NOTES ON THE EPIDEMIOLOGY OF
AUTISTIC DISORDER
and
ASPERGER SYNDROME
with regard to
ADULTS IN WORCESTERSHIRE
1 Aim
The aim of these Notes is to estimate the number of adults having Autistic Disorder or Asperger Syndrome in Worcestershire, for the further purpose of planning appropriate services for their needs from April 2007. These Notes were requested by Worcestershire National Health Service Mental Health Primary Care Trust and by Worcestershire Social Services Directorate.
2 Conclusion
It is likely that in 2007 Worcestershire will have in excess of 700 adults with Autistic Disorder.
In addition there are likely to be between 500 and 900 adults with Asperger Syndrome.
These adults are not included in the definitions of mental illness and learning disability as currently covered by Worcestershire statutory services.
The further purpose of the Worcestershire National Health Service Mental Health Primary Care Trust and Worcestershire Social Services Directorate is to plan for meeting their needs. This purpose requires fiscal and tactical commitment and planning forthwith, so as to provide for appropriate resources by April 2007. These resources should address: -
• residential needs
• support needs in the work place
• social service
• clinical service including professional education.
3 Preamble
The broad category of ‘Pervasive Developmental Disorders' * includes ‘Autistic Disorder' and ‘Asperger Syndrome'. These are both ‘Autistic Spectrum Disorders' (sometimes known as the ‘autistic continuum').
Neither Autistic Disorder nor Asperger Syndrome are considered a mental illness, nor are they classed as learning disabilities. They are bio-neurological disorders which affect the functioning of the brain and cause lifelong developmental disability.
Because the different conditions have shared and varying features, confusion of category and analysis often occurs.
* The other Pervasive Developmental Disorders are Rett's Disorder, Childhood Disintegrative Disorder and Pervasive Developmental Disorders Not Otherwise Specified.
4 Definitions
Royal College of Psychiatrists' definition: -
“Autism is a disorder which usually appears within the first three years of life and may result in learning difficulties, speech problems and difficulty relating to people. ”
‘Autism' is characterised by a ‘triad of impairments' (Wing and Gould, 1979) namely: -
• Difficulties forming social relationships
• Problems with verbal and non-verbal communications
• Development of strong narrow obsessional interests.
‘Kanner Syndrome' (Dr Leo Kanner, 1943) is autism as he observed it in early infantile years.
‘High Functioning Autism' is loosely defined either as an autistic condition concurrent with average or high intelligence (this relates to the definition of Learning Disability, being IQ <70), or as a version of autism in which the symptoms are mild and allow a degree of social functioning. Some people believe it synonymous with Asperger Syndrome.
Royal College of Psychiatrists' definition: -
“Asperger's syndrome is a genetic disorder thought to be on the same spectrum as Autism. People with Asperger's syndrome have difficulties in three main areas: socialising, communication and behaviour. ”
World Health Organisation ICD 10 definition: -
“Asperger's syndrome: a disorder of uncertain nosological validity, characterised by the same type of qualitative abnormalities of reciprocal social interaction that typify autism, together with a restricted, stereotyped, repetitive repertoire of interests and activities. It differs from autism primarily in the fact that there is no general delay or retardation in language or in cognitive development. This disorder is often associated with marked clumsiness. There is a strong tendency for the abnormalities to persist into adolescence and adult life. Psychotic episodes occasionally occur in early adult life.”
‘Asperger syndrome' (named by Lorna Wing in 1980, after Dr Hans Asperger's observations in 1944) is a condition within the Autistic Spectrum Disorder. It is considered technically not to exist concurrent with a learning disability. It includes the ‘triad of impairments' but is often differentiated from high-functioning autism, with AS considered as featuring: -
• ‘Milder' symptoms
• Near-normal childhood speech development
• A desire to form friendships.
Some people differentiate Asperger's from Autistic Disorder by referring to the latter as ‘classic autism'.
‘Syndrome' (Greek sundroma ‘running together') means a group of signs and symptoms that together are characteristic or indicative of a specific disease or other disorder.
‘Adults' for the purpose of these Notes, are deemed those 16 years or over.
