Genetics of Autism

Autism is mostly genetic, with a few environmental influences acting in the womb.
A study of over 2 million people that included over 14,000 autistic children estimated autism to be 83% genetic.Sandin S, Lichtenstein P, Kuja-Halkola R, Hultman C, Larsson H, Reichenberg A. The Heritability of Autism Spectrum Disorder. JAMA. 2017;318(12):1182–1184. doi:10.1001/jama.2017.12141 Past estimates ranged from 37% to >90%, based on twin concordance rates.American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Washington, DC. https://doi.org/10.1176/appi.books.9780890425596
== Genetics ==
Autism has a strong genetic basis.This Is How Much of Autism Is Genetic Researchers have associated many genes with autism, but it is not yet fully understood.
Approximately 15% of autistic people are associated with a known genetic variations, with different de novo copy number variants or de novo mutations in certain genes related to the disorder in different families. However, it doesn't seem to be completely penetrant even when autism is linked to a known genetic variation. The remaining cases seem to be polygenic, with possibly hundreds of genetic loci creating small contributions. 
== History ==
In 1977, Professor Michael Rutter and Dr. Susan Folstein completed the first systematic study of autistic twins.Feinstein, A. (2010). A history of autism: Conversations with the Pioneers. Wiley-Blackwell.1977 paper on the First Autism Twin Study. 1977 paper on the first autism twin study. Retrieved December 6, 2021, from https://web.archive.org/web/20150321221005/http://sfari.org/news-and-opinion/classic-paper-reviews/2008/1977-paper-on-the-first-autism-twin-study-commentary-by-angelica-ronald-and-robert-plomin. They showed in their study of 21 British twins that there was a high genetic component in autism.Folstein, S. & Rutter, M. (1977). Infantile autism: A genetic study of 21 twin pairs. Journal of Child Psychology and Psychiatry, 18, 297-321. For 10 pairs of fraternal (dizygotic) twins in which at least one of the twins was diagnosed with autism, none of the single co-twins was diagnosed with autism: concordance was zero for fraternal twin pairs. Heritable conditions were expected to run in families, which is why the possibility of the influence of genetics for autism was not researched. For the 11 pairs of identical (monozygotic) twins that were genetically identical, four of the 11 pairs were concordant for an autism diagnosis. The concordance for cognitive abnormalities was 82% in identical twins and 10% in fraternal twins. The difference in concordance for autism and concordance for cognitive disorder between identical and fraternal twins shows the importance of genetic factors in the etiology of autism. This was one of the first studies that led to a shift of autism being thought of as an environmentally-caused condition to being a heritable condition.
Autism is highly genetically heterogeneous and could be caused by both de novo and inheritable gene variations.Rylaarsdam, L., & Guemez-Gamboa, A. (2019, August 20). Genetic causes and modifiers of autism spectrum disorder. Frontiers. Retrieved December 6, 2021, from https://www.frontiersin.org/articles/10.3389/fncel.2019.00385/full. Research has shown that the genetic influence on autism is not due to one gene but might be due to many genes of small effect size. Within the past decade, hundreds of genes have been recognized that contribute to the differences in social cognition, communication, and behavior that autistic people experience. However, these only make up 10-20% of autism cases. Individuals with similar genetic variants may still have highly different needs.
== Environmental factors ==
Environmental factors most likely acting through epigenetic regulation may account for non-genetic factors. Many factors have been proposed.
All known teratogens (agents that affect fetal development) related to autism appear to act during the first eight weeks from conception.Arndt, T.L., Stodgell, C.J. and Rodier, P.M. (2005), The teratology of autism. International Journal of Developmental Neuroscience, 23: 189-199. https://doi.org/10.1016/j.ijdevneu.2004.11.001 Evidence suggests that autism begins in the womb.Autism begins in the womb, according to a new study Research suggests that exposure to pollution may increase the chance of autism.
Parents may first notice signs of autism around the time for routine vaccinations. This has sparked numerous mythsDoja A, Roberts W. Immunizations and Autism: A Review of the Literature. Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques. 2006;33(4):341-346. doi:10.1017/S031716710000528X
*Gerber JS, Offit PA. Vaccines and autism: a tale of shifting hypotheses. Clin Infect Dis. 2009 Feb 15;48(4):456-61. doi: 10.1086/596476. PMID: 19128068; PMCID: PMC2908388.Gross L. A broken trust: lessons from the vaccine--autism wars. PLoS Biol. 2009 May 26;7(5):e1000114. doi: 10.1371/journal.pbio.1000114. Epub 2009 May 26. PMID: 19478850; PMCID: PMC2682483. that have led to disease outbreaks, profiteering scams, and preventable deaths in children.Measles outbreak in Dublin, 2000 Researchers have exhaustedly proven that vaccines are not linked to autism, yet misinformation continues.Vaccines are not associated with autism: An evidence-based meta-analysis of case-control and cohort studiesDo Vaccines Cause Autism?Autism and VaccinesKnopf A. Time to remember: Vaccines don't cause autism. The Brown University Child and Adolescent Behavior Letter. 2021 Jul;37(7):9–10. doi: 10.1002/cbl.30559. Epub 2021 Jun 7. PMCID: PMC8207024.Link between autism and vaccination debunkedVaccines Don't Cause Autism (and Here's the Proof) Some people have pointed out that having an autistic child is better than having a medically at-risk child who is permanently damaged or killed by vaccine-preventable diseases.
== References ==
Category:Autism
Category:1970s
Category:Genetics