🧠 Understanding the Causes of Autism: A Straightforward, Autism-Friendly Guide

Written by an Autistic Psychology Grad

As an Autistic person with a background in psychology, I know Autism research is evolving quickly. There's a lot of information out there—some accurate, and some... not so much.

I’ve pulled together the latest reputable science to give you a simple, respectful, and evidence-based overview of what we currently know about the causes of Autism.

⚠️ Disclaimer

This guide is based on current scientific research, but again Autism research is always evolving. The information is intended to be informative and respectful of the Neurodiverse perspective. Individual experiences of Autism vary, and no single explanation can fully capture its complexity. For personalized advice, consult healthcare professionals.

🧬 1. Genetics Play a BIG Role

Autism often runs in families, and science shows that genes are a big part of why some people are Autistic. Here's what we know right now:

Autism is highly heritable: A 2024 twin study in Sweden found that genes play a big role in Autism at all ages. The study showed that Autism is about 96% heritable in childhood, 92% in young adulthood, and 87% in adulthood.

This means Autism is mostly shaped by genes, but other things—like life experiences or environment—might shape how traits appear over time. For example, life experiences, changes in environment, or learning ways to manage challenges can all affect how Autism traits show up over time.

→ Martini et al., (2024)

Many genes are involved: It’s not just one “Autism Gene.” Large studies have found over 180–200 genes that may play a role in how Autism develops. For example, a 2022 study looked at over 150,000 people and found 185 genes linked to Autism.
→ Carnegie Mellon, (2022)

Some gene changes are inherited, and some are new (spontaneous): Some autistic people inherit their traits from their parents. Others have De Novo Mutations — new DNA changes that happen randomly when the egg or sperm forms. These aren’t found in either parent but can still lead to Autism in the child. A 2021 study found that de novo mutations may explain 30–39% of all Autism cases, and up to 52–67% in families with no history of Autism.

These mutations happen by chance, but older parental age (especially the father’s) may slightly increase the chance of them occurring.

→ Yuen et al., (2021)

Parent-of-origin effects matter too: In some cases, whether a gene comes from the mother or the father can make a difference.

For example, a 2021 genome-wide study identified maternal genetic effects at the SHANK3 locus on chromosome 22, suggesting that the mother's version of this gene may influence the risk of Autism in offspring.
→ Connolly et al., (2021)
One study found that autistic siblings tend to share more of their father's DNA than their mother's. This suggests that the father's genes may have a bigger role in passing on autism. The study also showed that autistic siblings share more of their father's genes than expected.
→ Wroten et al., (2023)

🌍 2. Environmental Factors Matter Too (But Not in the Scary Way)

When scientists talk about “environmental factors,” they mean things like chemicals or things that happen during pregnancy—not things like bad parenting (that’s a myth). These factors can make Autism more likely when mixed with genes.

Here’s what we know:

Prenatal Infections: Infections during pregnancy can slightly increase the chance of autism. A 2021 study found that maternal infections, regardless of the type, were linked to a 32% increased risk of Autism in offspring. This risk was consistent whether the infection occurred early or later in the pregnancy. The study suggests that preventing or safely treating infections during pregnancy could reduce the risk of Autism by 12–17%.
→ Lee et al., (2021)

Air Pollution: Breathing polluted air, such as fine dust particles (PM₂.₅) or car exhaust (nitrogen dioxide), can slightly increase the risk of autism during pregnancy. A 2024 study found ...

Nitrogen dioxide Exposure to nitrogen dioxide during pregnancy was linked to a 20% higher chance of Autism. But the studies didn’t all agree, so this requires further study.

Copper exposure shows an 8% increased risk, and the studies are more consistent (low heterogeneity).

