Home > Science > Evaluating Change in Autism Prevalence: Change We Can Believe In?

Evaluating Change in Autism Prevalence: Change We Can Believe In?

This post is by Alycia Halladay and Michael Rosanoff, members of the Autism Speaks Science Team.

Twenty years ago, autism affected somewhere around 1 in 2000 children.  Today, it affects 1 in 110 children.  In other words, autism prevalence has increased dramatically over the past 20 years.  In fact, it has increased an estimated 600%.  Seems straightforward enough, yet why do we keep hearing the same question…

“But is it a true change in autism prevalence?”  That is, how much of the change in autism prevalence is truly due to an increase in autism risk?

In an effort to uncover the answers to this question, Autism Speaks and the CDC co-sponsored a workshop entitled “U.S. Data to Evaluate Changes in the Prevalence of Autism Spectrum Disorders,” held on February 1, 2011 at the CDC Headquarters in Atlanta, GA.

The “Evaluating Change” workshop was designed to bring together stakeholders from the autism community and thought leaders in the fields of autism epidemiology and public health to consider the factors driving the change in autism prevalence over the past two decades.  A growing body of epidemiologic research has begun to piece together the prevalence puzzle.  Factors such as younger age of diagnosis, broadening of diagnostic criteria, improvements in the availability of services, and better awareness of the disorder have all been attributed to the change in autism prevalence.  However, recent epidemiological studies indicated that, while these factors do account for a portion of the change, they cannot account for all of the increase alone (see Figure which was adapted from a presentation by Dr. Peter Bearman at the meeting).

So, where is the rest of the increase coming from?  What is causing it?  And most importantly, what can be done to identify and quantify the influence of multiple genetic and environmental risk factors, and their interaction, on the change in autism prevalence over time? (For more background, please see “What is Causing the Increase in Autism Prevalence”)

Scientists, advocates, family members, and individuals with autism alike served as expert panelists charged to identify promising directions, scientific priorities, and possible approaches for better understanding ASD prevalence trends in the U.S.  The beginning of the workshop focused on existing datasets that have been used to estimate autism prevalence and identify potential environmental risk factors associated with autism diagnosis.  These include:  the CDC’s Autism Developmental Disability Monitoring Network (ADDM), the California Department of Developmental Services (DDS) system, and Special Education data, as well as data from international health registries such as those from the Scandinavian countries.  These surveillance systems, while not designed to study the causes of autism, nonetheless have been helpful in identifying possible risk factors.  Not only have these resources provided information about the rising prevalence of autism, but they have also identified and replicated findings relating to parental age, obstetrical complications, certain chemical exposures and even genetic influences.

In addition to presentations on what has been already been done to understand reasons for ASD prevalence changes, examples of approaches to understanding prevalence changes from other health conditions were presented.  Scientists from the fields of cancer, Parkinson’s, asthma, and schizophrenia research presented methodologies and models for deciphering prevalence trends in their respective disorders and how these previous efforts may inform autism prevalence research.  In all cases it was found that changes in prevalence over time are often the result of a complex relationship between genetic and environmental risk factors, as well as factors related to diagnosis and awareness.

In the afternoon, participants broke out into discussion groups focused on the following topics:  1) How can prevalence information be used by stakeholders including parents, professionals, and policy makers?  2) What more  can be done with ADDM data?  3) Where are there other sources of data that can be used for prevalence estimates and 4) What else can be done to understand ASD trends?

As the discussions progressed, a number of overarching themes started to become clear.  Risk factors studied in isolation are going to underestimate their true influence.  They need to be studied in combination.  The influence of these risk factors is unlikely to be simply additive, and sometimes they will overlap.  Therefore, the field needs new analytic models that can study a combination of multiple genetic and environmental factors.  As Dr. Ezra Susser, from Columbia University said “It is helpful now not to look through the lenses of one side or the other, but rather both, and to use the information for better advocacy and awareness.“

Another participant, Dr. William McMahon from the University of Utah put it this way, “think of this black box of prevalence as a pinball machine.  You can’t predict the trajectory of the ball based on just one lever. There are dozens of other factors that influence where that ball is going to go”.

