Is Autism Genetic?

The autism spectrum is a developmental disorder that affects communication, social, verbal, and motor skills. Symptoms generally appear in early childhood, and since autism is a spectrum, this means that severity is widely varied. No two autistic people share the exact same symptoms. The American Autism Association states that 1 in 68 American children have some form of autism.
The exact cause of autism is unknown, but studies have shown the disorder is highly hereditary. In a study conducting identical twins, when one twin is autistic, the other twin is autistic 80% of the time, and 40% in fraternal twins. If a single baby is autistic, the chances of their younger sibling also being autistic are only 2-6%, but if a couple already has two autistic children, the chances of the third child being autistic rise to 35%.
There are several studies confirming that autism is in fact at least a partially genetic condition, as researchers have found there are roughly 65 genes strongly related to autism, and 200 genes that have weaker ties. However, no one single gene mutation guarantees autism, as patients in autism studies don’t all have the exact same mutations.
When it comes to genetic mutations, there are common variant mutations, which is a mutation that at least 1% of the population shares, and rare variant mutations, which less than 1% of the population shares, and usually these mutations have stronger effects. Autism is likely caused by many common variants and rare variants working together. Autism can be, and is usually diagnosed, in patients that have no family history of autism. This is called a de novo mutation, or a gene that appears for the first time in a family.
Mutations can be passed down from parents, but de novo mutations usually come from mutations in the ova, sperm, or fertilized ova. Mutations are likely caused by the environment, but it is unknown as to which environmental factors contribute to autism. Many researchers claim that complications at birth and poor maternal health can raise the risk of autism, but neither of these factors guarantee autism, and autism can also happen in a successful pregnancy and birth. Considering that parents don’t remember every aspect of their child’s gestation and birth, reports may be biased based on what the parents think is the explanation for their child’s autism.
A study conducted in 2014 suggest that genes may just be the beginning. This study observed that RNA-sequencing in the corpus callosum in autistic individuals showed extensive gene mis-expression, and that some of the genes that had been mutated affected oligodendrocyte development, which largely populated the corpus callosum. This suggests that genes themselves do not cause autism, but the mutated genes affect entire segments of brain development, which can lead to autism.
There are a few barriers to autism research. Many autistic individuals are unable to legally consent to studies, so genetic testing of severely autistic individuals is limited. Furthermore, autism is usually comorbid with other disorders such as Down’s syndrome, anxiety, and/or ADHD, which could also skew genetic testing. There is a chance that a person diagnosed as autistic has been misdiagnosed, as autism is very similar to a number of conditions, such as Rett syndrome, Fragile X, and Nonverbal Learning Disorder.
Interestingly, in a study comparing the genes of autistic patients to their non-autistic parents and siblings, a mother can have the genes consistent with autism but not have the disorder, but if her son inherits those same genes, he is affected. Does this imply that women need to have more mutated genes in order to be affected by autism? Does this also explain why there seem to be more autistic men than women? Does this mean the X-chromosome is affected by autism, as women have two but men only have one?

Works Cited:
American Autism Association. "What Is Autism?" Myautism.org. N.p., 2016. Web.

Deweerdt, Sarah. "Why Don't We Know What Environmental Factors Cause Autism?" Spectrum | Autism Research News. N.p., 26 July 2017. Web.

Li, J., M. Shi, Z. Ma, S. Zhao, G. Euskirchen, J. Ziskin, A. Urban, J. Hallmayer, and M. Snyder. "Integrated Systems Analysis Reveals a Molecular

Network Underlying Autism Spectrum Disorders." Molecular Systems Biology 10.12 (2014): 774. Web.

Tech Museum of Innovation. "Autism and Genetics." Genetics.thetech.org. Department of Genetics, Stanford School of Medicine, 2013. Web.

University of Washington Health Services/UW Medicine. "Family Genetics Study Reveals New Clues to Autism." ScienceDaily. ScienceDaily, 12 May 2015. Web.

Wright, Jessica. "Twin Study Unearths Clues to Role of Environment in Autism." Spectrum | Autism Research News. N.p., 09 Oct. 2015. Web.

Zeliadt, Nicholette. "Autism Genetics, Explained." Spectrum | Autism Research News. N.p., 30 June 2017. Web.