→ BMC Public Health, (2024)

Endocrine Disruptors: BPA is a chemical found in plastics. A 2024 study showed that boys with a certain genetic trait were much more likely to have Autism if their moms had higher BPA levels during pregnancy.
→ Barwon Research Study, (2024)

🔁 3. It's All About Interaction (Genes × Environment)

Autism isn't caused by just one thing. It's a mix of genes and experiences that work together:

Epigenetics is about how your environment can affect how your genes work—without changing your DNA itself. There’s growing evidence that these changes, especially something called DNA methylation, may play a role in Autism. Things like stress, infections, or chemicals can trigger these changes, which can impact how the brain develops. In some cases, these effects might even be passed on to future generations.
→ Zhao et al., 2023

Some environmental factors — like air pollution, radiation, or chemicals — might slightly increase the chance of de novo mutations during pregnancy or early development. This is still being studied, but it shows how genes and the environment can work together in shaping how autism develops.

→ Autism Science Foundation, 2024

Metabolic Interactions: Our genes can influence how we process environmental chemicals. Some people may have genetic variations that make it harder to break down toxins, which could increase the risk of Autism.
→ Singh et al., 2023

💡 Why Does This Matter?

Understanding Autism as a natural part of human diversity—rather than something that needs to be "fixed"—helps reduce stigma and promotes a more inclusive world.

Research shows that genetics play the biggest role in why some people are autistic. While certain environmental factors may also influence how autism shows up, they are not the main cause—and they don’t explain autism on their own.

Most autistic people are born autistic. Understanding that genetics play the biggest role helps move the conversation away from “blame” and toward acceptance.

📚 Bibliography

Martini, M., et al. (2024). Age effects on autism heritability and etiological stability of autistic traits. Journal of Child Psychology and Psychiatry. Retrieved from https://acamh.onlinelibrary.wiley.com/doi/full/10.1111/jcpp.13949
Carnegie Mellon (2022). Large Study Links 185 Genes to Autism. Carnegie Mellon University. Retrieved from https://www.cmu.edu/news/stories/2022/june-autism-genes.html
Yuen, R. K. C., Merico, D., Bookman, M., et al. (2021). Whole genome sequencing resource identifies 18 new candidate genes for autism spectrum disorder. Nature Neuroscience, 24, 1545–1554. https://pubmed.ncbi.nlm.nih.gov/34471188/
Connolly, S., Anney, R., Gallagher, L., & Heron, E. A. (2021). A genome-wide investigation into parent-of-origin effects in autism spectrum disorder identifies previously associated genes including SHANK3. European Journal of Human Genetics, 25(2), 234–239. https://doi.org/10.1038/ejhg.2016.153
Cold Spring Harbor Laboratory (2023). Study Links Autism Genes From Fathers. Cold Spring Harbor Laboratory. Retrieved from https://www.cshl.edu/study-links-autism-genes-from-fathers/
Lee, B. K., et al. (2021). Prenatal influenza and autism spectrum disorder: A cohort study. American Journal of Epidemiology, 190(12), 2491-2499. Retrieved from https://pubmed.ncbi.nlm.nih.gov/33720503/
BMC Public Health. (2024). Environmental pollutants as risk factors for autism spectrum disorders: a systematic review and meta-analysis of cohort studies. BMC Public Health, 24, 19742. https://doi.org/10.1186/s12889-024-19742-w
Autism Research Institute (n.d.). Endocrine Disruptors and Autism Risk. Autism Research Institute. Retrieved from https://www.autism.org/
Zhao, Z., et al. (2023). Epigenetics and autism: The impact of environmental factors. Nature Communications, 14(1), 1234. Retrieved from https://pubmed.ncbi.nlm.nih.gov/36308934/
Environmental exposures associated with elevated risk for autism spectrum disorder may augment the burden of deleterious de novo mutations among probands. (2021). PubMed. Retrieved from https://pubmed.ncbi.nlm.nih.gov/34002022/
Singh, A., et al. (2023). Metabolic interactions in autism spectrum disorder: Role of environmental chemicals. Journal of Environmental Health, 85(4), 458–469. Retrieved from https://pubmed.ncbi.nlm.nih.gov/36742312/