Causes of Autism Spectrum Disorder

11 Jan 2022

Explore the causes of autism spectrum disorder, from genetic factors to environmental influences, and understand their impact on development.

Understanding Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a complex and multifaceted condition, and understanding its nuances is key to unraveling the causes of autism spectrum disorder.

Defining Autism Spectrum Disorder

ASD is a neurological and developmental disorder that affects how individuals interact with others, communicate, learn, and behave. It is a developmental disability characterized by impairments in social interactions, abnormalities in speech, and stereotyped patterns of behavior, with onset usually occurring in childhood under 3 years old [1].

The term "spectrum" in ASD reflects the wide variation in the type and severity of symptoms people experience. ASD can affect people of all genders, races, ethnicities, and economic backgrounds [2].

The Spectrum of Symptoms

Symptoms of ASD typically appear between 12 and 18 months of age, with sensory and motor symptoms often occurring earlier, during the first 12 months. Some children may show a loss of previously developed abilities between 18 and 24 months. Early signs of ASD may include a lack of response to names, poor eye gaze, decreased shared attention, and narrow usage of deictic gestures.

Youngsters with severe ASD symptoms exhibit more social deficits in communication and interactions, increased restricted and repetitive behaviors, and show higher levels of these behaviors compared to children with milder ASD symptoms. Core symptoms may include atypical social and communication development with impaired facial emotion recognition [3].

The wide range of symptoms and their varying degrees of severity underline the complexity of ASD. Understanding these symptoms is critical to learning about the causes of autism spectrum disorder, which is explored in the following sections of this article.

The Genetic Factors

Exploring the causes of autism spectrum disorder (ASD), a significant body of research points to genetic factors. These genetic influences are believed to account for an estimated 80% of the risk for ASD, with environmental factors contributing approximately 20% [4].

Inheritance and Autism

The role of inheritance in ASD is substantial, with heritability estimates ranging from 50% to over 90%. Twin studies have further highlighted this genetic influence, showing higher concordance rates for autism and related disorders amongst monozygotic twins compared to dizygotic twins. However, the independent heritability of different domains of autistic symptoms continues to be a topic of debate.

Specific Genetic Contributions to Autism

There are various genetic factors implicated in the etiology of ASD. This includes de novo mutations, copy number variants, and common variants. Specifically, de novo mutations in genes such as CHD8 and SCN2A have been associated with an increased risk of ASD [5].

Furthermore, the prevalence of de novo chromosomal rearrangements is higher in subjects from simplex families (those with one affected individual) compared to subjects from multiplex families. This indicates differential mechanisms of genetic transmission of autism [6].

While it is clear that genetic factors play a significant role in the development of ASD, the exact mechanisms and interactions between genes and environment are complex and continue to be explored. Understanding these genetic contributions is key to unraveling the mystery behind the causes of autism spectrum disorder.

Environmental Influences

While the causes of autism spectrum disorder (ASD) are not completely understood, research indicates that both genetic and environmental factors contribute to its development. This section focuses on the impact of environmental influences on the risk of developing ASD.

Prenatal Risk Factors

Various prenatal factors have been identified as potential influences on the likelihood of developing autism. These include advanced parental age at the time of conception, maternal physical and mental health conditions, maternal prenatal medication use, and familial socioeconomic status.

For example, research has identified a significant association between increased risk of autism and paternal age older than or equal to 34 years. Maternal physical health conditions such as metabolic syndrome and viral infections during pregnancy, as well as maternal mental health conditions such as depression, anxiety, and stress, have also been linked to increased risk of autism in offspring. Maternal prenatal medication use, including the use of antiepileptic drugs and antidepressants, has been associated with increased risk of autism. Additionally, lower socioeconomic status in families has been found to be related to an increased risk of autism.

Certain difficulties during pregnancy, such as extreme prematurity, low birth weight, multiple pregnancies, and infections during pregnancy, have also been identified as environmental factors that might increase the risk of autism spectrum disorder.

Maternal Health and Autism

Maternal health plays a significant role in the risk of autism development. Research has found a link between mothers' diabetes and the risk of autism in children. Studies have shown that pregnant women with diabetes, including temporary diabetes, have a higher risk of delivering a child with autism compared to mothers without diabetes [7].

This connection between maternal health and autism underscores the importance of maintaining good health during pregnancy. It also highlights the need for further research into the complex interactions between genetics and environmental influences in the development of autism spectrum disorder.

The Interaction of Genes and Environment

In the quest to unravel the causes of Autism Spectrum Disorder (ASD), researchers have discovered that it's not simply a matter of genetics or environment, but rather a complex interplay between the two. This interaction, involving epigenetic mechanisms and environmental risk factors, plays a crucial role in the development of autism.

The Role of Epigenetics

Epigenetics, the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself, plays a significant role in ASD. Epigenetic mechanisms, such as DNA methylation, changes in histone proteins, and expression of noncoding RNAs, are integral to the interaction between environmental factors and gene expression in autism.

Exposure to harmful environmental factors can lead to changes in the expression of key genes involved in development, increasing the risk of autism. This complex interplay between genes and environment proves that the cause of autism is not merely genetic or environmental, but a sophisticated interplay of both.

