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What is Causing the Increase in Autism Prevalence?

October 22, 2010 39 comments

“Got Questions?” is a new weekly feature on our blog to address the desire for scientific understanding in our community.  We received over 3000 responses when we asked what science questions were on your mind. We answered a few here and will address the other themes we received in this weekly post.

In the last two decades, autism prevalence as reported in the scientific literature has increased by more than 600%.  In 2009, the latest estimate of autism prevalence in the United States, as reported by the Centers for Disease Control was 1 in 110 children[1].  Since then, a number of studies have sought to investigate the cause(s) of this dramatic increase in autism prevalence over time.  The most recent findings suggest that at least a portion of the increase in prevalence can be attributed to changes in diagnostic practices and increased awareness of autism over time, as well as other social factors such as advanced parental age.  However, converging evidence also suggests that while these factors account for a portion of the increase, they cannot alone explain the dramatic rise in autism prevalence.

The criteria for assessing autism has changed over the last 20 years resulting in a broadening of autism diagnoses and the identification of cases that would not have been diagnosed as such using older criteria. Looking at a population of children in California, researchers from Columbia University reported[2] that approximately 26% of the rise in autism caseload between 1992 and 2005 could be directly attributed to changes in diagnostic criteria, specifically the shift from mental retardation diagnoses to autism diagnoses.  In other words, 1 in 4 children diagnosed with autism in California today would not have been diagnosed using older diagnostic criteria.

Another aspect of the autism landscape that has changed over the past 20 years is an increase in the awareness of autism among the general public as well as healthcare professionals. In 2010, the Columbia University research team again examined[3] the California sample in an effort to quantify the influence of autism awareness on the rise in autism prevalence.  The investigators found that children living in close proximity to another child that had been previously diagnosed with autism had a better chance of being diagnosed with autism themselves.  The proposed explanation is information diffusion, or parents talking to and educating other parents about autism resulting in an increased likelihood of their children being diagnosed.  It is estimated that 16% of the increase in autism prevalence over time in California was due to social influence and increased awareness.

An additional social factor that has been implicated in contributing to the increase in autism prevalence is advanced parental age.  A number of recent publications investigating the relationship between parental age and autism have demonstrated that older parents are at increased risk for having a child with autism. This is not surprising since increased parental age is associated with a slightly increased risk for other developmental disorders as well.  Researchers from the California Department of Public Health reported[4] that parental age and particularly maternal age is a significant risk factor for autism, with a 10-year increase in maternal age increasing the odds of having a child with autism by 38% and mothers over the age of 40 at highest risk.  Researchers at Columbia University similarly found[5],[6] that older mothers and fathers were at increased risk of having a child with autism and estimated that the increase in parental age over time can account for 11% of the increase in prevalence over the same time period.  The underlying mechanism behind the relationship between increased parental age and risk for autism is currently under investigation.

Based on the abovementioned research, approximately 53% percent of the increase in autism prevalence over time may be explained by changes in diagnosis (26%), greater awareness (16%), and an increase in parental age (11%).  While this research is beginning to help us understand the increase in autism prevalence, half of the increase is still unexplained and not due to better diagnosis, greater awareness, and social factors alone. Environmental factors, and their interactions with genetic susceptibilities, are likely contributors to increase in prevalence and are the subject of numerous research projects currently supported by Autism Speaks.

The increase in autism prevalence is real and the public health crisis is growing. More families are affected by autism today then ever before.  While Autism Speaks has cast a wide net to explore the role of genetic and environmental factors in increasing the risk for autism, the research community requires additional funding support to increase the pace of discovery. Never before has the need for research into the causes of autism and effective treatments for autism been greater.


[1] Prevalence of Autism Spectrum Disorders – Autism and Developmental Disabilities Monitoring Network, United States, 2006. Morbidity and Mortality Weekly Report. 2009;58(SS-10). http://www.ncbi.nlm.nih.gov/pubmed/20023608

[2] King, M. & Bearman, P. (2009). Diagnostic Change and Increased Prevalence of Autism. International Journal of Epidemiology, Volume 38, Issue 5:1224-1234.

[3] Liu, K., King, M., & Bearman, P. (2010). Social Influence and the Autism Epidemic. American Journal of Sociology, Volume 115, Number 5:1387-1434.

