by Emma Walker

Created on: September 28, 2010

Autism is a lifelong developmental disability that affects the way a person communicates and relates to people around them.

The exact cause/causes of autism are not known although research suggests that multiple factors including genetics and environmental factors may be involved.

Genetic Factors of Autism

There is strong evidence that autism is influenced by genetics. If one child in a family has autism the risk that a younger sibling will also have autism has been estimated at ~4.5 %, and twin studies have found 60-80% concordance in identical twins and 10% in non identical (Dougherty 2002, E, Cook 1998, Bailey et al 1995, Gillberg & Coleman 2000).

Genetic research so far suggests that multiple genes may be involved in autism, with abnormalities in chromosome 15 including deletions, duplications, mutations and inversion being the most consistently found common fault in autistic individuals so far. Chromosome 15 has also been linked to some other medical conditions such as Angelmans Syndrome and Prader Willi Syndrome.

Chromosome 7 is another chromosome that has been identified as a potential candidate in autism (M, Chez et al 2000).

It is known that changes in the number or structure of chromosome 7 can cause speech, growth and developmental delays all of which have associations with autism.

The prevalence of autism in males is significantly higher than in females ~ 4:1, one theory that may help explain this is that one of the genes involved may be on the X chromosome, however autism is not purely an X-linked syndrome as evidence of male to male transmission has been seen.

Non-Genetic Factors of Autism

 There have been several non-genetic factors suggested as possible causes of autism including a’ typical brain development with possible involvement of the amygdala (an area of the brain that is thought to be important  in social development), environmental toxins, vitamin deficiencies and food allergies.

Currently it appears as if finding a single cause of autism is unlikely and that multiple factors are involved including genetic and non-genetic factors.

Hopefully one day in the not to distant future through on-going research, a definitive answer to the cause of autism may be found.

Reference/ further reading:

Bailey et al.1995 ‘Autism as a strongly genetic disorder: evidence from a British twin study’. Psychological Medicine; 25(1): 63-77.

Bertrand, J et al. 2001 ‘Prevalence of Autism in a United States Population: The Brick Township, New Jersey, Investigation’. Pediatrics; 108 (5): 1155-1161

Chez M, et al. 2000 ‘Secretin and autism: a two-part clinical investigation’. Journal of Autism and Developmental Disorders ;30(2):87-94 

Cook, E et al. 1998 ‘Linkage-Disequilibrium Mapping of Autistic Disorder, with 15q11-13 Markers’. American Journal of Genetics; 62 (5): 1077-1083

Gillberg, C & M, Coleman,2000. The Biology of the Autistic Syndromes. Mac Keith Pres. London.

 Wing,L and Potter,D (2002) The epidemiology of autistic spectrum disorders: is the prevalence rising? Mental Retardation and Developmental Disabilites, Research Reviews,8,(3) 151- 161

www.autism.org

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