Thursday, December 9, 2010

Autism Prevalence Mashup

Perhaps the most important unresolved question today about autism is whether it is becoming more common.  Are we in the midst of an epidemic of autism or are social forces just making it appear that way.  The answer to this question has the potential to reshape how we think about autism and how we should deal with it.

If the rate of autism is not increasing then our focus should be on providing services and finding new ways to help people with autism live more productive lives.  But, if the rate of autism is increasing, then our immediate concern should be figuring out why and putting a stop to it.

While I don't think there is yet a clear answer to the overall question, I think it is safe to say that the number of children with a label of autism is increasing each year.  The problem is trying to figure out if this increase is real or not.

Since I think the question is important, I decided to take some administrative prevalence data from studies that I was reading and put them together to see what they looked like.  The papers are both about autism prevalence in Montreal, Canada and both use yearly administrative data from school boards to estimate the prevalence of autism.

There are several problems with what I am going to talk about below, so let me get those out of the way.  First, the general disclaimers about administrative prevalence apply - so yes, I know that there are problems with using this type of data.  Second, the papers used two different school boards so there is a problem with combining the data like I am doing.  But, since both of the school boards are in the Montreal area and both used the same definition of autism, I think the comparison has some relevance.

So, without further ado, I give you the first chart.  The years on the bottom are the birth year of the children.  Keep in mind that the age of the children is going from the youngest on being on the right (2002) and the oldest being on the left (1987).

Although, the birth years aren't really exact birth years but rather an approximation based on what grade the child was in.  So if a child was held back a grade or two as might be common for children with special needs (if that even happens in Montreal, I don't know), then the ages could be skewed.

The blue line represents the children from the first study and the green line represents the children from the second.  I indicated the point at which the children on both lines would have been eight years old.  That can be important because that is the age where we can assume that most children with autism have been recognized and given the appropriate label.

The red line is a three period moving average of both lines and represents the overall trend of the numbers.

(Click for a larger version)
I think there are a few notable things on this chart.

First, I think the overall trend is clear.  Younger children are more likely to have a label of autism than older ones and the number of children with an autism label is growing by about ten percent per year.

Second, notice that the prevalence goes up as the children get younger up until age eight when it starts to fall? This is what I was talking about above where younger children might not yet have a diagnosis, so we can assume that the numbers before age eight are lower than they should be.

Third, if you look at where the blue and green lines overlap, you might notice that the rate of autism in the children from the second study is about half of that from the earlier study.  For example, in 1993 the children in the earlier study were about ten years old and had a rate of about 71 per 10,000 but in the second study the children would have been 15 and had a rate of about 48 per 10,000.

As I have commented on before, it looks like there might be a substantial group of children who have a diagnosis of autism when they are younger but lose it as they get older.  This is the third independent data set where I have seen this relationship and I am starting to wonder about it.  If I am not mistaken, this rate is similar to the recovery rate that has been historically demonstrated for ABA.

Moving on, another nice thing about these two studies is that they gave a breakdown between the different types of autism.  One of the theories about the increasing rate of autism is that, as time goes on, there are more milder cases being recognized and that is partially responsible for the increase.  But, as you can see on the chart below, that didn't happen here.

(Click for a larger version)
Even though the average prevalence increased between the two studies, the breakdown of the types of autism is essentially unchanged.  The majority of autism cases here are PDD-NOS, followed by classic autism, and finally Aspergers bring up the rear.  And, as I talked about before, CDD is extremely rare with only 1 child having that label.

Take away from this what you will, I just found it to be interesting.  Or maybe this is a sign that I need to get a better hobby...


References

1. Fombonne, Eric, Rita Zakarian, Andrew Bennett, Linyan Meng, and Diane McLean-Heywood. 2006. “Pervasive developmental disorders in Montreal, Quebec, Canada: prevalence and links with immunizations.” Pediatrics 118:e139-50.  doi: 10.1542/peds.2005-2993

2. Lazoff, Tamara, Lihong Zhong, Tania Piperni, and Eric Fombonne. 2010. “Prevalence of pervasive developmental disorders among children at the english montreal school board.” Canadian journal of psychiatry. Revue canadienne de psychiatrie 55:715-20. Link

7 comments:

  1. But, if the rate of autism is increasing, then our immediate concern should be figuring out why and putting a stop to it.

    One reason might be increasing paternal age and it might be hard to convince men over 40 not to have kids. Other than this, I don't think anything definitive in the environment or anywhere else might be contributing to the increase has been found except maybe more breech deliveries and increases in cesarean sections, but not sure if anything can be done about these.

    So if a child was held back a grade or two as might be common for children with special needs (if that even happens in Montreal, I don't know), then the ages could be skewed.

    I was put in the 8th grade at age 14 when I was first mainstreamed in regular school, a year behind my typical birth cohort.

    It also appears from these studies the prevalence in canada might be higher in the u.s. as it is apparently as high as 140/10,000 for younger children (assuming I am reading the charts correctly). According to CDC data, is less than 100/10,000 for kids here, though that is just an average of different states whose prevalence is variable.

