page_title: Autism spectrum
section_title: Genetics
hierarchical_section_title: Autism spectrum / Causes / Genetics
caption_attribution_description: English: Autism genes have similar downstream effects on brain development; This work 'Autism genes have similar downstream effects on brain development' uses a photo of Diagram of human brain by Hugh Guiney, used under CC BY. "Autism genes have similar downstream effects on brain development" is licensed under CC BY by Anwer2007 (talk) 09:11, 29 April 2020 (UTC)
context_page_description: The autism spectrum encompasses a range of neurodevelopmental conditions, including autism and Asperger syndrome, generally known as autism spectrum disorders. Individuals on the autistic spectrum experience difficulties with social communication and interaction and also exhibit restricted, repetitive patterns of behavior, interests, or activities. Symptoms are typically recognized between one and two years of age. Long-term problems may include difficulties in performing daily tasks, creating and keeping relationships, and maintaining a job.
  The cause of autism spectrum conditions is uncertain. Risk factors include having an older parent, a family history of autism, and certain genetic conditions. It is estimated that between 64% and 91% of risk is due to family history. Diagnosis is based on symptoms. In 2013, the Statistical Manual of Mental Disorders version 5 replaced the previous subgroups of autistic disorder, Asperger syndrome, pervasive developmental disorder not otherwise specified, and childhood disintegrative disorder with the single term "autism spectrum disorder".
context_section_description: As of 2018, it appeared that somewhere between 74% and 93% of ASD risk is heritable.  After an older child is diagnosed with ASD, 7–20% of subsequent children are likely to be as well. If parents have a child with ASD they have a 2% to 8% chance of having a second child with ASD. If the child with ASD is an identical twin the other will be affected 36 to 95 percent of the time. If they are fraternal twins the other will only be affected up to 31 percent of the time.
  As of 2018, understanding of genetic risk factors had shifted from a focus on a few alleles to an understanding that genetic involvement in ASD is probably diffuse, depending on a large number of variants, some of which are common and have a small effect, and some of which are rare and have a large effect. The most common gene disrupted with large effect rare variants appeared to be CHD8, but less than 0.5% of people with ASD have such a mutation.  Some ASD is associated with clearly genetic conditions, like fragile X syndrome; however only around 2% of people with ASD have fragile X.
  Current research suggests that genes that increase susceptibility to ASD are ones that control protein synthesis in neuronal cells in response to cell needs, activity and adhesion of neuronal cells, synapse formation and remodeling, and excitatory to inhibitory neurotransmitter balance. Therefore despite up to 1000 different genes thought to contribute to increased risk of ASD, all of them eventually affect normal neural development and connectivity between different functional areas of the brain in a similar manner that is characteristic of an ASD brain. Some of these genes are knows to modulate production of the GABA neurotransmitter which is the main inhibitory neurotransmitter in the nervous system. These GABA-related genes are underexpressed in an ASD brain. On the other hand, genes controlling expression of glial and immune cells in the brain e.g. astrocytes and microglia, respectively, are overexpressed which correlates with increased number of glial and immune cells found in postmortem ASD brains. Some genes under investigation in ASD pathophysiology are those that affect the mTOR signaling pathway which supports cell growth and survival.
  All these genetic variants contribute to the development of the autistic spectrum, however, it can not be guaranteed that they are determinants for the development.
caption: Hundreds of different genes are implicated in susceptibility to developing autism, most of which alter the brain structure in a similar way
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