How common is autism?

Research has been published in today’s Lancet on the prevalence of autism spectrum disorders (ASDs) in the population of UK children, suggesting that these disorders are more common than previously thought.

The paper reported that the prevalence of ASDs in the population is 116·1 per 10,000 of the population Рmeaning just over 1% of the population are likely to qualify for one of these diagnoses.

“One of these diagnoses” is the crucial phrase here, as Baird and colleagues were not looking just for ‘classic’ or ‘narrowly defined’ autism (diagnosed as childhood autism in the ICD-10), but at the whole of the autism spectrum disorders – also known as pervasive developmental disorders.

BBC News has a good write-up on the study including a crucial quote from the Lancet article’s main author Professor Gillian Baird:

Whether the increase is due to better ascertainment, broadening diagnostic criteria, or increased incidence is unclear.

In fact, the reported prevalence of the narrow form of autism was only 38.9 in 10,000 of the population, less than 0.4%.

In contrast, autism spectrum or pervasive developmental disorders have a much broader scope, and can include both a 10 year-old child with no language, severe learning disabilities, lack of social interest and restricted interests (‘narrow’ autism) to a bright articulate 10 year-old child who is socially awkward and bit inflexible in his thinking.

This is largely because of fairly recently included diagnoses such as ‘Asperger syndrome’, ‘Pervasive Developmental Disorder – Not Otherwise Specificed’ (PDD-NOS) and ‘Atypical Autism’ which, particularly for the latter two, have much wider criteria.

Although Baird and colleagues used systematic methods for making their diagnoses, it’s interesting that there’s quite a pressure on everyday clinicians to make these sort of diagnoses for children who are having emotional or behavioural problems.

Having one of these diagnoses entitles children to special educational support or even a place in an expensive yet well-supported special school in many areas of the UK.

Who wouldn’t want special support for their child who is doing badly in education and is constantly distressed by school life? This in turn puts pressure on local clinicians, and on the medical establishment, to recognise these difficulties by widening the diagnostic criteria.

I sometimes smile to myself when I see news stories about science and medicine being out of touch with society, since the history of medicine suggests that there is an intimate connection between medical decisions and social needs.

Link to abstract of Lancet study on ASD prevalence.
Link to BBC News story on research.