Is Autism Genetic?

Yes. Autism is genetic. 

However, genetics aren’t the only reason behind it. A recent study published in 2019 estimates that:¹

• 20 percent of diagnosed autism isn’t genetically influenced
• Environmental risk factors “contribute minimally” to autism

This means that while autism is usually inherited, both genetic and non-genetic factors increase a child’s risk.

Moreover, there is no single gene that causes autism. Research shows that several gene variations related to brain development are linked to the condition.²

What is Autism Spectrum Disorder?

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that appears in young children as early as one to two years old. 

People with this developmental disorder have a neurologic condition. This means that there’s something different about their nervous system.

Neurodevelopmental disorders interfere with people’s ability to learn and apply information and skills. A person with autism tends to struggle with:

• Social interaction       
• Communication 
• Repetitive behaviors

Autism can affect a person’s ability to function at work, school, and in social environments. The severity of autistic traits can vary for each person.

Is Autism Passed Down Genetically?

Yes. Autism can be genetically passed down from parent to offspring. If one or both parents have autism-causing genes, children can inherit them.

The latest genetic research suggests that children are more likely to inherit the autism gene from their father.²

While mothers pass half of their structural variants to a child, fathers pass much more than 50 percent of their genetic mutations to children.² 

Structural variants are DNA sequences that underwent major changes or mutations–such as duplication, deletion, or inversion. 

This increases the likelihood of passing the genetic risk for autism, along with other genetic disorders.

Sometimes, these mutations affect children and cause autism. But a child can also inherit the same mutations without developing the condition.

Sporadic Autism Spectrum Disorders

Not all autism disorders are hereditary. Others are sporadic or occur randomly.

Unaffected parents can still give birth to autistic children. Half of these autism cases are caused by spontaneous mutations that are not present in the parent.³ 

A spontaneous mutation can occur in the father’s sperm or the mother’s egg and increase a child’s genetic predisposition for autism.³ 

A developing embryo may also undergo genetic changes when exposed to certain environmental factors before birth. 

During this time, they can develop the “risk genes” associated with autism. 

What Are Other Causes of Autism?

Autism arises from both genetic influences and environmental factors. The following non-genetic factors are known to increase a child’s autism risk:⁴

• Conceiving at an old age
• Exposing an unborn baby to certain pesticides or pollution
• If the pregnant mother has obesity, diabetes, or immune system disorders 
• Being born prematurely or with a very low birth weight
• Difficult childbirth that deprives the baby’s brain of oxygen

Why is It Important to Know Your Family Health History?

Autistic spectrum disorders tend to run in the family. If a family member has autism, it’s likely that you have autism or will have an autistic child.

Doctors aware of this family history can screen everyone (including unaffected family members) and identify autistic individuals.

Since affected children don’t always show signs of autism, screening ensures they are diagnosed and treated as soon as possible.

People who are planning a pregnancy or who are already pregnant can take this information to a doctor. The doctor will use it to determine your likelihood of having autistic children.

How is Autism Diagnosed?

Doctors usually diagnose autism by looking into a child’s history. They will check for signs of developmental delay and other autistic symptoms.

ASD can be diagnosed at 18 months old or even younger. However, a diagnosis by the age of two is usually considered more reliable.

In some cases, the doctor will continue to monitor the affected child and may not make a final diagnosis until they are much older.

Unfortunately, this can prevent them from getting the support they need to reach their full potential. 

How Genetic Testing Can Help

Children diagnosed with autism are often asked to undergo DNA testing. 

The doctor might order a chromosomal microarray (CMA) to examine your chromosomes, or a whole exome sequence test to look at your exomes.

Both genetic tests can identify genes involved in the development of autism. 

You can take these results to a doctor or genetic counselor who can explain their meaning. They can use this information to help you decide on the next steps.

DNA tests can also check for other genetic conditions that may be causing your autism. Some examples include:

• Fragile X syndrome – a disorder that affects 1 in every 200 people with ASD and causes intellectual disability
• Rett syndrome – a disorder that affects 4 percent of women with ASD

This can help doctors determine the best treatment for your condition.