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Is autism more common today than 40 years ago?

40 years ago autism was thought of as the most well-defined, severe, and perhaps also the rarest child psychiatric disease. The prevalence was generally reported to be 0.01-0.04% of the child population. Today, several per cent of young people in Stockholm receive a diagnosis of autism. There is talk of an epidemic. How can this be explained? Has autism increased and, if so, what are the reasons behind the increase? These questions make up the theme of this edition of the “Researcher’s Corner”, in which we meet with Professor Christopher Gillberg to clarify the matter and find out more.

In Stockholm it was recently announced that several per cent of teenagers have autism and that there has been a considerable increase in recent years. But is there really proof that autism has become more common?

- It is correct that the diagnosis of autism is given very frequently in Stockholm and that it was given considerably less often ten years ago. This however, does not say anything about whether the constellation of symptoms that we call autism has actually become more common.

- There is strong support for autism being diagnosed more frequently, in fact the registered diagnosis of autism has increased more than a hundredfold since the late 1970s. There is however no convincing proof of the phenomenon of autism having become more common, if by autism we mean the combination of severe social and communication problems and ritualised repetitive behaviour.

How can the increase in diagnosed autism be explained?

- The view of what should be included in the autism diagnosis has changed quite a lot over the last thirty years. In the 1970s autism was thought to exist almost exclusively in individuals with general cognitive disability and at least three out of four of those receiving the diagnosis had an intellectual impairment equivalent to the level that in our current legislation would be labelled intellectual developmental disorder. Today, when it has become clear that what we often refer to as Asperger syndrome is part of the ”autism umbrella” (because the fundamental social communication and behavioural problems are identical to those seen in ”typical/classic autism”), it is more like one in ten to one in seven who have a tested IQ of around 70 or lower.

- We conducted studies as early as in the 1970s and found that classic autism was prevalent in 0.04% of children, but also studies that showed that pronounced autistic traits were prevalent in at least 0.7% of primary school children. These children with autistic traits today, without a doubt, would be given an autism diagnosis. In a recently conducted study by Gudrun Nygren and colleagues here at the Gillberg Centre, we found that 0.8% of preschool children fulfilled all the criteria for an autism diagnosis and in an equivalent study in Stockholm, Elisabeth Fernell and I found a prevalence of 0.6%. These studies – conducted over a period of more than 35 years – indicate that autism was as common in the 1970s as it is today.

Have you conducted any studies in recent years, which could shed light on the relationship between the phenomenon of autism and the diagnosis of autism?

- Yes, Sebastian Lundström and I have reviewed the results of the Child and Adolescent Twin Study in Sweden (CATSS) and data from the Swedish National Medical Care Register. The prevalence of the phenomenon of autism has remained fully stable just under one per cent of the child and adolescent population over the last decade. At the same time however the prevalence of the diagnosis of autism has multiplied. Hence this study suggests a seeming increase of autism in Swedish society, obtained through the diagnosis being given increasingly more frequently, even in such anomalies in children that, just a few years ago, no one would consider diagnosing as autism.

What do you think are the reasons behind this?

- Mild autistic traits are very common in the general population. Studies that Maj-Britt Posserud and I have conducted in Bergen show a prevalence of several per cent in school children. Such traits are generally not severely debilitating. It is likely that the most reasonable thing would be to regard these mild autistic traits more as a personality type or a ”cognitive type”. They do however occur more frequently in other debilitating conditions such as ADHD and language disorders. Perhaps it is almost exclusively when autistic traits – even when pronounced – are conjoined with such other problems that the total amount of problems becomes such that the support need becomes apparent and diagnosing becomes a way of getting appropriate interventions. Recently I have begun to refer to this group as “Autism Plus” to distinguish the clinically significant cases from “Autism Pure” (i.e. autism without comorbidity), which most often lack clinical importance, at least in early childhood.

- In practice, the interpreters of our Swedish legislation have decided that only the diagnoses of intellectual developmental disorder and autism constitute basis for getting access to habilitation services and other support measures according to LSS (The Swedish Act concerning Support and Service for Persons with Certain Functional Impairments). Children with for example ADHD (and some autistic traits) can have a very extensive need for support, but will be denied access to help, if they “only” have an ADHD diagnosis. If they instead were to receive an autism spectrum disorder or autism diagnosis various habilitating interventions would become available. I think many children with ESSENCE-related problems and only quite mild autistic symptoms today get an autism diagnosis as a means of ensuring that appropriate interventions can be offered to them and to their families.

Could it be that the prevalence of autism in society has indeed changed over time?

- There are multiple different causes behind Autism Plus, ranging from combinations of gene mutations and “major” chromosomal anomalies to the combination of gene mutations and biological environmental factors to biological environmental factors without autism genetic predisposition. We know that some infections during pregnancy (for example rubella) considerably increase the risk of autism. Some of these, previously common, causes of Autism Plus, have been reduced in frequency in the Western world, thereby decreasing the number of such cases of autism. At the same time the prevalence of extreme prematurity with survival beyond infancy has increased heavily. We know that factors linked to such extreme premature birth are strongly connected to Autism Plus. Hence: some forms of autism have decreased in frequency while others have increased. For these reasons the prevalence of Autism Plus should not be expected to be completely stable over longer periods of time or to be exactly the same in every corner of the world.

What conclusions do you draw from these research results?

- Autism Plus is an important clinical problem, which can be detected in preschool age. It is however not just (or perhaps not even predominantly) the autism that needs to be diagnosed and assessed in these cases but all the comorbidity (for instance intellectual disability, language disorder, epilepsy, ADHD) that comes with the autism. Early interventions should target all the difficulties, not only - which is currently often the case - the part of the problem that, on its own, could be called Autism Pure.

- We must achieve broad and comprehensive ESSENCE-teams, which integrate child neuropsychiatry/child psychiatry, child neurology and habilitation (and also include preschool and school participation) and which can accommodate families with children, adolescents and young adults with Autism Plus and other combinations of problems within the ESSENCE group.

- We must put an end to the overfocus on autism and intellectual developmental disorder solely. That is not to say that is not important to diagnose and intervene ”for” these types of problems, but that it is time for an individualised comprehensive approach with regard to resource allocation and organisation within the neurodevelopmental field.

By Nanna Gillberg




Page Manager: Anna Spyrou|Last update: 4/29/2014

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