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Rising awareness may explain spike in autism diagnoses

by  /  17 March 2014

Young boys continue to have the highest rate of autism diagnoses, but Danish doctors are diagnosing more girls, teenagers and adults with the disorder than they did in the mid-1990s. That’s the finding from a 16-year study published 20 February in the Journal of Autism and Developmental Disorders1.

Many studies look at the prevalence of autism, akin to taking a snapshot of the number of diagnoses in a given population. The new study instead examined the disorder’s incidence, or newly reported diagnoses, each year.  

Between 1995 and 2010, nearly 15,000 people received a new diagnosis of autism in Denmark, the study found. During that time, the incidence of autism overall increased from 9 diagnoses per 100,000 people to 38.6.

“We know that the incidence rates of autism spectrum disorders have increased in the last two decades, so we weren’t actually surprised about the increases,” says principal investigator Marlene Lauritsen, associate professor of child and adolescent psychiatry at Aalborg University in Denmark. “But we were surprised about most of the patients we saw the largest increases in.”

For instance, the number of males with a new autism diagnosis quadrupled from 13.2 per 100,000 people in 1995 to 58 in 2010. In the same time period, female diagnoses increased sevenfold from 2.6 to 18.6 per 100,000 people.

The greatest increase in incidence among girls came from diagnoses of two subcategories of autism, Asperger syndrome and pervasive developmental disorder-not otherwise specified (PDD-NOS). Both categories are being subsumed into the autism diagnosis in the newest edition of the Diagnostic and Statistical Manual (DSM-5), the American Psychiatric Association’s guidelines for diagnosis. And both are generally thought to represent the higher-functioning end of the autism spectrum.

“That is in a way interesting because it goes against the idea that girls are always more severely afflicted [than boys],” says Eric Fombonne, professor of psychiatry at Oregon Health and Science University, who was not involved in the research.

Incidence inquiry:

The researchers examined records from the Danish Psychiatric Central Research Registry, which contains reports on inpatient and outpatient care and diagnoses in Denmark.

To standardize the definition of autism spectrum disorders in the study, the researchers included only people up to 65 years of age who were diagnosed by a doctor using the tenth edition of the International Classification of Diseases, a publication of the World Health Organization and the DSM-5’s international counterpart. The ICD-10 was last revised in 1994 and still lists Asperger syndrome and PDD-NOS as diagnoses independent of autism. Its next edition is expected in 2017.

Boys are diagnosed more often than girls and at younger ages, the study found. On average, boys receive a diagnosis at 9 years versus an average of 11 years for girls.

In boys, the sharpest uptick over the study period is in childhood autism — a subtype of the disorder in which symptoms appear before 3 years of age — from 2.1 cases for every 100,000 people in 1995 to 17.6 in 2010. Another spike is in rates for PDD-NOS, which increased fivefold to 25.8 per 100,000.

In girls, new cases of PDD-NOS showed the steepest gains, jumping 11-fold from 0.8 cases to 9.3 per 100,000 people. Diagnoses of Asperger syndrome increased from 0.6 cases per 100,000 in 1995 to 5.8 in 2010.

Better diagnostic practices may explain these large hikes in incidence, says Maureen Durkin, professor of population health sciences and pediatrics at the University of Wisconsin in Madison.

“There’s much more awareness of autism,” say Durkin, who was not involved in the study. “There’s much more screening going on. And the newer generation of clinicians are being trained in this so they are more likely to see it.”

This increased attention to autism and its symptoms may also explain the rise in diagnoses of teenagers and adults.

Rapid growth: The fastest rise in new autism cases is in those diagnosed between 14 and 20 years of age, followed by adults diagnosed between 40 and 65 years of age.

An age-stratified analysis shows that children between the ages of 4 and 13 make up about 63 percent of the new autism cases. The fastest acceleration in new cases is in those diagnosed between 14 and 20 years of age.

Individuals diagnosed between 21 and 65 years of age account for about 9 percent of the new cases — but their proportion also significantly increased over the time frame of the study. Like girls, many of the adults are diagnosed with higher-functioning forms of autism, such as Asperger syndrome and PDD-NOS.

“If the incidence [in adults] is increasing, it just has to do with recognition of cases that have been missed up to that age,” Fombonne says. “It cannot be that you develop autism at age 50.”

