the puzzle is pretty obvious here and I am going to use another significant finding from the study to illustrate the point.  Buried on page 164 of Volume I of the supplemental material is the following statement -

"Use of prenatal vitamins containing folic acid was associated with a higher odds ratio of ASD"

This is also a statistically significant relationship.  If you look on page 169 of the volume, you will see that, if the mother took prenatal vitamins while pregnant, her children were more than twice as likely to have autism.  This result is based on the data that 96% of the mothers of children who have autism took folic acid while only 91% of the mothers of "typical" children did.  When you put these numbers into the models with the rest of the data - the same models used to determine the main no relationship result - out pops this strange relationship.

For those of you who don't know, folic acid is essential to many bodily functions, is used to help synthesize and repair DNA, and helps determine which parts of the generic material is active.  Pregnant women have been taking folic acid during pregnancy since at least 1993 because it can mostly prevent neural tube defects such as spina bifida.

Here we have yet another improbable result from this study.  So, what could be going on?

When you consider the facts that folic acid plays a role in maintaining and repairing genetic code and that autism seems to littered with many rare genetic mutations, it might be possible that taking too much folic acid during pregnancy could increase the chances of a child having autism.  However, even though the timing (1993 onwards) might agree with rising autism rates and there might be some kind-of plausible mechanism for the relationship, I don't think that this is likely.

Which leads to another possibility.  I am sure that most of you have heard the oft-repeated phrase about how correlation does not imply causation - this would be a classic example of it.  It is possible that folic acid use is highly related to another factor and it is this other factor that is causing autism.  If I had to guess, folic acid use during pregnancy could be be correlated with affluence.  Meaning that mothers who are more well-off are more likely to wait until later in life to have children and are more likely to do the "right" things during pregnancy - such as take folic acid.  But it is equally likely that this relationship could be flipped and affluence, which has been linked elsewhere to a higher risk of autism, is the dependant factor and it folic acid use that is the causative factor.  That is the problem with these sorts of relatinships, you are never quite sure what is a cause and what is simply along for the ride.

Another explanation would be that the association would happen by simple dumb luck.  Even with all of the robust methodologies and fancy statistics that researchers use, it is still possible for a significant result to appear that is due to simple random chance.  This is why it is very important that all scientific findings be replicated by other researchers using a different set of data.  The fact that thimerosal is actually protective has been suggested by other studies but I am not aware of any others finding a relationship with folic acid use.

Regardless, I think the most likely explanation for what is going on is the simplest - there is a problem with the study's data.  I would have to say that a problem with the underlying data is one of the most overlooked and under-considered problems out there.  If the data that the analysis and conclusions of the study are based on is biased or does not properly represent what you trying to study, everything that the data is based on is flawed.

Since this study found that a higher exposure to thimerosal decreases the chance of autism and that taking folic acid during pregnancy raises the chance of autism, I think it is safe to say that something is not quite right with the data in this study.

As the saying goes - garbage in, garbage out.

Sunday, September 19, 2010

Yet Another Thimerosal Study

Earlier this week, yet another study was published that failed to find a link between thimerosal in vaccines and autism.  This long awaited study was commissioned by the CDC and is the first serious look at the relationship between thimerosal and autism in US based populations since the controversial Verstraeten study in 2003.

The study looked at 256 children with autism and matched them against 762 typical children and found that the amount of thimerosal that they were exposed to had no relationship to their chances of having autism.  Or in simpler terms, more mercury did not mean more autism.  And actually, some of the analyses showed that having a higher exposure to thimerosal actually decreased the chances of having autism.

Yes, you read that correctly.  The study found that more mercury meant less autism.

I was planning on writing a serious review of the pros and cons of this study because I think that this is an important one.  But the more that I dug into the study, the less sense that it made to me.  Sure, the study is well designed and appears to have been carried out meticulously.  But how the data was presented and that nonsensical part of the conclusion made me wonder.

The study's stated goal was to "examine relationships between prenatal and infant ethylmercury exposure from  vaccines and/or immunoglobulin preparations and ASD and 2 ASD subcategories: autistic disorder (AD) and ASD with regression."

