What Causes Autism?

With more attention being paid to spectrum disorders, including autism, and a noticeable increase in autism diagnoses, you may be wondering what causes autism and whether autism is genetic or environmental.

Causes of autism are complex. Some children and adults have different levels of autism as defined in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5).

Autism, Causes, and the Brain

There is no known root cause or a single cause of autism, and both genetic and environmental factors are involved. 

Research in the past decade has identified hundreds of genes contributing to communication, social cognition, and behavioral differences present in autism spectrum disorder (ASD). According to a 2019 medical review on genetic causes of autism, these genes may be inherited (passed down in families) or show up in genetic variations not previously seen in the family.

Other factors associated with autism include:  

• Advanced or older parental age
• Very low birth weight
• Extremely premature birth
• Neonatal jaundice  (having a high level of bilirubin, a blood waste product, at birth)
• Pregnancy complications
• Birthing complications 
  
• Immune system disorders
• Traffic-related air pollutants associated with genetic mutation 
• Excessive parental stress
  
• Emotional injury or trauma

What Is Known

Researchers describe autism as a neurodevelopmental disorder with causes linked to a complex combination of genetics and environmental factors. They also acknowledge the causes of autism are more complicated than that. Parenting style does not cause autism, and parents don’t cause the difficulties associated with autism.

What Is Not Known

There is no consensus on what causes autism.

Some people with autism have higher support needs than others, although it isn’t always clear why. The amount of support a person with autism needs may vary. A combination of factors is likely at play. For example, if someone has a comorbid condition (a co-occurring health condition), such as a learning disability and/or psychiatric condition, it may compound support needs and accommodations. 

Who Is More Likely to Develop Autism?

Autism is found across genders, races, ethnicities, and economic backgrounds. People who may be more likely to develop autism include those with:

• Older parents
• A sibling with autism
• Very low birth weight (premature birth)
• Certain genetic conditions including Down syndrome 

Pregnancy and Autism Causes

During pregnancy, metabolic conditions like excessive pregnancy weight gain, obesity, and gestational diabetes (diabetes during pregnancy) are associated with glucose metabolism dysfunction, affecting brain energy production. 

One 2019 study suggests metabolic disorders like hypoglycemia (low blood glucose) during pregnancy may be a contributing factor to a child having autism. High blood sugar or hyperglycemia after birth may also play a role, according to the same study.

Other pregnancy complications contributing to (but not causing) the risk of autism include:

• Fever
• Exposure to contaminants causing genetic mutations in the child

Birthing complications, including a reduced oxygen supply to the child’s brain. When pregnant, inform your healthcare provider of any medications you are taking. One anti-seizure medication Valporaote (depakene), in particular, is associated with an increased chance of autism development in the child.

Causes of Undiagnosed Autism in Adults 

Autism can go undiagnosed for several reasons. It can be mistaken for mental health disorders such as:

• Obsessive-compulsive disorder (OCD)
• Social anxiety disorder (SAD)
• Separation anxiety disorder
• Attention-deficit hyperactivity disorder (ADHD)

Additionally, autism's diagnostic criteria were revised in the DSM-5, meaning people born before these revisions may have gone undiagnosed.

Gender Disparities

Researchers argue there has been a gender gap in autism research and understanding that lead to more men being diagnosed with autism and women frequently being undiagnosed. This has led to a biased, male-centric understanding of autism and created barriers to understanding how autism develops in girls and women.

Racial Disparities

Research shows systematic racial bias and cultural misperceptions result in missed autism diagnosis and underdiagnosis in Black, Latinx, and Asian children—and that children of color are not being diagnosed until later in life, if at all.

Summary

Autism can develop in anyone, but there are several genetic and environmental factors contributing to it. More research is needed to understand the root causes of autism. Changes in diagnostic criteria and gender and racial disparities have caused people to go undiagnosed.