Evidence of Gene-Environment Interplay

Studies indicate that certain prenatal risk factors for autism include advanced parental age, maternal physical and mental health, maternal prenatal medication use, and familial socioeconomic status.

For instance, there is a significant association between increased risk of autism and paternal age older than or equal to 34 years. Maternal physical health conditions such as metabolic syndrome and maternal viral infections during pregnancy, as well as maternal mental health conditions such as depression, anxiety, and stress, have also been linked to increased risk of autism in offspring.

The use of certain medications during pregnancy, including antiepileptic drugs and antidepressants, has also been associated with an increased risk of autism. Furthermore, families with lower socioeconomic status have been found to have an increased risk of autism.

Recent studies have even found a link between mothers' diabetes and the risk of autism in children. Pregnant women with diabetes, including temporary diabetes, have a higher risk of delivering a child with autism compared to mothers without diabetes.

These findings highlight the complex interaction between genetic and environmental factors in the development of ASD. While there are many unanswered questions surrounding the causes of autism, particularly how ASD is inherited from parents, it's clear that the interaction between genes and the environment plays a significant role in this mystery. This underscores the importance of ongoing research in this field to gain a better understanding of the causes of Autism Spectrum Disorder.

Early Diagnosis and Intervention

Understanding the causes of autism spectrum disorder is crucial, but equally important is recognizing the value of early diagnosis and intervention for individuals with ASD.

Importance of Early Detection

Early detection of ASD is key to providing the best possible outcomes for individuals with the disorder. Health care providers diagnose ASD by evaluating a person's behavior and development, and it can usually be reliably diagnosed by age 2. Starting treatments and services early can significantly improve a child's development and quality of life.

Early childhood providers can play an active role in supporting children with autism and other developmental disabilities. This includes tracking developmental milestones, communicating with parents, and being aware of community-based resources. Their involvement can significantly impact the lives of young children with ASD and their families.

Available Treatments and Services

Once ASD is diagnosed, treatment should begin as soon as possible. Treatment may involve a combination of medication to address specific symptoms, as well as behavioral, psychological, and educational interventions.

Research indicates that early intervention services can greatly improve a child's development. Certain medications and therapies can help manage symptoms related to autism spectrum disorder (ASD).

Awareness, acceptance, and appropriate supports are crucial for children with ASD to reach their incredible potential. Early care and education providers have the opportunity to make important contributions to the lives of these children by supporting and understanding the unique needs of each child with ASD.

From diagnosis to intervention, understanding and addressing the unique needs of individuals with ASD is critical. As we continue to unravel the causes of autism spectrum disorder, we can better support those affected by it and help them reach their full potential.

Autism Theories and Models

In the realm of research exploring the causes of autism spectrum disorder, several theories and models have been proposed to explain the complex nature of this condition. Among these are the diametric model and the extreme male brain theory, offering different perspectives on the underlying mechanisms that may contribute to the development of autism.

The Diametric Model

The diametric model of the mind, as detailed by Psychology Today, suggests that autism and psychosis exist on opposite ends of a spectrum. Autism is characterized by a limited ability to understand others' intentions and perspectives due to a literal, mechanistic understanding of the world. Conversely, psychosis involves the "overinterpretation" of others' intentions leading to paranoia and delusion.

This model is further supported by the imprinted brain theory, which proposes that autism results from greater paternal gene expression, while psychosis is suggested to result from greater maternal gene expression. Hence, the genes expressed from one parent can significantly impact a child's development.

One implication of the diametric model is that reduced mentalism in autism allows mechanistic cognitive skills to flourish, potentially leading to savant syndrome. Meanwhile, increased mentalism in individuals prone to psychosis can allow verbal and social skills to flourish.

Studies on brain imaging corroborate this model, showing that autism and psychosis have opposite effects on brain activity in regions governing mentalizing and reorienting attention, with decreased activity associated with autism and increased activity associated with psychosis.

The Extreme Male Brain Theory

The Extreme Male Brain Theory, proposed by psychologist Simon Baron-Cohen, offers a different viewpoint. As per this theory, autism has historically been diagnosed more frequently in men than women and is linked to certain cognitive domain variations by sex. It suggests that women generally excel at empathizing, while men excel at systemizing. In individuals with autism, the systemizing abilities are significantly heightened, forming the basis of the extreme male brain theory.

This theory, although controversial, has spurred further investigations into the role of gender and sex differences in autism, contributing to our evolving understanding of this complex disorder.

These theories and models, while providing valuable insights, do not offer a complete explanation of the causes of autism spectrum disorder. This underscores the complexity of autism and highlights the need for continued research to fully understand this condition.

References

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

‍[2]: https://www.nimh.nih.gov/health/topics/autism-spectrum-disorders-asd

‍[3]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9857540/

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

‍[5]: https://www.frontiersin.org/articles/10.3389/fncel.2019.00385

‍[6]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3513682/

‍[7]: https://www.cdc.gov/ncbddd/autism/facts.html

‍[8]: https://www.kennedykrieger.org/stories/interactive-autism-network-ian/theories-about-autism-causes

‍[9]: https://www.acf.hhs.gov/archive/ecd/child-health-development/asd

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