Although commonly associated with general intellectual disabilities - approximately 75% of people with autism have a non-verbal Intelligence Quotient (IQ) below 70 - autism can also occur in individuals of normal, or even superior intelligence.

Patricia Howlin (UK)

Although commonly associated with general intellectual disabilities - approximately 75% of people with autism have a non-verbal Intelligence Quotient (IQ) below 70 - autism can also occur in individuals of normal, or even superior intelligence. Because of the nature of the disorder (age of onset is not necessarily the same as age of diagnosis) true incidence is difficult to determine. Prevalence studies however suggest that a conservative estimate is around 20-30 per 10,000 if the wider spectrum is included. Although prevalence estimates have increased steadily over recent years, there is no strong evidence to suggest a real rise in incidence. Instead the rise is probably due to better recognition of the condition. In common with many disorders associated with communication problems, the male to female ratio is about 4:1.

Diagnostic Criteria
Diagnosis is based on three main criteria, with social and communication difficulties being evident within the first 3 years of life. Diagnosis requires a detailed developmental history as well as a careful current state examination. It is also important to obtain accurate assessments of intellectual and linguistic functioning. Individuals with "Asperger Syndrome" share similar impairments in reciprocal social and communication skills and obsessional interests, but are of normal I.Q. and do not show early language delays.

Diagnostic CriteriaMain characteristics
Abnormal Social DevelopmentProblems in developing reciprocal social relationships; lack of shared attention; impaired empathy; failure to understand social "rules"; inability to relate to peers; unusual eye-contact and facial expression
Communication Deficits

About 50% fail to develop useful speech. In the remainder, language development is delayed, except for Asperger's syndrome, in which first words/phrases develop at normal age.

Expressive language is characterised by: repetition; delayed echolalia; stereotyped utterances; lack of reciprocal conversation or "chat"; pronoun reversal & neologisms; abnormalities in rhythm and pitch; abnormal use of gesture. Internal language (the capacity for pretend or imaginative play) is also affected.

Comprehension is limited and very literal; understanding of abstract concepts is particularly impaired.

Restricted and Repetitive
Interests and Behaviour

Stereotyped and repetitive play patterns; collecting and lining up of particular objects; fascination with/attachments to unusual objects; pre-occupations with particular topics; resistance to change; insistence on routines; stereotyped movements.

All people with autistim have difficulties in each of the three main areas, although the manifestation of problems will be affected by intellectual level and, to some extent, age. Individuals of higher intelligence are more likely to develop speech, show greater interest in social interactions, and tend to be preoccupied with special interests, or collecting "facts" rather than objects.

Prognosis and Treatment
Autism is a developmental disorder, and although many people show improvements with age, the fundamental problems persist throughout life. The majority of adults remains heavily dependent on their families or require specialist accommodation and support, although some more able individuals do achieve social independence. Despite occasional claims to the contrary, there are no cures and the effects of pharmacological or dietary treatments are limited or inconsistent. The best prognosis occurs in individuals of higher intellectual ability, who have developed useful speech by the age of five to six years. Later behavioural difficulties often result from the children's inability to use or understand language effectively, from their resistance to changes in routine, or from their ritualistic and obsessional behaviours. Early intervention for families, and appropriate educational placement can do much to modify the impact of these problems, which, if not dealt with effectively, may become very persistent and pervasive and can greatly disrupt family life. Medication can be helpful if additional problems, such as epilepsy, anxiety or depression occur as children grow older.

About 20-30% of children with autism develop epilepsy (usually in the early teens); neuro-imagining techniques reveal abnormalities in brain function in others. There are putative links with prenatal infections such as rubella, or with encephalitic illnesses. There is some association (though infrequent) with single gene disorders such as phenylketonuria, and possibly with chromosomal abnormalities such as Fragile X. However, the autistic "picture" in these cases tends to be atypical. The strongest link is between autism and tuberous sclerosis.

