Since the first documented cases of autism conditions by Leo Kanner in 1943 and Hans Asperger in 1944, conceptualization of autism spectrum disorders has shifted greatly. It is now evident that it is not a rare childhood disorder. In the 1990’s a marked rise in children being diagnosed sparked fears of an ‘autism epidemic’, increasing numbers diagnosed is a pattern which has continued today.
During the 1990s many made links between increased diagnosis of autism and the administration of MMR or other childhood vaccinations. Although these links have proven to be unfounded (Stehr-Green, Tull et al. 2003; Thompson, Price at al. 2007), the concerns regarding vaccinations have not yet faded. Over the past three decades, billions of funds have been invested in to researching and understanding the causes of autism spectrum disorders. However, research to date has not produced a single causal link but built a complex picture of associated biological, environmental and neurological causal factors. What has been confirmed through empirical research is that there are a number of genetic variations in individuals with autism (Abrahams and Geschwind, 2008), and neurological differences in how the brain develops (Courchesne, Carper at al. 2003).
It is also important to note that our general understanding of the brain and how it works is still limited. It is therefore somewhat naïve to assume that the neurological difference reported is as simple as typical (non-autistic) versus atypical (autistic). The range of individual difference can vary so much across the ‘autism spectrum’, that a well-known phrase best encapsulates this; ‘when you’ve met one person with autism, then you’ve met one person with autism’. There is such a variety of inter-connecting variables from genetics, cognition, environment, personality and other factors that carrying out research into causes has proven challenging.
There is no blood test, brain scan or any other objective test that can diagnose autism. Clinicians rely on observations of a person’s behaviour and a developmental history to make a diagnosis. In the US, UK, Australia, Singapore and much of the western world, the criteria for diagnosing autism are laid out in the Diagnostic and Statistical Manual of Mental Disorders (DSM) or International Statistical Classification of Diseases and Related Health Problems (ICD). The core criteria are problems with social communication and interactions, and restricted interests or repetitive behaviours. Both of these ‘core’ features must be present in early development.
The Centers for Disease Control and Prevention (CDC) estimates that 1 in 68 children in the U.S. have autism, which is likely to be similar worldwide. The prevalence is 1 in 42 for boys and 1 in 189 for girls. This estimate of autism prevalence is up 30 percent from the 1 in 88 reported in 2008, and more than double the 1 in 150 rate in 2000. In fact, the trend has been steeply upward since the early 1990s, not only in the U.S. but globally.
So why have numbers increased?
Autism didn’t make its debut in the DSM until 1980. In 1987, a new edition expanded the criteria by allowing a diagnosis even if symptoms became apparent after 30 months of age. In 1994, the fourth edition of the DSM broadened the definition of autism even further, by including Asperger Syndrome on the milder end of the spectrum. The current version of the
DSM (5th edition) was released in 2013, and collapsed autism, Asperger syndrome and pervasive developmental disorder-not otherwise specified (PDD-NOS) into a single diagnosis. These amendments are in line with an increased understanding of autism. Prevalence studies of autism in the past have not included those diagnosed with PDD-NOS and Asperger Syndrome, therefore this will have an impact on future figures using DSM-V criteria. It should also be noted that it is becoming increasingly recognised that women and girls are hugely under-represented; as diagnostic tools have been developed around male studies. It is believed that the ratio of 1:4 (girl to boy) ratio is likely inaccurate, and recognition and diagnosis in the female population is increasing. In addition to changes in diagnostic criteria, inclusion criteria and terminology of prevalence studies account for the variation in figures reported between studies and countries.
Increased awareness of knowledge of autism among paediatricians, psychologist, teachers and other professionals, alongside more accurate diagnostic tools has contributed to growing earlier recognition and diagnosis. Subsequently there has been a decrease in diagnosis of intellectual disability since the 1990s. In the US and UK during the 1990s, inclusion of ‘autism’ in Special Educational Needs codes of practice lead to an increase in diagnosis, as this meant more access to resources and support for these children. Currently variation in diagnosis between US states and UK local councils vary, depending on how local governments allocate funding to children with additional needs.
Biological factors may also contribute, for example, having older parents increases the risk of autism. Due to changes in societal norms, many couples are now older when they start a family. Children born prematurely also are at increased risk of autism, and more premature infants survive now than ever before.
Is there no real increase in autism rates, then?
Tracking back to ascertain whether there has been a rise in numbers is near impossible.
Awareness and changing criteria probably account for the bulk of the rise in prevalence. Steve Silberman in his book ‘Neurotribes’ provides the most accurate examination of this reported ‘epidemic’ to date. He surmises that although numbers appear to have increased, it is more likely due to changes in our recognition, diagnostic tools, support and inclusive practices, genetics and societal views has shifted widely over the years.
Dr Jennifer Greene
BSc (HONS), DEdChPsy, CPsychol
Consultant Educational & Child Psychologist
Abrahams B.S., Geschwind D.H. (2008) Advances in autism genetics: on the threshold of a new neurobiology. Nat Rev Genet, May; 9(5): 341-55
Courchesne, E., Carper, R. & Akshoomoff, N. (2003) Evidence of brain overgrowth in the First Year of Life in Autism. Journal of American medical Association, Vol290, no.3
Jaarsma P, Welin S (2011) Autism as a Natural Human Variation: Reflections on the Claim of the Neurodiversity Movemnet. Health Care Anal. 20(1): 20–30