Note on abbreviations: -
PDD Pervasive Developmental Disorder
AS Asperger Syndrome
ASD Autistic Spectrum Disorder
KS Kanner Syndrome
5 Methodology
No original research has been conducted, in compiling these Notes.
Documents regarding Autism and Asperger Syndrome have been obtained chiefly from the Internet. Their content has been read and the figures summarised.
The different figures are expressed uniformly on a procentual basis (rather than per 10,000, per 1000, per population or by integer, as used by different researchers).
For the following reasons, the figures are extremely difficult to present on an equivalent basis: -
• samples overlap and conflict; for example Kanner Syndrome appears sometimes to be used as a simile for Autistic Disorder or Autism
• groupings are subject to the authors' definition of the conditions; for example Asperger Syndrome is sometimes but not always identified as being the same as High Functioning Autism
• some writers use the term ‘autism' and do not clarify whether they are referring to Autistic Disorder or Autistic Spectrum Disorder.
Figures for the population of Worcestershire have been obtained from the Internet using the local Government website.
6 Commentary on figures
Autistic disorder
The median figure is 0.26%. The modal area is 0.17%.
Among the lowest figures 0.045% is that assessed in England 39 years ago. The highest (0.9%) is claimed by a rights-to-benefit campaigner in 2005.
Six of the figures, of which five are the highest, appear to account for Autistic Spectrum Disorder rather than Autistic Disorder and thus may include Asperger Syndrome.
The figure of 0.168% offered by Professor Fombonne appears robust in that it is based on a demographically significant sample and took place over a period of 4 years. It is also close to the mode. It is limited to children as are all the other surveys covered in these Notes.
We propose that the figure 0.168% be used as likely minimum prevalence of autism.
Asperger Syndrome
The median figure is 0.24%. The modal area is 0.1% given that that the three Swedish figures probably come from the same source.
The lowest figure (0.01%) comes from the 39 year old British estimate. The low 0.084% is based on a pre-school sample and probably reflects the difficulty in diagnosing Aspergers in most children.
Again it is the study in Staffordshire by Professor Fombonne of McGill University, which appears the most convincing, with the recent figure of 0.11%. The sample bases are however exclusively children and very many, probably the majority of AS cases are first diagnosed in adulthood. It is also felt that there is poor recognition of AS in females due to their ability to ‘hide' the problem for longer (better social skills).
Professor Simon Baron-Cohen of the Autism Research Centre at Cambridge University has written to say that there is no epidemiological data on the rates of AS in adulthood. Diagnostic facilities are of poor availability.
We propose that Professor Fombonne's figure 0.11 % be used as likely minimum prevalence of Asperger Syndrome with a possible higher figure of 0.2% .
Population
Worcestershire County Council's forecast of total population in the County for 2007 is 558,400. Up to age 19 the population is forecast at 132,300. Assuming equal distribution of ages 15-19, the population aged 16 years and over (‘adults' for the purpose of this survey) would be 433,240 .
The County's population study by gender, on the same basis, forecasts a 2007 population æt. 16 + of male 221,300; female 211,940.
Prevalence of Autistic Disorder by gender
Our study has not found any analysis of the prevalence of Autistic Disorder by gender.
Prevalence of Asperger Syndrome by gender
Dr Ian Newey quotes Gillberg (1989) estimating that the male to female ratio is 10:1 based on clinical experience.
The World Health Organisation ICD-10 classification gives the male to female ratio as 8:1.
Woolf and Barlow (1979) give a male to female ratio of 9:1.
Dr Lorna Wing cites her clinical experience as 6 girls to 28 boys - 4.66:1.
We adjudge the likely figure to be male to female ratio 8:1 .
7 Application of figures
Autistic disorder
On the basis of the above assessments the population of Worcestershire in 2007 aged 16 and over with autistic disorder is likely to be 728.
Asperger syndrome
On the basis of the above assessments the population of Worcestershire in 2007 aged 16 and over with Asperger syndrome is likely to be a minimum of 476 of which 416 males. An alternative, higher figure of 866 (758 males) may be forecast.
If you wish to see the detailed tables and statistics upon which these Notes are based, please email us your address.
Lawrence Brewer
Secretary, WaASP
21 November 2005
www.WaASP.org
info@WaASP.org
