Why Autism Happens

Discover why autism happens: delve into genetic, environmental, and neurodevelopmental factors.

judah schiller
Judah Schiller
June 18, 2024
Published On
June 18, 2024

Understanding Autism

Autism, or Autism Spectrum Disorder (ASD), is a complex and multifactorial condition, with a multitude of factors contributing to its occurrence. Here, we delve into two key aspects: the role of brain development and genetic influences in the onset of autism.

Brain Development in Autism

The brain development of children diagnosed with autism exhibits a distinct pattern. Abnormal brain overgrowth is often observed during the initial two years of life, particularly affecting cerebral, cerebellar, and limbic structures that underpin higher-order cognitive, social, emotional, and language functions. This excessive growth, however, is followed by an unusually slow or even arrested growth, potentially leading to aberrant connectivity and dysfunction. These anomalies might contribute to the emergence of autistic behaviors.

Genetic Influences on Autism

While genetics play a significant role in determining the risk for developing ASD, it is important to note that genetics alone do not account for all cases of autism. Studies have revealed that autism is highly genetically heterogeneous and may be triggered by both inheritable and de novo gene variations. Hundreds of genes have been identified that contribute to the deficits in communication, social cognition, and behavior seen in patients. However, these genes only account for 10–20% of ASD cases, and individuals with similar pathogenic variants may be diagnosed at different levels of the spectrum [2].

One aspect of genetic influences on autism pertains to copy number variations (CNVs), which are submicroscopic structural variants in chromosomes that include duplications, deletions, translocations, and inversions. CNVs are estimated to directly cause approximately 10% of ASD cases, and more frequent structural variants like 16p11.2 duplications are currently being studied to better understand their contribution to autism susceptibility.

Finally, it is important to note that gene-environment interactions play a crucial role in autism risk. Studies have suggested interactions between genetic background and environmental factors such as perinatal complications, maternal immune activation, and exposure to medication during pregnancy. Animal models have shown how genetic defects in synaptic function may alter sensitivity to the environment, emphasizing the complex interplay between genetic and environmental factors in autism risk.

As we continue to explore why autism happens, it becomes increasingly apparent that a combination of genetic and environmental factors, along with specific patterns of brain development, contribute to the condition. By gaining a better understanding of these elements, we can contribute to improved diagnosis, treatments, and support for those living with ASD.

Environmental Factors

The reasons behind why autism happens extend beyond purely genetic influences and are found to be deeply intertwined with environmental factors. These factors encompass a range of influences from toxins in the environment to prenatal exposures and risks.

Toxins and Autism

Genetics strongly influence the risk for developing autism spectrum disorder (ASD), but genetics alone do not account for all instances of autism. The increasing prevalence of autism has led to interest in the potential involvement of toxins in the environment [4].

Indeed, studies are being conducted to explore the environmental influences that can increase or decrease the risk of autism. While these influences do not cause or prevent autism by themselves, they significantly influence the risk in those genetically predisposed to the disorder.

Prenatal Exposures and Risks

Prenatal exposure to chemicals like thalidomide and valproic acid has been linked to an increased risk of autism. Other environmental risk factors for autism include influences such as parental age at conception, maternal nutrition, infection during pregnancy, and prematurity.

Risk Factor Description
Parental Age at Conception Older parental age has been associated with an increased risk of autism.
Maternal Nutrition Poor nutrition during pregnancy can impact fetal brain development.
Infection During Pregnancy Maternal viral infections such as rubella, measles, mumps, and influenza during pregnancy can increase the risk of autism in the offspring due to abnormal maternal immune activation [5].
Prematurity Premature birth can increase the risk of several developmental disorders, including autism.

Maternal health, both physical and mental, during pregnancy also plays a critical role in the development of autism. Factors such as metabolic syndrome, bleeding, and infections during pregnancy are related to child autism. Maternal mental health, including conditions like depression, anxiety, and stress during pregnancy, can have irreversible effects on fetal gene expression and stress response genes, potentially leading to autism.

