Genetics

Please explore our risk factor pages to learn more about the genetics of Autism Spectrum Disorder.


Genetics play a strong role in the development of Autism Spectrum Disorders (ASDs). Autism is shared among 50-70% of identical (monozygotic) twins, compared with 0-10% of fraternal twins1,2,3. Moreover, 1-6% of children diagnosed with autism also have a sibling who is diagnosed with autism, a much higher rate than the general population4.

Further evidence for a genetic risk for autism comes from well-defined genetic disorders such as Fragile X syndrome, where a significant proportion of affected individuals develop autism5. Autism in these cases is known as syndromic autism due to its link with a particular syndrome.

Key Points
  • Twin- and family-based studies show that autism is highly heritable.
  • Autism affects predominantly males, with an estimated male to female ratio of 4:1.
  • Autism is known as a complex genetic disorder since many different underlying genetic defects can cause the disorder.
  • Some of the genetic risk factors associated with autism include: rare single gene mutations, common variants in susceptibility genes, and chromosomal abnormalities such as copy number variations (CNVs; see below).
Misconception
  • Autism is caused by mutations in only one gene.

Fact
  • ASD is thought to be caused by a combination of genetic and environmental factors. To date, variations in almost 300 genes have been associated with Autism Spectrum Disorders, and these explain less than 10% of individuals with autism.

Read about other misconceptions.




References:
  1. Bailey A, Le Couteur A, Gottesman I, Bolton P, Simonoff E, Yuzda E, Rutter M. (1995) Autism as a strongly genetic disorder: evidence from a British twin study. Psychol Med 25(1):63-77. PMID: 7792363.
  2. Le Couteur A, Bailey A, Goode S, Pickles A, Robertson S, Gottesman I, Rutter M. (1996) A broader phenotype of autism: the clinical spectrum in twins. J Child Psychol Psychiatry 37(7):785-801. PMID: 8923222.
  3. Folstein SE, Rosen-Sheidley B (2001) Genetics of autism: complex aetiology for a heterogeneous disorder. Nat Rev Genet 2(12):943-55. PMID: 11733747.
  4. Chakrabarti S, Fombonne E (2001) Pervasive developmental disorders in preschool children. JAMA 285(24):3093-9. PMID: 11427137.
  5. Rogers SJ, Wehner EA, Hagerman R (2001) The Behavioral Phenotype in Fragile X: Symptoms of Autism in Very Young Children with Fragile X Syndrome, Idiopathic Autism, and other Developmental Disorders. Jour of Dev & Beh Ped 22(6):409-17. PMID: 11773805.