What is the role of genetics in the etiology of autism spectrum disorder (ASD)?

Updated: Sep 30, 2019
  • Author: James Robert Brasic, MD, MPH; Chief Editor: Caroly Pataki, MD  more...
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Familial factors influence the risk for autism spectrum disorders. The rate of autism spectrum disorder in children born into families that already have a child with an autism spectrum disorder is as high as 18.7 %, and the risk is twice as high in children born to families with 2 or more children with an autism spectrum disorder. [63] Girls born to a family that has a child with an autism spectrum disorder have 2.8 times the risk of having such a disorder. [63]

Twin studies have demonstrated a moderate degree of genetic heritability for autism and autism spectrum disorders, [64, 65, 66] with environment making a substantial contribution to the development of these conditions in the study subjects. [66]

Multiple family studies have suggested genetic components in many cases of autism. [67, 56, 68] For example, some asymptomatic first-degree relatives of some probands with autism have abnormalities in serotonin and other chemicals similar to the probands.

Finding genetic bases for autism is a promising research goal. Factor analysis of datasets from the Autism Genome Project has suggested linkage of a joint attention factor with 11q23 and of a repetitive sensory-motor behavior factor with 19q13. [69] However, the clinical usefulness of the assessment of families of individuals with autism has not been established.

While a third of monozygotic twins are concordant for autism, dizygotic twins are concordant for autism at rates of 4-8%, [70] which is comparable to siblings. A focused neurogenetic evaluation of children with autism spectrum disorder yields a genetic disorder in two fifths of the children. [71] For example, mutations in the gene SHANK3 are associated with autism spectrum disorders. [72, 73]

Fragile X syndrome, a condition associated with autism, can be identified through genetic testing. [74] Antagonists to metabotropic glutamate receptors can reverse the symptoms in mouse models of fragile X syndrome. [75] Autism has also been associated with tuberous sclerosis, a disorder with specific genetic mutations. [76, 77]

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