Additionally, maternal prenatal medication use, including antiepileptic drugs, valproic acid, and antidepressants, has been associated with an increased risk of autism in offspring. Prenatal medication use can disturb fetal development and gene expression patterns, leading to developmental delays and social behavior deficits.

Understanding these prenatal exposures and risks can contribute significantly to the understanding of why autism happens, potentially guiding prevention and improving diagnosis and treatment.

Neurodevelopmental Abnormalities

When unlocking the reasons behind why autism happens, neurodevelopmental abnormalities present compelling data. These abnormalities, which manifest early in brain development, involve both brain overgrowth and certain neuronal behaviors, and are thought to contribute significantly to autism.

Early Brain Abnormalities

Research indicates that abnormal brain overgrowth occurs during the first 2 years of life in children with autism. The most deviant overgrowth is observed in cerebral, cerebellar, and limbic structures that underlie higher-order cognitive, social, emotional, and language functions. This excessive growth is followed by abnormally slow or arrested growth, potentially leading to aberrant connectivity and dysfunction that may contribute to the development of autistic behaviors.

Moreover, two distinct neurodevelopmental abnormalities have been associated with the emergence of autism spectrum disorder. These abnormalities, which arise just weeks after the start of brain development, seem to be dictated by the size of the child's brain, and could help in the diagnosis and treatment of autism in the future.

Excitatory Neurons and Autism

In addition to early brain overgrowth, research has found links between the growth of specific types of neurons, specifically excitatory neurons, and autism. For instance, children with autism and macrocephaly exhibited excessive growth of excitatory neurons compared with their fathers. However, organoids of other children with autism showed a deficit of the same type of neurons.

The ability to track the growth of specific types of neurons could help doctors diagnose autism, as symptoms generally appear 18 to 24 months after birth [6]. Moreover, the findings from these studies may help identify autism cases that might benefit from existing drugs designed to ameliorate symptoms of disorders marked by excessive excitatory neuron activity, such as epilepsy [6].

These neurodevelopmental abnormalities provide crucial insights into the biological factors that contribute to autism. However, it's important to remember that autism is a complex disorder with a multitude of contributing factors, and these findings represent just one piece of the puzzle. Further research is needed to fully understand the intricacies of this condition and to develop effective diagnostic tools and treatments.

Impact on Neuronal Growth

Unraveling the reason why autism happens involves understanding the impact of this condition on neuronal growth. Autism has been linked to alterations in the growth of specific types of neurons, leading to potential diagnostic and treatment implications.

Neuron Growth in Autism

In children with autism, studies suggest a correlation between the condition and the growth of excitatory neurons. According to News-Medical, children with autism and macrocephaly exhibited excessive growth of these neurons compared to their fathers. Conversely, other children with autism showed a deficit of the same type of neurons.

Moreover, alterations in neurotransmitters in autism have also been reported. These include serotonin, GABA, glutamate, dopamine, norepinephrine, acetylcholine, and opioid peptides. Serotonin and GABA, in particular, have been strongly linked to autism, with alterations in these neurotransmitters impacting brain development and behavior.

Diagnostic Potential

The growth and development of neurons in individuals with autism poses potential diagnostic possibilities. The ability to track the growth of specific types of neurons, such as excitatory neurons, may aid doctors in diagnosing autism. Symptoms of autism generally appear 18 to 24 months after birth [6].

Furthermore, the findings from these studies may also provide treatment avenues. For instance, identifying autism cases that exhibit excessive excitatory neuron activity could benefit from existing drugs designed to ameliorate symptoms of disorders marked by this activity, such as epilepsy.

Understanding the impact of autism on neuronal growth, therefore, provides valuable insights into why autism happens. It paves the way for potential diagnostic tools and more targeted treatment options, underlining the importance of continued research in this area.

