What We Know (and Don’t Know) About the Causes of Autism
By Dr. Pete, Emergency Physician, Professor, and Relentlessly Practical Dad
For decades, scientists have been trying to understand why autism spectrum disorder (ASD) develops. The research has been massive — spanning genetics, brain biology, environmental science, and public health. Over the past 30 years alone, well over 3,000 published studies have investigated potential causes of ASD across multiple scientific fields.
Genetics plays a major role. Twin and family studies show that genetic factors explain about 64–91% of the risk for autism, with large population studies estimating heritability between 66–83% (Hirota & King, 2023; Bai et al., 2019; Muhle et al., 2018). Researchers have identified over 100 rare genetic mutations — including changes in genes such as CHD8, SHANK3, and NRXN1 — along with thousands of more common genetic variations that each contribute small amounts of risk (Horecka-Lewitowicz et al., 2024). Still, no single genetic change is necessary or sufficient to cause autism.
Environmental factors matter too — but they’re complicated. Studies have explored prenatal and early life exposures, including advanced parental age, maternal diabetes, certain medications during pregnancy (like valproic acid), premature birth, and high levels of air pollution (Bölte et al., 2019; Yenkoyan et al., 2024; Lyall et al., 2017). Some of these factors show modest associations with autism, but most do not cause it on their own, and many are influenced by underlying genetics.
The bottom line: Autism likely develops from a complex interaction between genes and environment, with no single “smoking gun.”
Vaccines and Autism: What the Evidence Really Says
There is robust, consistent, and high‑quality evidence that vaccines do not cause autism. This has been studied more thoroughly than almost any other medical question.
A 2014 meta‑analysis pooling data from over 1.2 million children in cohort studies and nearly 10,000 children in case‑control studies found no link between any vaccine — including the measles‑mumps‑rubella (MMR) vaccine and vaccines containing thimerosal — and autism (Taylor et al., 2014). This study was conducted independently by academic researchers and was not funded by vaccine manufacturers.
A nationwide Danish cohort study following more than 650,000 children also found no increased autism risk after MMR vaccination, even in children at higher genetic risk such as those with autistic siblings (Hviid et al., 2019). This work was supported by the Danish Ministry of Health and independent research grants, without industry funding.
Multiple systematic reviews and meta‑analyses, including those sponsored by the U.S. Agency for Healthcare Research and Quality (AHRQ) and conducted by the RAND Corporation, have rated the strength of evidence as high that MMR and other routine childhood vaccines are not associated with autism (Gidengil et al., 2021; Maglione et al., 2014). The Institute of Medicine (now the National Academy of Medicine) has also concluded there is no causal relationship between MMR or thimerosal‑containing vaccines and autism (Bester, 2016).
📦 The Wakefield Scandal in Brief — Why the 1998 MMR–Autism Paper Was Retracted
🛑 What Happened
In 1998, British gastroenterologist Andrew Wakefield published a small case series in The Lancet suggesting a link between MMR and autism. It caused worldwide alarm — but the study has been completely discredited.
🚨 Ethical and Scientific Violations (UK General Medical Council Findings)
💰 Hidden Financial Conflicts — Wakefield was paid by lawyers preparing lawsuits against MMR manufacturers and had filed a patent for a rival measles vaccine — none of which was disclosed.
🔬 Unapproved Invasive Procedures — Children underwent colonoscopies and lumbar punctures without proper ethical approval or medical necessity.
✏️ Data Misrepresentation — Patient records were altered to exaggerate the timing link between MMR vaccination and autism symptoms.
🎯 Biased Recruitment — Several participants were referred through anti‑vaccine activists rather than neutral medical channels.
⚖️ Consequences
The Lancet fully retracted the paper in 2010.
Wakefield was stripped of his medical license in the UK.
No credible research since has supported his claims.
📢 The Takeaway
The MMR–autism scare came from fraudulent, unethical research. The true weight of scientific evidence — based on millions of children worldwide — shows vaccines do not cause autism.