Twin and family studies indicate that the most common cause is likely to be genetic. There is an extremely high rate of concordance for autism in monozygotic twins (92%, compared with 10% of dyzygotes), and for families with one autistic child there is a genetic risk of about 3% of having another child with autism. Rates of milder but related problems, such as communication, cognitive and social problems in other family members, are significant, at around 20%. Although obstetric factors were once thought to be implicated, these now also seem to be related to genetic susceptibility. Genetic counselling is thus an important part of the assessment and treatment process for families. However, because the condition is likely to be genetically heterogeneous, identification of the particular genes involved presents many problems.

Differential Diagnosis
Autism can sometimes be confused with other conditions associated with language or cognitive impairments. Children with profound intellectual disabilities may show somewhat similar patterns of social, communication and behavioural problems. Severe receptive developmental language disorders may also share some features characteristic of autism. In autism, however, social and communication problems are out of keeping with general cognitive development, and whereas in language disorders, behaviours generally improve as language develops, this is often not the case in autism. Other genetic conditions, such as Fragile X, may have some superficial similarity, but do not fulfil all three diagnostic criteria.

Further reading

General Information
The National Autistic Society publishes a number of information leaflets and papers on Autism and Asperger Syndrome. The publication list can be obtained from the National Autistic Society, 393 City Road London EC1V 1NE. Further details can be found on their web-site:

Frith U, Autism and Asperger Syndrome. Cambridge University Press 1991: Explaining the enigma. Oxford Blackwell 1989. (Two highly readable and informative books on the problems associated with these conditions, in both adults and children).

Howlin, P. Treating children with Autism & Asperger Syndrome: A guide for carers and professionals. Chichester, Wiley. 1997.

Howlin, P. (1997) Autism - Preparing for Adulthood (Describe and evaluates practical approaches to intervention). London Routledge.

Lord C. & Bailey. Autism and pervasive developmental disorders in Rutter et al, Child and Adolescent Psychiatry. Modern Approaches. Oxford Blackwell Scientific Publications 2001.
(A useful and up-to-date summary of recent research in the area of autism).

Gillberg C & Coleman M. The biology of the autistic syndrome - 3rd edition, MacKeith Press, Oxford Blackwell 2001
(Deals with topics such as diagnosis, prevalence and prognosis and reviews literature related to genetic, biochemical, neuropathological and neuropsychological issues in autism).

Chakrabati, s & Fombonne, E (2001) Pervasive developmental disorders in pre-school children. Journal of American Medical Association, 285, 3093-3099

Baron-Cohen, S., Cox, A., Baird, G., Swettenham, J., Nightingale, N., Morgan, K., Drew, A. & Charman, T. (1996) Psychological markers in the detection of autism in infancy in a large population. British Journal of Psychiatry, 168, 158-16

Berument, S.K., Rutter, M., Lord, C., Pickles, A., and Bailey, A. (1999). Autism Screening Questionnaire:diagnostic validity. British Journal of Psychiatry, 175, 444-451

Lord, C. (1997) Diagnostic instruments in autistic spectrum disorders. In D. Cohen and F. Volkmar (Eds.), Handbook of Autism and Pervasive Developmental Disorders (2nd Edition, pp.460-483). New York: Wiley.

Szatmari, P. (1992). The validity of autistic spectrum disorders: a literature review. Journal of Autism and Developmental Disorders, 22 , 583-600.

Volkmar, F. and the Work Group on Quality Issues (1999) practice parameters for the assessment and treatment of children, adolescents, and adults with autism and other pervasive developmental disorders. Supplement to Journal of Academy of and Adolescent Psychiatry. 38, 32(s) to 54(s)

Wing L. (1993). The definition and prevalence of autism: a review. European Child and Adolescent Psychiatry, 2, 61-74.

For a more detailed article by this author see 'Autistic Spectrum Disorders'.

This article was first published on the site in 2002.