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  2. Well considering my eldest's ABA has been Ont PPM 140, which is teaching social and behavioural skills not "training"... I beg to differ on the "see ABA works" theory since they didn't start helping him until Gr 4 at which time they offered to change his dx from "a mild form of ASD" to "mild NLD"....

    See... I'm not convinced autism is growing. It is a well known - but not said out loud outside of 1:1 conversations - fact that services at this time are only available to those with severe impairments or autism. So, if you can get a child dx'd with autism, you keep the dx as long as you can.

    My eldest was dx'd at 2.5 with non-verbal PDD. At 3 with "speech and language delayed with global delays"... at 5 I was told "that's just a learning dx and we don't have to do anything until Gr 3" by the school. 18mths back through the medical system and it reads "a mild form of ASD" or verbally "NLD w/ S/L delay"... With autism we get OT, we get a quarter time aide, we get a fusion keywriter and we get a child that is doing well in Gr 6. We remove autism we get NOTHING.

    Professionals know this, parents know this.... but as they say "the squeaky wheel...." and autism is currently the squeakiest... and that's where the services are. While others are ignored.

    http://www.cbc.ca/health/story/2010/10/27/adhd-schools.html

    So, do you dx your child with mild autism or adhd????? IMO, the one that get's the child the services they require.

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  3. Jonathan,

    I think there are many chemicals in the environment that have the potential to cause autism. For example, any of the endocrine disrupting chemicals have the potential to cause havoc that might lead to autism. Or there could be a relation with pesticides or something like that. But you are right that no definitive relationship has been shown yet.

    The prevalence in Canada is (from what I understand) about the same as it is in the US. The same sort of spike is seen in the younger children in the US. For example, look at the chart linked below that is based on NSCH data from 2007 -

    http://4.bp.blogspot.com/_WoSi1HFMqsc/So9ihNVyK-I/AAAAAAAAAAc/gnHTZ2fRB8Y/s1600-h/NSCH.gif

    There are many age groups that are close to the 140 mark as of 2007 and 7 year olds are quite a bit above it. The sample behind the 2007 study is quite a bit larger than the single school boards above so it has the potential to be more accurate.

    Whatever the true number is though, the youngest generations (my children's age) do see to have a higher prevalence than the current 1 in 110 figure for the CDC. I expect the next figure released from from CDC in a couple of years will be about 1 in 90.

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  4. Farmwifetwo,

    While I agree that there is some creating labeling going on I don't know how much of the increase is being caused by that. If it were happening in a large number of children then there should be a corresponding decrease in the use of other labels. But I have never seen anyone who was able to demonstrate a large enough decrease.

    And, in the US at least, there are somewhat decent services for most of the major disabilities (depending on where you live). It is my impression that parents here have to fight harder for appropriate autism services than they would for other disabilities such as ADHD.

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  5. I think there are many chemicals in the environment that have the potential to cause autism. For example, any of the endocrine disrupting chemicals have the potential to cause havoc that might lead to autism. Or there could be a relation with pesticides or something like that. But you are right that no definitive relationship has been shown yet.

    You want to make the emphasis on potential to cause autism which is a possibility I suppose but I don't think anything has ever been shown.

    It is improbable that pesticides have any relationship with autism as the prevelance of autism seems to vary a lot from area to area, including various parts of California where I live. Pesticides are more commonly used in rural and farm areas, yet more rural states seem to have lower prevalence rates according to the CDC and the California figures (administrative) which were once compiled show that the prevalence rates are much lower in northern california than they are in metropolitan cities such as Los Angeles and San Diego.

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  6. You are that correct any relationship between environmental chemicals and autism are potential or possible relationships at best. There are some hints here and there that could be a relationship but nothing that approaches any reasonable standard of proof.

    For pesticides you have to be careful what exposures you are thinking about. The primary source of pesticide exposure would be from the foods that you eat, not from being in the area when then are sprayed. That sort of relationship would not be seen when looking at geographic areas.

    And then there are the few recent results that did show a show a correlation between a person's pesticide levels and ADHD.

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  7. Hello friends -

    Regarding pesticides, we do have some evidence of a possible contributory participant, from several lines of interest.

    This is a spatial study that found as proximity to fields sprayed with pesticides decreased, risk of autism increased.

    http://www.ncbi.nlm.nih.gov/pubmed/17938740

    There are also several studies that provide insight into how the autism group might be a susceptible subgroup to certain types of chemicals in pesticides. The genetic studies looking for known alleles that result in decreased paraoxonase (a detoxifying agent known to be involved in removal of organophosphates found in some pesticides) are mixed, but biomarker studies do seem to consistently find that by one way or another, the levels of this enzyme is decreased in autism populations.

    http://www.ncbi.nlm.nih.gov/pubmed/16027737

    http://www.ncbi.nlm.nih.gov/pubmed/20488557

    http://www.ncbi.nlm.nih.gov/pubmed/18624774

    The logical jumps shouldn't be too difficult to arrive at; these chemicals achieve their pest killing effects by interferring with nervous system function. Tinkering around with the developing neural structure doesn't seem very difficult to envision; espeically considering the rather robust findings associating pesticides and ADHD recently published in Pediatrics.

    http://pediatrics.aappublications.org/cgi/content/abstract/peds.2009-3058v1

    - pD

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