The causes of autism are not fully known but involve a mix of genetic and environmental factors affecting early brain development. Vaccines do not cause autism.
What is known
Autism is neurodevelopmental. Studies estimate genetics account for 60% to 90% of risk.
Risk factors
- Genetic variants.
- Older parents.
- Premature birth or low birth weight.
- Prenatal exposure to certain drugs such as valproate.
Not causes
Vaccines do not cause autism. Large studies of millions of children found no link.
Prevalence
About 1 in 31 US 8-year-olds (CDC, 2022).
Genetics
Autism is highly heritable. Twin studies estimate heritability at about 80% or higher. Hundreds of genes have been linked to autism, each with small effects, and rare genetic changes such as de novo mutations can have larger effects. Conditions such as fragile X syndrome and tuberous sclerosis are associated with autism.
Brain development
Differences begin before birth in how the brain develops and connects. Research shows differences in brain growth, synapse formation and connectivity, though they vary a lot between individuals.
Environmental risk factors
- Advanced parental age at birth.
- Premature birth and low birth weight.
- Certain prenatal exposures such as valproic acid medication taken during pregnancy.
- Closely spaced pregnancies (less than a year).
- Maternal illness, such as uncontrolled diabetes, during pregnancy.
These factors raise the chance a small amount and are not direct causes.
What does not cause autism
Large studies including a Danish study of over 650,000 children found no link between the MMR vaccine and autism. The original 1998 paper that suggested a link was retracted in 2010. Parenting style does not cause autism. The “refrigerator mother” theory was disproven.
Prevalence
The CDC estimated in 2023 that about 1 in 36 children aged 8 had autism, up from 1 in 150 in 2000. Better awareness and broader diagnostic criteria explain much of the increase.
Signs
Early signs can include limited eye contact, no response to name by 12 months, delayed speech, repetitive movements and sensory differences.
Early support
Screening is recommended at 18 and 24 months by the American Academy of Pediatrics. Early intervention improves outcomes.
Genetics and prenatal factors
Autism spectrum disorder arises from a mix of genetic and environmental influences affecting early brain development. Twin studies estimate heritability at about 80 percent, and hundreds of genes have been linked to risk. Prenatal factors associated with higher likelihood include advanced parental age, preterm birth, very low birth weight, some maternal conditions and exposure to certain medicines such as valproate in pregnancy. Autism is not caused by parenting style.
What does not cause autism
Large studies, including a 2019 Danish study of more than 650,000 children, found no link between the MMR vaccine and autism. The CDC estimates autism affects about 1 in 31 eight year olds in the US, based on 2022 data, and it is more commonly identified in boys than girls. Early signs may appear by 12 to 18 months, such as limited eye contact, no response to name, delayed speech or no pointing. Screening at 18 and 24 months is recommended by the American Academy of Pediatrics, and early intervention services improve outcomes.
Based on data from the CDC and the American Academy of Pediatrics
