Twin studies and gene mutation research suggests that autism is strongly genetic, but other factors, like gestational diabetes, can elevate autism risk.
Autism is a developmental condition that can interfere with a person’s ability to communicate with others and result in rigid behavior, such as being fixated on routines. According to research, genetics can strongly influence autism risk. In fact, experts report that autism is 50% due to genetic causes.
Does Autism Run in Families?
With research establishing that genetics are linked to autism, there is evidence that autism can run in families. For example, one study found that among families with identical twins, if one twin has autism spectrum disorder, the other twin was 153 times more likely to also have the disorder.
The following additional familiar autism risk levels were found:
- Fraternal twins: 8.2 times more likely
- Full siblings: 10.3 times more likely
- Maternal half-sibling: 3.3 times more likely
- Paternal half-sibling: 2.9 times more likely
- Cousins: 2 times more likely
This means, for example, that a person with a cousin with autism is twice as likely to have autism.
Studies on Twins and Autism
Scientists have extensively studied twins and autism risk. An analysis of multiple studies concerning twins and autism found that there is almost a perfect correlation between identical twins and autism, meaning that it is highly likely that a person will have autism if his or her identical twin is also diagnosed.
The study found a moderate correlation between fraternal twins and autism, suggesting that the risk is not as high as in identical twins. The authors of this analysis concluded that environmental factors that are shared between twins contribute to autism risk, but there are strong genetic effects on autism.
Additional Autism Risk Factors
While there is a strong link between genetics and autism, there are other factors aside from genes and family history that can increase autism risk. For example, there are prenatal risk factors for autism. A review of 40 studies shows that several prenatal factors can increase the risk of autism. These factors include having parents who are older at the time of birth, being born to a mother who uses medication during pregnancy, having a mother who had gestational diabetes, and being a firstborn child versus being the third or later child born to a mother.
Another analysis of the research found that all of the following can increase the risk of autism:
- Fetal distress
- Difficulties with umbilical cord
- Trauma or injury during birth
- Multiple birth (being a twin, triplet, etc)
- Mother experiencing hemorrhage
- Being born small for age or at a low birth weight
- Congenital defects
- Feeding difficulties
- Low Apgar scores
- Anemia after birth
- High bilirubin levels after birth
- Meconium aspiration during birth
Based on the findings in the research, it appears that factors that occur during pregnancy and during or immediately after birth can increase the risk of autism. It can be concluded that while genetics can contribute strongly to autism, there are other factors that can also elevate the risk.
Further Autism Genetics Research
In addition to research on risk factors, scientists have conducted further autism genetics research. They have found that multiple genes are linked to developmental disorders like autism, and there are 25 genes that are linked specifically to autism over other developmental disorders like intellectual disabilities.
The research also shows that there are genes uniquely associated with high functioning autism, which occurs in individuals with an IQ of over 100. These findings demonstrate that autism has strong genetic links.
National Institute of Mental Health. “Autism spectrum disorder.” March 2018. Accessed October 2, 2019.
Sandin, Sven; et al. “The familial risk of autism.” JAMA, May 7, 2014. Accessed October 2, 2019.
Tick, Beata; et al. “Heritability of autism spectrum disorders: A meta-analysis of twin studies.” The Journal of Child Psychology, December 27, 2015. Accessed October 2, 2019.
Gardener, Hannah; et al. “Perinatal and neonatal risk factors for autism: A comprehensive meta-analysis.” Pediatrics, August 2011. Accessed October 2, 2019.
Stessman, Holly; et al. “Targeted sequencing identifies 91 neurodevelopmental-disorder risk genes with autism and developmental-disability biases.” Nature Genetics, 2017. Accessed October 2, 2019.
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