Understanding Autism: High-Risk Factors & Early Signs 

There’s a lot of information online (and unfortunately, a lot of misinformation) about what causes autism spectrum disorder (ASD). At Action Behavior Centers, we’re committed to being a trusted voice in a noisy world. We help families sort fact from fiction and offer guidance that’s rooted in science.

Autism doesn’t have one single cause. Studies show that autism develops from a mix of factors that affect how the brain develops. These are called risk factors. They don’t cause autism by themselves, but they can make it more likely for a child to receive a diagnosis.

Scientists learn more about autism every day. If you feel overwhelmed by what you’ve read or heard, you’re not alone. Our clinical team stays up-to-date on the latest research so families can get the accurate, compassionate, and reliable information they deserve.

Are children born with autism?

Autism spectrum disorder is a developmental condition. Children may not show obvious signs at birth, but early signs often appear in the first years of life as they grow and develop. Researchers believe autism is linked to brain development and genetics, not something that suddenly “happens” later in childhood.

What are the first signs of autism?

Autism often becomes noticeable between 12 and 18 months, though some signs may appear earlier. Common early signs include:

• Limited interest in playing or interacting with others
• Reduced eye contact or facial expressions
• Delays in speech or language development
• Repetitive movements, such as hand-flapping or rocking
• Strong attachment to routines and difficulty with changes
• Sensitivity to sounds, textures, or other sensory input

If you notice any of these signs, talk with your child’s pediatrician. Autism screening and early intervention can make a meaningful difference in supporting your child’s growth and helping them learn new skills.

What causes autism?

Is autism genetic?

Autism is thought to develop from both genetics and the environment. Research shows that genetics plays a strong role. Scientists have found hundreds of genes linked to autism, many of which affect how the brain develops and how brain cells communicate. Environmental factors may add to this risk, although researchers are still learning how genes and the environment interact.¹

Autism often runs in families. If one child is diagnosed, their brothers or sisters have a higher chance of being diagnosed as well. About 20% of younger siblings of autistic children receive an ASD diagnosis, a rate seven times higher than that of the general population.² 

Some chromosomal conditions are also associated with a higher likelihood of autism. According to the Centers for Disease Control and Prevention (CDC), children with fragile X syndrome receive ASD diagnoses more often.⁴ Knowing which genes and chromosomal changes are linked to autism helps researchers ask better questions and develop more accurate diagnostic tools.

Which parent carries the autism gene?

Autism spectrum disorder does not come from a single gene. Instead, many genes and environmental factors interact in complex ways. Both parents contribute genetic variations that may increase the chance that a child develops autism, so no single parent “carries” an autism gene.¹ 

Environmental influences before & during pregnancy

Genes play a major role in autism, but research shows that certain environmental factors during pregnancy may also influence how autism develops. These factors don’t cause autism on their own. Instead, they may interact with genetic risk in ways that shape early brain development. This helps explain why autism can look different from child to child.

Studies have found associations between autism and:

• Advanced parental age
• Pregnancy complications
• Maternal infections with fever during pregnancy
• Prenatal exposures, including certain medications, toxins, or high air pollution levels

Researchers believe these factors may influence brain development through mechanisms such as immune system changes, inflammation, cell stress, or shifts in the maternal microbiome. While more studies are needed, continued research helps doctors and scientists look for ways to support healthier pregnancies and early development.⁵ 

Birth complications & early brain injury

Some birth complications may raise the risk for autism, such as:

Premature birth (36 weeks or earlier)

Breech presentation, induced or no labor, preeclampsia, and fetal distress

Low birth weight

Postpartum hemorrhage

Presence of brain anomalies

Children who experience a serious brain injury early in life may also face a higher risk. In one study of over 500 children who experienced an acquired brain injury before age 2, about 2.7% later received an autism spectrum disorder diagnosis. On average, these children received their diagnosis nearly five years later than typical. Many also had other health challenges that may have masked early autism symptoms.⁷

It’s important to remember that risk factors do not guarantee an autism diagnosis. Many children with these risk factors never receive a diagnosis, while some children diagnosed with autism do not have any known risk factors.

How do clinicians diagnose autism?

Clinicians diagnose autism through screenings, evaluations, and standardized diagnostic tools. Developmental pediatricians, psychologists, and neurologists often lead this process.

The steps usually include:

1. Developmental screening

Pediatricians at well-child visits may use questionnaires to identify potential red flags for autism. Parents can also complete screeners like the M-CHAT-R and CAST at home.

2. Comprehensive autism evaluation

If screening suggests signs of autism, your child may receive a referral for a full diagnostic evaluation. This evaluation may include:

• Autism specific tests such as the ADOS-2 or CARS-2.
• Parent interviews and developmental history questionnaires
• Direct observation of communication, play, and social interaction

3. Multidisciplinary input (if needed)

In some cases, autism assessments may include input from speech-language pathologists, occupational therapists, or educators, especially if multiple areas of development appear impacted.

Get started with ABA therapy for autism

From your family’s first questions to your child’s next milestone, we’re here to support you. Find an ABA therapy center near you today to get started.