Genetics and Autism
Since autism was first described, it has been noticed that in some families more than one individual is diagnosed with autism. This suggests that there is a genetic component to autism. Other studies show that autism occurs more often in identical twins than non-identical twins than would be expected if genetic factors were not involved.
About 10 to 15 percent of individuals diagnosed with autistic disorder have an identifiable genetic condition:
In most cases of autism, no specific underlying cause can be determined. These cases of autism are called idiopathic autism. Evidence suggests that idiopathic autism results from a complex interaction of genetic and environmental factors. Twenty or more genes may play a role in the development of autism. Such genes, called susceptibility genes, predispose an individual to the development of autism. It is thought that in a specific individual, interplay between a subset of these genes and environmental factors lead to the development of autism.
Though no specific genes have been identified, research has found regions of various chromosomes that may have a gene associated with autism. These include regions on chromosome 2, 3, 7, 15, and X. Candidate genes for autism have been identified in several of these regions. A candidate gene is a gene that researchers think may be related to a particular disease or condition. More research is needed to identify additional candidate genes and to determine if already identified candidate genes actually play a role in the development of autism.
About 10 to 15 percent of individuals diagnosed with autistic disorder have an identifiable genetic condition:
- Chromosome abnormalities have been reported in individuals with autism.
- Approximately 2 to 3 percent of individuals with autism have Fragile X syndrome. Characteristics of Fragile X syndrome include mental impairment ranging from learning disabilities to mental retardation, attention deficit, hyperactivity, and specific physical features. Fragile X syndrome is caused by an abnormality in the FMR1 gene on the X chromosome.
- Approximately 0.4 to 2.9 percent of individuals with autism have Tuberous Sclerosis complex. Characteristics of Tuberous Sclerosis complex include lesions of the skin and central nervous system, benign tumors of various organs, and seizures. TSC is caused by abnormalities in one of two genes, TSC1 (found on chromosome 9) and TSC2 (found on chromosome 16).
In most cases of autism, no specific underlying cause can be determined. These cases of autism are called idiopathic autism. Evidence suggests that idiopathic autism results from a complex interaction of genetic and environmental factors. Twenty or more genes may play a role in the development of autism. Such genes, called susceptibility genes, predispose an individual to the development of autism. It is thought that in a specific individual, interplay between a subset of these genes and environmental factors lead to the development of autism.
Though no specific genes have been identified, research has found regions of various chromosomes that may have a gene associated with autism. These include regions on chromosome 2, 3, 7, 15, and X. Candidate genes for autism have been identified in several of these regions. A candidate gene is a gene that researchers think may be related to a particular disease or condition. More research is needed to identify additional candidate genes and to determine if already identified candidate genes actually play a role in the development of autism.