Overall, PDD-NOS diagnoses show steep growth, just behind childhood autism. However, Lauritsen says, PDD-NOS is not as well defined as other autism subtypes such as Asperger syndrome.

“In [PDD-NOS], you can have children that we think are on the border of the autism spectrum,” she says. “We could think they are socially impaired, but it’s not quite clear that it’s autistic behavior.”

Individuals diagnosed with PDD-NOS often have social deficits but lack repetitive behaviors, a core symptom of autism. Studies suggest that under DSM-5 guidelines, some people with PDD-NOS would fall into a new category called social communication disorder rather than autism.


1: Jensen C.M. et al. J. Autism Dev. Disord. Epub ahead of print (2014) PubMed

14 responses to “Rising awareness may explain spike in autism diagnoses”

  1. Autismparent says:

    well there must be a split in opinion within the scientific community because researchers at UC Davis and officials at NIEHS have called the autism increase real and not the result of so called greater awareness or “better or substitute diagnosing”. Geri Dawson former head of Autism Speaks Science Division publically called the autism increase “alarming” and and epidemic” and Dr. Martha Herbert a neurologist and autism reseacher from Harvard University called the autism increase “a catastrophe”

    Autism Speaks said this:

    “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.

    Source: What is Causing the Increase in Autism Prevalence?” – Autism Speaks, October 2010

    • brian says:

      You quoted material suggesting that some years ago “half of the increase is still explained.” The paper discussed here represents an attempt to further our understanding and decrease the proportion of the apparent increase that is not unexplained. Why do you reject it

      • autismparent says:

        Some years ago?? The quote from Autism Speaks was written in 2010 only four years ago not decades ago. Furthermore, a recent University of Chicago study implicated environmental factors (toxins) as contributing to the autism increase. Last year Autism Speaks and UC Davis co-hosted a conferenece of the epigenetics of autism. Presenters refuted the idea that autism increase is only due to so called better diagnosing and maintain the increase is real. There are simply more children with autism than ever and that is not because doctors got really good at diagnosing it.

        I reject the better diagnoses/greater awareness idea because it implies the autism increase is not real but a result of better diagnosing- that people who would now be dxed were somehow overlooked in the past. Although people with autism existed in the past (1 in 10,000) we did not see them in these numbers now 1 in 88. Where are all the 1 in 88 autistics adults? I say they weren’t there in the past at least in the numbers we’re seeing today.

        I think we are seeing what should be normal chldren who early in life suffered a toxic expsoure leading to a disablity. These researchers should go out in the field and visit communties hard hit by autism or look at autism clusters like the Somali one in Minnesota- this is not normal. My street alone- 3 boys (my son included). My sons K-2 SPED class- 6 kids and that does not include the more severely autistic kids I see pull up in the van at his school everyday. There is no way you would have missed these kids.

        On SFARI, I see environmental factors being downplayed with the emphasis on put on genetics research. Autism is epigenetic. Even if a child has hidden genetic mutations something environmental is triggering expression of the mutation.

        I do not think researchers can have an honest conversation about the autism increase without including the environmental piece because that genetics is not the whole story. The majority of autism cases are epigenetic – an interplay between genes and the environment.

        “Environmental Epigenetics: New Frontiers in Autism Research” March 2013

        “Gene-environment interaction has important implications for autism causation research. We thank our participants, who are doing cutting-edge work in this emerging field, and invite you to learn more.”

  2. autismparent says:

    “Yet genetics alone cannot account for the majority of autism cases currently being diagnosed. There is lack of full concordance between monozygotic twins, with some estimate ranging as low as 60%, and the prevalence of ASD among siblings has been reported as high as 14%. Interactions among multiple genes are likely to contribute to various types of autism, and heritable epigenetic factors and/or non-heritable environmental exposures are likely to significantly contribute to susceptibility and variable expression of autism and autism-related traits. It is therefore likely that constellations of epigenetic and environmental factors are contributing to the increasing prevalence of ASD, a rise that cannot be fully accounted for by changes in diagnostic criteria.”

