Risk Factors & Causes of Autism Spectrum Disorder

December 13, 2024

Learn about autism's risk factors and causes, from genetic to environmental influences. Understand the latest research and common misconceptions about ASD.

Risk Factors & Causes of Autism Spectrum Disorder

Both genetic and environmental influences can increase the risk of autism and shape the type of autism a child can develop. Contrary to common misconceptions, autism has nothing to do with parenting style, vaccines, foods, or anything else a child encounters after birth or early childhood development. ASD is typically something you are born with. It’s not something one can develop later in life.

Autism Causes and Risk Factors

It’s important to note that there has been no single definitive cause identified for the development of ASD. Autism is multifactorial and is believed to develop due to a combination of both genetic and environmental influences. Let’s first explore these common genetic and environmental factors that cause autism.

Environmental Causes of Autism

Studies show that around 80% of autism cases are linked to inherited genetic mutations. However, it does not account for all instances of autism. Environmental influences have also been linked to increased risk of ASD. These environmental causes include:

Prenatal Exposures

The following prenatal exposures may interact with genetic predispositions which may influence the likelihood of autism.

Maternal infections

Certain infections such as rubella, CMV, and influenza during pregnancy were associated with the onset of autism. Infections may alter the activity of many genes linked to autism, which may cause changes in brain anatomy.

Exposure to certain medications

One of the most strongly linked medications to autism is antiepileptic drugs like valproic acid. Antidepressants like SSRIs prescribed for anxiety, depression, and mood disorders may also slightly contribute to the condition. Other associated medications include acetaminophen, asthma medications, painkillers, and illicit drugs.

Maternal stress

Stress alone does not cause autism but could be a contributing factor. Elevated cortisol levels can cross the placenta and may affect the fetal brain development. This may cause structural changes in the fetal brain which can contribute to autism-related behaviors.

Maternal obesity

Children born to obese mothers have an increased risk of behavioral and neuropsychiatric conditions including ASD and ADHD. Obesity may cause inflammatory, metabolic, and hormonal disruptions during pregnancy that can affect the development of the fetal brain.

Maternal diabetes

Diabetes affects the levels of oxygen, insulin, and inflammation in the womb, changing the environment in which the fetal brain forms. Plus, it can raise the risk of oxidative stress which can interfere with healthy neural development and fetal growth.

Maternal smoking

Nicotine can affect the receptors that are crucial for growing neurons. Plus, smoking reduces the fetal oxygen supply, which can further harm or delay brain development.

Maternal substance abuse

Whether or not it causes autism, illegal drug use is harmful to the baby. If it’s not ASD, other similar symptoms like speech delay or behavioral problems can manifest. Although there is not enough evidence that correlates ASD and marijuana or opioid use, using any illegal or street drugs during pregnancy can have a serious effect on the unborn child.

Prenatal Nutrition

While more research is needed to further support the correlation between autism and prenatal nutrition, studies show that essential nutrients can play a critical role in fetal brain development. Other complications can also be reduced including preterm birth, gestational diabetes, low birth weight, and infections.

Certain vitamin and mineral deficiencies like Folic Acid (Vitamin B9) and Vitamin D are also associated with the increased risk of autism. Thus, folic acid, Vitamin D, and multivitamin supplementation during pregnancy is typically a core part of prenatal care.

Take note that the above-mentioned associations may not imply causation. Some exposures like medication use and maternal infections are better supported by research while some are still areas of ongoing study such as air pollution and nutritional deficiencies.

Early Life Environmental Factors

Early-life exposure to air pollution and toxins like pesticides and heavy metals may be a risk factor for autism. Fine particulate matter (PM2.5), nitrogen dioxide (NO2), and other air pollutants have been linked to the development of ASD. Exposure especially during the third trimester of pregnancy can affect the fetal brain development. Even postnatal exposure has been associated with adverse neurodevelopmental outcomes.

Parental Factors

Older parents are more likely than young ones to have a child with autism. The effect of paternal age is especially consistent in many findings. The odds don’t necessarily rise after a certain age but just steadily increase over time. According to a 2014 study, children born to fathers 45 years old or above have 75% higher chances of having autism among other conditions as compared to fathers in their 20s.

Maternal age’s effects on autism development are not as clear-cut as they are for paternal age. However, some studies suggested that the number of de novo mutations in egg cells increases as women age– though to a lesser degree than it does in sperm. Overall, the trend toward later parenthood only accounts for 1-5% of the increase in autism prevalence according to independent studies.