Other recurring themes included the need for data on well-defined autism phenotypes, as well as the importance of data quality and accuracy.

Throughout the meeting public attendees contributed their ideas through thoughtful, careful comments.  Stakeholders expressed their ideas and their hopes for the way prevalence data would be used – these included lingering and existing concerns about different environmental exposures, need for facilities for adults, societal treatment and acceptance, and reasons for differences in developmental patterns.

As understanding autism prevalence can help us identify priorities in research, services, outreach, and advocacy, the outcomes of this meeting will be published in a meeting report to inform future strategic planning.  This workshop was only a first step in better understanding the changes in autism prevalence over time and characterizing the potentially responsible risk factors.   Ultimately, as risk factors related to increased autism prevalence are uncovered and if those risk factors are modifiable, then researchers will have new targets for better treatments and prevention measures.  The bottom line is that the dramatic increase in the prevalence of autism calls for urgent action to understand why the increase in occurring.  It also underscores the crucial need for more and improved services to address the needs of people with autism spectrum disorders and their families.

  1. February 4, 2011 at 6:36 am

    Dear all,

    Thank you for these informative minutes from your February 2011 meeting. I think that the record-based epidemiology developed in Atlanta and later within ADDM is an important tool to monitor changes in the prevalence of ASD. However, there is one thing I really miss in the results produced by this methodology; it regards changes in the composition of population-based ASD samples. The literature predicts that as prevalence of ASD increases, the proportion of individuals with less severe autistic symptomatology will increase and so will the male/female ratio. Another prediction, related to the former, is that the proportion of individuals with intellectual disabilities and individuals with co-occurring “associated” medical conditions will decrease. Is this what is happening? If not, why?

    Best wishes,

  2. Katie Wright
    February 4, 2011 at 2:41 pm

    There were some excellent speakers at this meeting- namely Dr. Durkin and Dr. Hertiz-Pinchero.
    Unlike Dr. Bearman they found that only 4% of ASD’s increase could be accounted due to advanced parental age at that at least 50% of ASD’s increase was unexplained. Dr. HP is an innovative environmental epi. scientist, her conclusions make the most sense, at least to me.

    Dr. McMahon was extremely disappointing. He argued that more needs to be done to convince parents that researchers understand the science best. MacMahon “is tired” of parents questioning him. You know what I am tired of? Arrogance in the medical and research communities. When they have figured out what has caused this epidemic I will stop asking questions, until then it will questions and more questions Dr. MacMahon.

    I question the value of the Scandinavian birth registries. So much $ has been invested in these studies but they are small extremely homogenous, less environmentally toxic nations with varying vaccine schedules. Last year it came to light that Danish researchers had falsified data and stolen millions of CDC money. There is little to no ethical or consumer accountability in these Scandinavian research projects.

    Like most ASD families I would bet we need to see a bigger investment into potential environmental triggers and clusters in the USA. The CDC has been dragging their feet every step of the way, let’s hope this workshop persuades them to get into gear and move.

    I was glad to see a few stakeholders involved. Some, like Mark Blaxill, contributed tremendously to these discussion. Others like Roy Grinker and Eric London doubt there is any real increase in ASD at all. They represent a tiny % of families and are part of very small organizations. It is important that the CDC has meaningful stakeholder involvement next time.

    It was great that the meeting was available via the internet.

    February 4, 2011 at 10:29 pm

    As a retired medical research scientist, with friends whose families are affected by ASD, I am stunned that this is not the foremost medical issue of our time. I value the work you have done, and can only hope that the importance of this trend becomes more widely appreciated.

