SSBP Information Sheet
AUTISM AND ASPERGER SYNDROME

Classification:
These are the best defined of the conditions included by DSM-IV & ICD-10 in the category of Pervasive Developmental Disorders (PDD). The others include atypical autism and PDD Not Otherwise Specified. Rett syndrome and Childhood Disintegrative Disorder are also incorporated within in the PDD category although they have very different causes and trajectories. There is continuing debate as to whether autism and Asperger syndrome are distinct conditions within the PDD Classification, or whether Asperger syndrome is synonymous with high functioning autism. Current research tends to support the latter view (Makintosh & Dissanayake, 2004)

First described:
Autism by Kanner in 1943; Asperger syndrome by Asperger in 1944. Both accounts note the abnormal patterns of communication and social development and the presence of ritualistic and stereotyped behaviours that are now recognised as the core symptoms of Autism Spectrum Disorders (ASD) (Lord & Bailey, 2002). Both men also described a variety of other behavioural difficulties and they included individuals of normal/above average IQ, as well as those with more severe cognitive impairments.

Aetiology:
There is no evidence that environmental factors (e.g. MMR or other vaccines) cause autism. The risk of autism in siblings of probands is significantly increased and there is an exceptionally high concordance rate in monozygotic twins. Family studies indicate that a “lesser variant” of the condition (i.e. problems related to social, language and/or cognitive functioning) occurs in up to 20% of first degree family members. Autism is not a single gene disorder and current evidence suggests that between 2 and 10 genes are probably involved. Possible candidate sites identified include chromosomes 2q, 7q and 16p (International Molecular Genetic Study of Autism Consortium 2001) but various other sites, including 13q and 15q have also been implicated.

Associated conditions:
There is a significant association between autism and Tuberous Sclerosis and a lesser association with Fragile X. Links with other conditions have also been described (e.g. rubella, cytomegalovirus, phenylketonuria) but the phenotype in these cases tends to be atypical. Epilepsy, often with onset in early teens, occurs in 20-30%.

Prevalence:
Estimates have risen steadily over time. A comprehensive review by Fombonne (2003) suggests a minimum estimate of around 1 per 1,000 for autism; with the figure for all PDD’s ranging from approximately 3 to 6 per 1,000.

Physical Phenotype:
This is usually normal although minor physical anomalies are not uncommon.

Life expectancy/natural history:
Life expectancy appears normal. Many individuals, especially those who are more able do show improvements with age. Outcome depends partly on innate factors, such as IQ, and partly on the adequacy of educational, occupational and other support systems (Howlin et al., 2004).

Behavioural and cognitive characteristics:
Autism and Asperger syndrome are identified by a “triad” of impairments: abnormal development of social skills and communication, and the presence of ritualistic and stereotyped behaviours/interests. Onset of language is usually significantly delayed in autism but by definition there are no marked delays in Asperger syndrome. Although frequently associated with cognitive delays, recent studies suggest that up to 70% of individuals with ASD may in fact be of normal intellectual ability. IQ in Asperger syndrome is, by definition, within the normal range (= 70). In children with autism non-verbal IQ is frequently higher than Verbal IQ, although this pattern may be reversed in older, more able individuals.

Outcome in adulthood is determined both by innate cognitive abilities and the levels of educational and post- school support provided. Mental health problems, especially related to anxiety and depression often emerge in late adolescence/ early adulthood.

References
Fombonne, E. (2003) Epidemiological surveys of autism and other pervasive developmental disorders. J Autism & Developmental Disorders, 33, 365-382

Howlin, P.,Goode, S.,Hutton J. Rutter M. (2004) Outcome in adults with autism. J. Child Psychology & Psychiatry.45, 212-229

International Molecular Genetic Study of Autism Consortium (IMGSAC) (2001) A Genome wide Screen for Autism: Strong Evidence for Linkage to Chromosome 2q, 7q, and 16p. American Journal of Human Genetics 69 570-581.

Mackintosh, K.E. & Dissanayake, C. (2004) The similarities and differences between autistic disorder and Asperger Disorder: A review of the empirical evidence. Journal of Child Psychology and Psychiatry 45. 421-434

Kanner, L (1973) Childhood Psychosis: Initial Studies and New Insights New York. Winston/Wiley

Lord, C. & Bailey, A. (2002) Autism Spectrum Disorders. In M Rutter & E Taylor (Eds) Child and Adolescent Psychiatry (4th Edition) pp 636-663. Oxford: Blackwell).
Wing, L (1981) Asperger’s syndrome: A clinical account. Psychological Medicine, 11, 115-129.

Patricia Howlin, August, 2005

www.nas.org.uk
www.autism-in-scotland.org.uk