Parent Takeaway
Autism is a neurodevelopmental condition with complex causes, mostly driven by genetics, and sometimes influenced by early-life environmental factors.
Vaccines are not one of those factors — the science is clear, repeated, and high-quality.
The idea that MMR or other vaccines cause autism began with a single fraudulent paper, and decades of research have proven it wrong. Vaccinating your child protects them and the community without increasing autism risk.
References
Bai D, Yip BHK, Windham GC, et al. (2019). Association of Genetic and Environmental Factors With Autism in a 5‑Country Cohort. JAMA Psychiatry, 76(10), 1035‑1043. doi:10.1001/jamapsychiatry.2019.1411
Bester JC. (2016). Measles and Measles Vaccination: A Review. JAMA Pediatrics, 170(12), 1209‑1215. doi:10.1001/jamapediatrics.2016.1787
Bölte S, Girdler S, Marschik PB. (2019). The Contribution of Environmental Exposure to the Etiology of Autism Spectrum Disorder. Cellular and Molecular Life Sciences, 76(7), 1275‑1297. doi:10.1007/s00018-018-2988-4
Gidengil C, Goetz MB, Newberry S, et al. (2021). Safety of Vaccines Used for Routine Immunization in the United States: An Updated Systematic Review and Meta‑Analysis. Vaccine, 39(28), 3696‑3716. doi:10.1016/j.vaccine.2021.03.079
Hirota T, King BH. (2023). Autism Spectrum Disorder: A Review. JAMA, 329(2), 157‑168. doi:10.1001/jama.2022.23661
Horecka‑Lewitowicz A, Lewitowicz W, Wawszczak‑Kasza M, et al. (2024). Autism Spectrum Disorder Pathogenesis — a Cross‑Sectional Literature Review Emphasizing Molecular Aspects. International Journal of Molecular Sciences, 25(20), 11283. doi:10.3390/ijms252011283
Hviid A, Hansen JV, Frisch M, Melbye M. (2019). Measles, Mumps, Rubella Vaccination and Autism: A Nationwide Cohort Study. Annals of Internal Medicine, 170(8), 513‑520. doi:10.7326/M18-2101
Lyall K, Croen L, Daniels J, et al. (2017). The Changing Epidemiology of Autism Spectrum Disorders. Annual Review of Public Health, 38, 81‑102. doi:10.1146/annurev-publhealth-031816-044318
Maglione MA, Das L, Raaen L, et al. (2014). Safety of Vaccines Used for Routine Immunization of U.S. Children: A Systematic Review. Pediatrics, 134(2), 325‑337. doi:10.1542/peds.2014-1079
Muhle RA, Reed HE, Stratigos KA, Veenstra‑VanderWeele J. (2018). The Emerging Clinical Neuroscience of Autism Spectrum Disorder: A Review. JAMA Psychiatry, 75(5), 514‑523. doi:10.1001/jamapsychiatry.2017.4685
Taylor LE, Swerdfeger AL, Eslick GD. (2014). Vaccines Are Not Associated With Autism: An Evidence‑Based Meta‑Analysis of Case‑Control and Cohort Studies. Vaccine, 32(29), 3623‑3629. doi:10.1016/j.vaccine.2014.04.085
Yenkoyan K, Mkhitaryan M, Bjørklund G. (2024). Environmental Risk Factors in Autism Spectrum Disorder: A Narrative Review. Current Medicinal Chemistry, 31(17), 2345‑2360. doi:10.2174/0109298673252471231121045529
Author’s Note on Content Creation
I use AI tools like ChatGPT and Gemini in an iterative workflow to help with reference cross-checking, fact validation, and initial drafts. The final tone, structure, humor, and all opinions remain my own as an emergency physician, educator, and parent. These articles reflect my writing, my judgment, and my voice—with a little help from the robots.