Health Implications

Understanding the health implications of autism is crucial to addressing the needs of individuals with this condition. This includes understanding the comorbidities often associated with autism and exploring potential treatment avenues.

Comorbidities with Autism

Autism can often co-occur with other neurological and psychiatric disorders, creating a complex health profile that requires a comprehensive treatment approach. Common comorbidities include, but are not limited to, global development delay, cognitive deficits, epilepsy, sleep disorders, Tourette syndrome, anxiety, ADHD, and mood disorders.

Comorbidity Description
Global Development Delay A condition where children take longer to reach certain development milestones
Cognitive Deficits Impairments in mental processes such as learning, memory, problem-solving, decision making, etc.
Epilepsy A neurological disorder marked by sudden recurrent episodes of seizures
Sleep Disorders Conditions that prevent a person from getting restful sleep
Tourette Syndrome A neurological disorder characterized by repetitive, stereotyped, involuntary movements and vocalizations called tics
Anxiety A mental health disorder characterized by feelings of worry, anxiety, or fear
ADHD A disorder marked by an ongoing pattern of inattention and/or hyperactivity-impulsivity
Mood Disorders A category of mental disorders characterized by a serious change in mood

Potential Treatment Avenues

In terms of treatment, there are several potential avenues being explored. One promising area of study is the role of neurotransmitters in autism. There is evidence suggesting alterations in neurotransmitters like serotonin, GABA, glutamate, dopamine, norepinephrine, acetylcholine, and opioid peptides in individuals with autism [7].

Serotonin and GABA, in particular, have been found to have strong links to autism. Alterations in these neurotransmitters can have a significant impact on brain development and behavior. Understanding these links could potentially lead to new treatment methods.

Another potential treatment avenue is the administration of hormones like oxytocin and vasopressin. Studies have shown that these hormones can alleviate autistic traits and increase social skills in animal models and humans.

These potential treatment avenues are part of ongoing research efforts aimed at improving the quality of life for individuals with autism. As our understanding of why autism happens evolves, we may see even more innovative treatment methods emerge.

Prevalence and Risk Factors

Understanding the prevalence and risk factors of autism gives us a clearer picture of why autism happens. We'll explore the increase in prevalence and the contributing factors that researchers have identified.

Prevalence Increase

Over the past two decades, the prevalence of autism has seen a significant increase. In the 1980s, the prevalence was 4-5 cases per 10,000 children. By the 1990s, it had increased to 30-60 cases, and by 2012, there were 11.3 cases per 1,000 children aged 8 years. Today, the prevalence stands at 1 in 59 children, with boys being four times more likely than girls to be diagnosed with autism.

This rising prevalence, along with the severe emotional and financial impact on families, underscores the need for large, prospective, population-based studies to elucidate modifiable risk factors, particularly those during the prenatal period [9].

Contributing Factors

Research indicates that both genetic and environmental factors play a role in the pathogenesis of autism. Genetic causes have been extensively studied, leading to the identification of specific alleles contributing to the autism spectrum. At the same time, efforts are being made to reinforce the search for environmental factors contributing to autism risk, including the study of interactions between genes and environmental factors [3].

Prenatal exposure to certain factors may also increase the risk of autism. The distinctive neuropathology of autism suggests that the aetiologically relevant period may be in utero. While there is insufficient evidence to implicate any one prenatal factor in autism etiology, the exposure to pregnancy complications may increase the risk of autism.

Overall, understanding the prevalence and risk factors of autism helps us better understand why autism happens, and provides direction for future research and potential interventions.


[1]: https://pubmed.ncbi.nlm.nih.gov/15362165/

[2]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6710438/

[3]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3513682/

[4]: https://www.autismspeaks.org/autism-environmental-factors

[5]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5377970/

[6]: https://www.news-medical.net/news/20230810/Brain-development-linked-to-the-emergence-of-autism-spectrum-disorder.aspx

[7]: https://academic.oup.com/book/29513/chapter/248024399

[8]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7139720/

[9]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3712619/