In Denmark, the prevalence of children diagnosed with autism spectrum disorders has increased by almost two thirds in the past 20 years. A study published in the journal JAMA Pediatrics, found that it was due to a better quality of diagnostics, and not an ‘actual’ increase of the number of affected children. Although the term ‘autism’ has existed for more than a century, it was almost unknown before 1940s. For some 20 years after that, it was associated with schizophrenia and other mental diseases.

Expanding diagnostic criteria

Awareness of a need of adequate diagnostic tests increased with increasing knowledge about autism. It has led to an increase of the number of newly diagnosed patients. In Denmark, diagnostic criteria were expanded in 1994. These include a spectrum of disorders of both complementary and various sympthomatology, which expanded the primary definition of autism. In the course of 1995, the Danish programme of autism follow-up included not only those who were hospitalized (which was obligatory for children with autism at that time), but also those who were followed-up and in therapy in primary health care.

Since in Denmark every person has a health record and case history in the network system, it is easy for researches to conduct their studies because they have not been exposed to errors in designing them. A review of health records of all children who were born in Denmark from 1980 to 1991 – which is almost 668,000 children – has found that the increase of 60% in the prevalence of diagnosed autism was ascribed to that study.

The change of diagnostic criteria increased the number of the newly diagnosed by one third, and of those diagnose in primary health care by 42%. The big data base with around 500,000 children during a period of 10 years is what makes this study especially significant. Researchers and authors have had an amazing data base, which is rarely possible anywhere in the world, and their results have an impact on a series of further research, said Glen Elliott, medical director of Childrens Health Council in Palo Alto, California. However, there are still some questions unanswered, e.g., why Denmark still has a low prevalence of autism (54 per 10,000 children) which is much lower than in the USA (147 per 10,000 children). The question remains as to whether a level of awareness engaged in diagnostic autism spectrum disorders in these two populations produced the difference.

The definition of autism has dramatically changed since 1980 when it first appeared in DSM-III as ‘infantile autism’, and this diagnosis was established only if the child was younger than three years of age. In the revised DSM-5, explicit inclusive criterion to establish this diagnosis is neither that young age, nor the child’s language development. Most of the individuals with such diagnosis today would have not been diagnosed with autism following the criteria from 1980, where a clear differentiation between this diagnosis and schizophrenia did not exist.

Better diagnostics – more diagnosed children

Even high quality diagnosing is still a challenge for clinicians today, due to a very wide spectrum of symptoms. That is why there is that idea of increased prevalence of autism, which reflects changes in diagnostic criteria, and not the real changes in the prevalence of this neuro-developmental disorder. One study from 2013 describes grouping of a significantly higher prevalence in regions where conditions for professional diagnosis and treatment where better. In other words, the number of newly diagnosed cases increases with a better and more efficient diagnosing of this disorder.

However, that fact has often been ignored by a significant number of those who are into pseudo-scientific framework of the autistic spectrum disorder. Therefore we are encountering ignorance about the reasons why autism is not equally prevalent in the USA and in other countries. The reason for that is better availability of diagnostic procedures in the USA, awareness raising and better problem identification. For example, study conducted in South Korea in 2011 finds a prevalence higher than in the USA (2.6%, or around 1:38).

Objectively speaking, all the above does not conclusively reduce the possibility that there is an upward trend and a certain increase of prevalence. Can we explain the ‘majority’ of the increase by changes in diagnostic criteria and availability of health care? Moreover, that ‘majority’ is still only 60% and the rest of the increase, which is 40% remains unexplained.

Therefore, if there is an increase, can we think of how it can be explained? What we know for sure, it is not the vaccines. A small portion of the increase can be attributed to the increase of the average age of parents. Both women and men become parents later than ever in the history of humanity, and autistic spectrum disorders are related to parents’, especially fathers’ age. There is certainly an abundance of pseudo-scientific and alarming possible risks, none of which has been confirmed by scientific research. Since nobody has provided a plausible explanation for the increased prevalence of diagnosed autistic spectrum disorder, scientists are still researching…

Written by: Vanja Slijepčević Saftić, MD, Sc.D., paediatrician, subspecialist in child neurology

Other texts by the same author:

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