Birth complications

Studies show that pregnancy and delivery complications can increase the odds of having a child with autism by at least 26%. These factors include abnormal position of the baby in the womb, birth complications that lead to periods of oxygen deprivation to the infant’s brain, and serious blood pressure conditions. Other risk factors linked to birth complications and ASD are extreme prematurity or very low birth weight.

Birth Spacing

According to a new study, mothers of children with ASD may reduce the odds of having another autistic child if they time a second pregnancy to occur after 2.5 to 3 years. Short birth spacing, particularly intervals of less than 12 months, can significantly increase the risk of any type of ASD.

Genetic Causes of Autism

Autism susceptibility is currently estimated to be 50-80% genetic. It’s an inherited disorder for the most part. If you have a child with ASD, you are more likely to have another autistic child. Your family members are also more likely to pass on the genes.

Which gene causes autism?

Autism is a polygenic disorder. Thus, it involves many variations in many genes. It’s hard to identify the exact causative genes, and there are over 100 genes associated with autism. However, researchers found seven potential genes that are likely to increase ASD susceptibility including PRR25, PLEKHA8, VPS54, FBXL13, SNCAIP, SLFN5, and TGM1.

Who Carries the Autism Gene: Mother or Father?

Scientists found a stronger genetic component from the father that contributed to ASD diagnoses in siblings. This does not conclude that the father carries the autism gene in every case, but research found that autistic siblings are nearly twice as likely to share genetic material from their father compared to their mother.

What Are De Novo Mutations?

Certain mutations that can lead to autism are not inherited from either parents or grandparents. These spontaneous mutations or genetic alterations that appear in a family for the first time are called de novo mutations.

De novo mutations have been linked to advanced paternal age, DNA replication errors, exposure to environmental agents, or just natural and random mutations during the early stages of embryonic development with no specific trigger.

Genetics of Autism

Other genetic mechanisms and tendencies of autism prevalence are as follows:

Boys are 4-5 times more likely than girls to be diagnosed with autism.
Gender-related differences in symptoms are often seen in social understanding, communication, and imagination.
Many individuals with autism spectrum disorder (ASD) also experience co-occurring medical conditions such as allergies, asthma, epilepsy, digestive and feeding disorders, sleep disturbances, sensory integration issues, cognitive impairments, and other health concerns.
Children with autism tend to have lower bone density than their non-autistic peers.
Up to one-third of people with ASD develop seizure disorders, with a seizure rate 10 times higher than in the general population.
Around 10% of individuals with ASD also have another neurological, genetic, or metabolic disorder.
Children with an older sister on the autism spectrum are more likely to develop the condition than those with an older brother. Younger brothers are at greater risk than younger sisters.

FAQ

Can two autistic parents have a neurotypical child?

Yes. Even if both parents are autistic, it’s likely that a child inherits a different combination of genres that do not cause ASD. Autism has very complex inheritance patterns, unlike other simple traits like hair or eye color.

Can vaccines cause autism?

Vaccines do not cause autism. There is no scientific proof supporting that any type of vaccine is associated with ASD.

Why is autism increasing?

Rather than an actual rise in autism prevalence, the increase in autism rates nowadays may just be due to the growing awareness and advocacy of autism; expanded diagnostic criteria; and better screening tools than ever before.

Is there a way to prevent autism?

Although prenatal care can help reduce the risk of autism among newborns, there is no definite way to prevent autism due to the complexity of its underlying causes. While guaranteed prevention is not possible, early diagnosis and intervention can greatly improve outcomes.

Can autism be cured?

Autism is not an illness that can be cured. It’s a lifelong neurodevelopmental condition. It’s a matter of natural differences among people just like how people differ in personality and physical traits. However support and intervention can help improve the lives of autistic individuals with difficulties in communication, social, and adaptive skills.

Conclusion

It’s important to consider the Autism Spectrum Disorder as a ‘difference’ rather than a disadvantage. Early diagnosis and intervention are crucial to help children with autism improve their language development, daily living skills, and adaptive behavior. One such intervention is DIR Floortime, which emphasizes meaningful connections and individual growth.

At WonDIRfulPlay, we celebrate these differences and provide tailored support for children and families navigating autism. With evidence-based therapies like DIR Floortime, we strive to create an environment where every child can thrive. Get in touch to learn how we can help your family on this journey!

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