[4] Grether, et al. Risk of Autism and Increasing Maternal and Paternal Age in a Large North American Population. American Journal of Epidemiology. 2009;170(9):1118-26. http://www.ncbi.nlm.nih.gov/pubmed/19783586

[5] Liu, K., Zerubavel, N., & Bearman, P. (2010). Social Demographic Change and Autism. Demography, Volume 47, Issue 2:327-343

[6] King, M., Fountain, C., Dakhlallah, D., & Bearman, P. (2009) Estimated Autism Risk and Older Reproductive Age. American Journal of Public Health, Volume 99, Issue 9:1673-1679.

Categories: Got Questions?, Science Tags: ,

5|25: Celebrating Five Years of Autism Science Day 25: Autism Prevalence Reaches 1:110

February 25, 2010 Leave a comment

In honor of the anniversary of Autism Speaks’ founding on Feb 25, for the next 25 days we will be sharing stories about the many significant scientific advances that have occurred during our first five years together. Our 25th item, Autism Prevalence Reaches 1:110, is from Autism Speaks’ Top 10 Autism Research Events of 2009. 

In 2009, two major studies using different research methodologies yielded strikingly similar and eye-opening results showing that ASD affects approximately 1% of children in the United States. Based on data collected just four years earlier, it was found that ASD affected 1 out of every 150 children in the U.S. This represents a 57% increase in ASD prevalence in a relatively short period of time. Both studies also found that ASD continues to be four times more common in boys than girls.

In the first study, published in Pediatrics, authors from the U.S. Department of Health and Human Services (HHS) and the Centers for Disease Control and Prevention (CDC) collected data through the National Survey of Children’s Health (NSCH) on parent-reported diagnosis of ASD. Among a nationally representative sample of 78,000 children aged 3 to 17 years, the investigators found that 1 in 91, or an estimated 673,000 children in the U.S. had an ASD. While concerns lingered over the parent-reported nature of the data, this large-scale study set the stage for another major publication on ASD prevalence with similar results.

In December researchers at the CDC released new prevalence data collected by the Autism and Developmental Disabilities Monitoring Network (ADDM), a series of surveillance sites throughout the U.S. that maintain medical and service records on children with autism. By abstracting data and subjecting those records to stringent clinical evaluation, the authors found that approximately 1 in 110 children, 1 in 70 boys, met the criteria for ASD. This 1 in 110 statistic, based on data collected in 2006, represents a 57% increase from the 1 in 150 statistic which was based on data collected by the ADDM network in 2002 using identical research methods to the current study.

In a year that was jam-packed with publications on autism epidemiology, a number of other studies sought to investigate the reasons for the dramatic increase witnessed in autism prevalence. Researchers from Columbia University reported that approximately 25% of the rise in autism caseload in California between 1992 and 2005 could be directly attributed to changes in diagnostic criteria that resulted in a shift from mental retardation diagnosis to autism diagnosis. Therefore, converging evidence from this study and others around the world suggests that while changes in diagnostic practice may account for a portion of the increase, they cannot alone explain the rise in autism prevalence, and other factors, including environmental factors, likely play a role. One environmental factor that continues to be implicated in the increase in autism prevalence is parental age. Researchers from the California Department of Public Health reported in 2009 that parental age and particularly maternal age is a significant risk factor for autism, with a 10-year increase in maternal age increasing the odds of having a child with autism by 38% and mothers over the age of 40 at highest risk.

The prevalence studies of 2009 helped shed additional light on the immense nature of the autism public health crisis. With 1% of the U.S. population affected by ASD, and emerging data suggesting that 1% of the global population may be affected by ASD, never has the need for funding to support research into the causes and treatments of ASD been greater. In addition, these findings call attention to the necessity for more accessible diagnostic and intervention services for the growing population of those affected. In the CDC’s ADDM report and a separate study published in the Journal of the American Academy of Child and Adolescent Psychiatry, it was reported that while we can now reliably diagnosis autism spectrum disorders at two years of age, children on average are still being diagnosed at close to 6 years of age. This means that there is a large gap between the time that children can effectively be diagnosed at age 2, and the time they are actually receiving a diagnosis – valuable time lost where early intervention services can dramatically improve outcomes.