    Testimony of Dr. Isaac N. Pessah, Director, UC Davis Center for Children’s Environmental Health and Disease Prevention Professor of Toxicology

    TO: U.S. Senate Committee on Environment and Public Works

    Re: State of Research on Potential Environmental Health Factors With Autism and Related Neurodevelopment Disorders, August 3, 2010

    link to webcast of full hearing:

    • brian says:

      I don’t think that anyone with even a cursory understanding of embryology and genetics is surprised by the “lack of full concordance between monozygotic twins.” One barrier to understanding the “genetic” versus “environmental” contributions to the development of ASD must be in understanding what “environmental” influences act; in particular, a great deal of recent evidence suggests that early to mid-gestation is an important period in the development of ASD. You might be interested in material at this site that discusses, for example, somatic mutations in neurons early in prenatal development that could follow different paths in monozygotic twins, and in the clear developmental differences in monozygotic twins, including–for example–such obvious differences as birth weight.

      • autismparent says:

        While I think exposure of the parents over a lifetime or during pregnancy can affect genes, I am more interested in post natal exposures to our children. There does not seem to be a lot of research focus or money being channeled to post natal as compared to pre natal exposure that may result in autism.

  3. RAJensen says:

    Consistency of diagnostic schems over time has to be maintained. ICD-10 will be published in Oct. Sir Michael Rutter, the chairman of the working group on autism, has had his way. For the first time ICD-10 will not be following the diagnostic codes for autism published by DSM5. Rutter has dumped the DSM5 concept and the ICD-10 (2014) will be retaining separate diagnostic codes for Autistic Disorder, Asperger Syndrome, PDD/NOS unspecified and Childhood Disentigrative Disorder. DSM5 lumped all of these categories into a single Autism Spectrum Disorder category and created a new ambiguous and meaningless category of social communication disorder. Thanks to Dr. Rutter for his important work. This will keep diagnosis coding consistent over time and prevalence rates more reliable. ICD codes are used in the US over DSM which is a psychiatric manual not a medical manual. Here are ICD-10 (2014) diagnostic codes categories:

  4. ASD Dad says:

    I think anyone familiar with Autism epidemiology recognizes the muddle of conflicting figures that have emerged by varying researchers in differing populations and studying varying populations.

    Adding to the confusion is attempts by varying researchers to implement diagnosis of a disorder of early infancy and childhood to adults some 40 – 65 years after their birth.

    Does any of this make sense ? Not really

    It is now clear from many other areas of research that environmental and genetic factors are at play. The most recent research undertaken by University of Chicago strongly evidences environmental factors can play a cause with the focus being made previously in related research to pollutants , toxins , viruses and pesticides.

    The question has moved on from genetics v environment to a more focus ‘Which environmental factors ?”

    Those clues are provided both by elegant genetic work , physiological studies and neurology.

  5. AutismNewsBeat says:

    The CDC’s 2008 ADDM survey found an administrative prevalence among eight-year-olds of 1:88. But of that number, 20% had no previous autism diagnosis. This speaks to a large population of autistic people who are either undiagnosed or misdiagnosed. If this is the case, and it seems to be, then an increase in diagnoses is a good thing – it means more people who need support and accommodation can be helped.

  6. Amanda says:

    The problem is here is that while the diagnostic criteria for autism has been pulled much more tightly in the USA, the criteria for autism in Denmark has grown much more elastic. We are no longer comparing the same condition. There is no epidemic of 40 something year olds suddenly diagnosed with autism here. Clearly someone in Denmark who is socially awkward can receive a diagnosis of “autism.” This is not helpful to American research.

    We need to rethink our investments in international epidemiology. Such research from Denmark is not useful nor relevant to Americans.

    • ASD Dad says:

      Interesting comment Amanda in that latest research (above) the authors found …

      “The most striking negative effect was state regulation. State-mandated diagnosis of autism by a clinician for consideration in special education was linked with around a whopping 99 percent decrease in the rate of incidence for autism and ID.”

      Environmental factors accounted for a “283 percent for every one percent increase in frequency of malformations in a county.”

  7. SAM says:

    What complicates the matter is researchers sitting on boards of direction at various regulatory agencies with significant conflict of interest always finding ways tactics for minimizing this autism epidemic.

    Leo kanner for his orginal study for his first 10-12 studies had to go around the world to find his case studies. Today for the same number of individuals with autism, you need to go to the first public school near you.

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