  4. April Reichstein
    February 7, 2011 at 3:15 pm

    As the mother of a son, age 31, who is mildly autistic, I question whether there is an increase in autism. Our son should have been diagnosed 30 years ago. He was diagnosed about 5 years ago.
    There is a tendency to over diagnose the latest “syndrome”.
    Too much emphasis is placed on people who are different – I have had several conversations with teachers over the years about accepting the fact that all the students are not going to behave in the same manner.
    This syndrome has been around for many years. How many families out there have the proverbial “odd ball uncle” in their family tree? On my dad’s side, one brother didn’t talk until he was 3 years old. My conversations with him in the past few years make me think he probably displayed other autistic traits. The same is true for an uncle of my mother.
    It will take some hard data to prove to me that autism has become epidemic.

  5. Richard Fauth
    February 8, 2011 at 10:01 pm

    Enough Katie- Environmental variables mean all variables in the environment. Clustering to determine what? What you and these other parents view of Autism being caused by some nefarious industrial chemical spewing money making cold hearted S.O.B. It is way past time that this bunch grew up. Nature is not this gentle, pristine, lilly white entity you believe in. Mankind is not the unabated evil doer you are so willing to believe. There are all kinds of toxins in this world-always have been. Of course we should look at manmade toxins-but not natural ones? There is a reason that the average age we live to is considerably past the thirty five that we used to-hundreds of years ago.

    Did you ever see a photo of a city a hundred and fifty years ago? So black with coal soot, full of dioxin. Heavy metals? They didnt know any better-they were all over the place.

    What about all the other environmental variables that aren’t chemical? One very respected neurologist thinks that it could be ultrasound use during pregnancy-that would fit with the rise, time wise.

    How about we try and use real science, and support real science when they achieve results. Major advances in human genetics, pluripotent stem cells,and knockout mice have come through over the past decade. Real drug trials underway due to this research.

    Or we could just keep harping on what some authors wrote in books about a “silent spring” and “evidence of harm”. How effective has that been? It isn’t the case that Environmental factors can’t be part or all of the explanation for autism’s cause. They most certainly can be. But we aren’t even close to finding anything there because the credibility of the vast majority of it is bunk.

    We need answers. Not agendas from a bunch of leaches sucking resources out of parents who are willing to believe, for decades, untruths. This is our kids we are talking about-not some contest to see who is right.

  6. Katie Wright
    February 9, 2011 at 11:18 am

    Richard aren’t you always saying that parents are not each other’s enemies? What I believe happened to my son is not a personal attack on you. We obviously disagree that’s fine.

    I listened to the entire conference and heard a number of things that rang false- specifically Dr. MacMahon’s commentary and the applicability of Scandinavian birth records. I also advocate for more environmental scientists, yes.

  7. February 9, 2011 at 2:06 pm

    Environmental factors along with children’s physical pre-disposition genentically combined with drugs/vaccines are obstrusive of natural processes. My daughter’s a
    shining example of what occurs under all of these circumstances and most of it is
    reversible with nutritional, psychological and physiological trearments. Our case
    has been published by the US DOE’s Exceptional Student program and proven to work
    when these implements are applied. We strive to help by converting our company to
    focus on the findings all over the world which we’re involved in-please take time
    and peruse our website. If we all align together we’ll change the court for kids!

  8. Richard Fauth
    February 9, 2011 at 9:24 pm

    OK Katie-I appologize if i made it personal. However,I’ve been fighting for real help for my son since the dx’s over six years ago. The arguments on the environmental front are the same now as they were then-but nothing has happened other than continuing to float theories that were espoused then. It is incredibly frustrating to me that so much time and energy continues to be applied with nothing resolved. My comments weren’t directed at which speaker you thought was good or bad- im ok with that. My comments were directed at an agenda that sounds a lot more like Earth Day 1977 than finding help for our children. What is going to be different pending the outcome of the cdc clustering studies? If the answer to that question is nothing-then why do the studies? If proving Global Warming causes Autism is the Agenda then look at what that would resolve-again is it nothing? We need effective treatments for our kids and clustering studies will not lead to these treatments. BTW i’m glad you read my previous posts. I agree with your assessment that over 50% of the increase is unexplained-i just think your definition of environmental causes ordains the outcome. I dont see how that helps.

  1. February 4, 2011 at 3:00 am

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