Did you know?: Autism Speaks, in partnership with the CDC, developed the International Autism Epidemiology Network, a forum to facilitate collaboration and information sharing between autism experts around the globe. Launched at the International Meeting for Autism Research (IMFAR) in May of 2005, today the network supports over 100 participants from 30 countries and its activities have resulted in over $2.5 million in targeted international epidemiology research funding from Autism Speaks. This includes the launch of two RFAs in 2008 designed specifically to better understand global autism prevalence and risk factors – click here for more information on the funded grants.

What is Causing Autism Prevalence to Increase? – Part 2

January 8, 2010 Leave a comment

This part 2 of a 2 part series is from Michael Rosanoff and Andy Shih, Ph.D. who both work in the Autism Speaks science department. This second post is from Andy Shih. Both guest bloggers bios are below the post.

The release of the latest prevalence data by the CDC last week was important in two ways.  One, of course, is its implication for the role of environmental risk factors in autism. The other is how the finding enhances awareness and supports our call for more money for research.

The same can be said for our international epidemiology efforts. As part of our Global Autism Public Health initiative (GAPH), we have been funding and planning prevalence studies with our international partners and colleagues for the past several years. In South Korea, for instance, we are expecting the publication of the first ever prevalence estimate in early 2010. We also have prevalence studies in various stages of development in Albania, India, Ireland and Mexico.  All these efforts involve members of our International Autism Epidemiology Network.

In addition to the contributions these studies can make to our understanding of autism, they will also help raise awareness and inform policy development in parts of the world where affected individuals and families struggle with severe stigma, and in many instances, little or no support and care.  Another way to look at it is that when you conduct a prevalence study, you are basically asking members of the autism community to stand up and be counted. When that happens, especially if the number is anywhere close to the 1 percent figure we have here in the States, their plight and needs can no longer be ignored.

Author Bios

Andy Shih

Andy Shih, Ph.D. is the Vice President of Scientific Affairs at Autism Speaks, where he oversees the etiology portfolio, which includes research in genetics, environmental sciences, and epidemiology. He was responsible for the formation and development of Autism Speaks sponsored international autism research collaborations, the Autism Genome Project and the Baby Siblings Research Consortium. Andy also leads Autism Speaks’ international scientific development efforts, such as the Global Autism Public Health Initiative (GAPH). Andy joined the National Alliance for Autism Research (NAAR) in 2002.

Prior to joining NAAR, Andy had served as an industry consultant and was a member of the faculty at Yeshiva University and New York University Medical Center. He earned his Ph.D. in cellular and molecular biology from New York University Medical Center.

Andy’s research background includes published studies in gene identification and characterization, virus-cell interaction, and cell-cycle regulation. He was instrumental in the cloning of a family of small GTPases involved in cell-cycle control and nuclear transport, and holds three patents on nucleic acids-based diagnostics and therapeutics. Andy is a resident of Queens, where he lives with his wife, daughter and son.

Michael Rosanoff

Michael Rosanoff, MPH, is a member of Autism Speaks etiology team and manages the organization’s epidemiology and public heath research grants. Since joining the organization in 2007, Michael has been the staff lead in overseeing the International Autism Epidemiology Network (IAEN) and is part of the development team for the Global Autism Public Health Initiative (GAPH). He is also a member of Autism Speaks Grants Division, helping oversee the administration of the organization’s grant-making process for research.

Prior to joining Autism Speaks, Michael conducted independent research at the Gertrude H. Sergievsky Center, a clinical, epidemiological and genetic research center at Columbia University Medical Center focused on developmental disorders of the nervous system. His research background is in genetic and psychiatric epidemiology as well as behavioral neuroscience and neuroimmunology, with publications in the fields of epilepsy and depression. Michael earned his Master of Public Health (MPH) in epidemiology from Columbia University’s Mailman School of Public Health and resides in N.J.

What is Causing Autism Prevalence to Increase? – Part 1

January 6, 2010 Leave a comment

This part 1 of a 2 part series is from Michael Rosanoff and Andy Shih who both work in the Autism Speaks science department. The first post is from Michael Rosanoff. Both guest bloggers bios are below the post.