To do that they looked through the health records for three HMOs, found all of the kids born between 1994 and 1999 that had a label of autism, and attempted to get them to participate in the study.  They started out with 802 children with autism but ended up only including 256 of them in the final results.  These children were matched against 70,801 potential control children with 762 being the final number of controls.  The control children were pretty well matched against children with autism on a variety of factors such as birth year, gender, weight at birth, parent's age, mother's education level, as well as other factors.

The cumulative exposure to thimerosal was then calculated for three time periods - birth to 1 month, birth to 7 months, and birth to 20 months.  These exposures (along with a bunch of other data) were put into a variety of models and no relationship between the level of thimerosal exposure and autism was found.

But, if you are paying attention, you might have noticed a problem.  The goal of the study was to look for a relationship between thimerosal and autism - not to look at the relative risk from a higher thimerosal exposure.  Yet, it is that second question that was the one actually addressed.

Let me put this another way.  If I told you that I was doing a study to evaluate whether smoking can cause cancer but instead gave you a study that compared people who smoked one pack a day to those who smoked two packs a day.  Then, when I found no increased risk of cancer between the two groups, I said that my study showed no relationship between cancer and smoking.  While it might be true that smoking more does not lead to a higher risk of cancer that is not the same as saying that smoking at all doesn't increase the risk of cancer.  When you compare cancer rates in smokers vs non-smokers the association jumps out.

Those of you who know the history of the tobacco research would recognize that studies like this were actually used by industry to obscure the relationship between smoking and cancer.  But I didn't want to think that the CDC would put out such a distorted study, so I looked at the actual numbers a bit closer.

There are two measures of risk in the study.  The first is an odds ratio associated with an increase of 1 unit (1 mcg per 1 kg) of exposure.  That measure is clearly looking at whether more thimerosal means more autism, not whether thimerosal has a relationship to autism.

The second measure was an odds ratio between a low and high exposure group.  The low exposure group is defined to be (roughly) the children in the bottom 10% while the high exposure group is defined to be the children in the top 90% group.  The question then becomes what is the actual difference in exposures between these groups.

Are we talking about groups where the "low" exposure group had 5 shots vs the "high" exposure group getting 6 or are we talking about groups where the low exposure group basically have no exposure while the high exposure group had close to the maximum.  The former comparison would be worthless while the later would be close to what we would want to see.

Here is where things got a little confusing.

The ranges between high and low are quoted in mcg per kg but the data published for the groups is quoted in cumulative mcg.  For the birth to 1 month value is 4.08 mcg/kg which roughly translates into about 16 mcg of exposure - or about one shot.  Then I looked at the exposure table - the range for birth to 1 month group was 0 to 74 with a mean of 2.7 for the autism group and 0 to 100 with a mean of 2.35 for the control groups.  But how can the mean for the groups be that much less than one shot (12.5 mcg) and why does the control group have a higher maximum than the autism group?

For the birth to 7 month and birth to 20 month groups a similar pattern plays out.  The range between the groups seems to get a little larger (about 125 mcg and 200 mcg, respectively) but the ranges and mean seem to be strange.  All of the groups for all of the time frames have a minimum of zero exposure, so does that mean that the low exposure groups were primarily made up of children with no exposure to thimerosal?

The study doesn't really go into any details about the composition of the high and low exposure groups.  But then I remembered there was a reference about supplemental data and went looking for it.  Typically the supplemental data will contain some of the extra data that didn't fit in the study because of space constraints, and I thought it might be able to shed some light on the subject.

Well, I found the supplemental data here and here - all 387 (!) page of it.  I have never seen a study with this much supplemental data in it.  But even more interesting was were I found it, on the web site of Abt Associates.

It turns out that the majority of the work for the study was not done by the CDC but rather a private company.  This is kind-of mentioned in the study but it doesn't really call out the fact that "one of the largest for-profit government and business research and consulting firms in the world" did the work for the study nor that "in 2008, Abt Associates was ranked 20th among the top 50 U.S. market research firms by the American Marketing Association."

It is possible that the answer to the my question is buried in the supplemental data but I don't have the time (or desire) to read through almost 400 pages to find the answer.  The results of the study are somewhat confusing but the sheer amount of data that was dumped along with it makes it that much harder to get at what question was actually answered or what the results actually mean.

I am beginning to suspect that was the point.