It’s been just over a week but by now most of us have heard that the new autism statistics are out and no less frightening – 1 percent. So the question on everyone’s mind is what is causing this astounding increase in prevalence? Fortunately, in addition to measuring how prevalent autism is in a population, epidemiology can help piece together the rest of the puzzle by examining what is causing autism to be so prevalent. Part of the approach is to tease out some of the “non-casual” factors contributing to the increase over time such as changes in how autism is diagnosed and increasing awareness. While we can’t yet see the full picture, recent research from the U.S. and around the world is showing us that while these factors are clearly playing a role in the rise in autism prevalence, they cannot account for the dramatic increase alone. Epidemiology research can shed light on some of the genetic and environmental factors driving this rise in prevalence, and once we uncover the causes or risk-factors, we can more effectively develop ways to manage this growing problem.

Currently, Autism Speaks is supporting and advising on a number of large-scale epidemiology studies in the U.S. that look at environmental factors potentially contributing to the rise in autism prevalence. These include the EARLI Study, CHARGE, and the National Children’s Study.  In addition, international epidemiology research has been an area of major focus for Autism Speaks. In 2004, Autism Speaks and the CDC (in fact, the authors of the latest prevalence study) co-developed the International Autism Epidemiology Network to promote collaboration and facilitate research among autism epidemiologists worldwide. Today, the network includes over 100 scientists from more than 30 countries.

International research presents unique opportunities to understand the etiology, or causes, of autism by studying different ethnic groups in countries with different environmental conditions than found in the U.S. alone. Epidemiologists can make comparisons of autism prevalence across nations as a means of generating clues about the involvement of genes or environmental exposures. Additionally, some nations have special resources, such as health registries and surveillance systems that can generate large datasets and make previously impossible studies on autism possible. Autism Speaks is currently supporting the iCARE project which combines data from Norway, Sweden, Denmark, Finland, Israel, and Australia to investigate pre- and peri-natal risk factors for autism.

So what we have now is mounting evidence that autism is a major public health issue and epidemiologists have the tools to investigate why autism is more prevalent now than ever before.  The question remaining is what are we going to do about it?  How are we going to enable the necessary research? Autism Speaks is answering the call through our supported research efforts, but our efforts alone are simply not enough to help the 1 percent of the U.S. and possibly global population affected by autism. We need answers and with more support, research will provide the answers families need.

Author Bios

Andy Shih, Ph.D., Vice President of Scientific Affairs at Autism Speaks

Andy Shih, Ph.D. is the Vice President of Scientific Affairs at Autism Speaks, where he oversees the etiology portfolio, which includes research in genetics, environmental sciences, and epidemiology. He was responsible for the formation and development of Autism Speaks sponsored international autism research collaborations, the Autism Genome Project and the Baby Siblings Research Consortium. Andy also leads Autism Speaks’ international scientific development efforts, such as the Global Autism Public Health Initiative (GAPH). Andy joined the National Alliance for Autism Research (NAAR) in 2002.

Prior to joining NAAR, Andy had served as an industry consultant and was a member of the faculty at Yeshiva University and New York University Medical Center. He earned his Ph.D. in cellular and molecular biology from New York University Medical Center.

Andy’s research background includes published studies in gene identification and characterization, virus-cell interaction, and cell-cycle regulation. He was instrumental in the cloning of a family of small GTPases involved in cell-cycle control and nuclear transport, and holds three patents on nucleic acids-based diagnostics and therapeutics. Andy is a resident of Queens, where he lives with his wife, daughter and son.

Michael Rosanoff, Assistant Director of Public Health Research and Scientific Review

Michael Rosanoff, MPH, is a member of Autism Speaks etiology team and manages the organization’s epidemiology and public heath research grants.  Since joining the organization in 2007, Michael has been the staff lead in overseeing the International Autism Epidemiology Network (IAEN) and is part of the development team for the Global Autism Public Health Initiative (GAPH). He is also a member of Autism Speaks Grants Division, helping oversee the administration of the organization’s grant-making process for research.

Prior to joining Autism Speaks, Michael conducted independent research at the Gertrude H. Sergievsky Center, a clinical, epidemiological and genetic research center at Columbia University Medical Center focused on developmental disorders of the nervous system. His research background is in genetic and psychiatric epidemiology as well as behavioral neuroscience, with publications in the fields of epilepsy and depression. Michael earned his Master of Public Health (M.P.H.) in epidemiology from Columbia University’s Mailman School of Public Health and currently resides in Jersey City, N.J.

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