Biological Explanations for Autism

Although there is not a single clear explanation for why some people develop autism and others don't, psychological research has provided great insights into the factors that may be influencing the development of this disease. As usual in psychology, biological and environmental influences may be interacting and contributing to the development of autism.

Biological Explanations for Autism Biological Explanations for Autism

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Table of contents
    • First, the biological basis of autism will be explored.
    • Second, the explanation will look into the biological basis of autism.
    • Then, we will review the genetic causes of autism.
    • Moving on from this, the environmental causes of autism will be presented.
    • Then, the psychological factors of autism will be outlined.

    Autism, also referred to as Autism Spectrum Disorder (ASD), is a developmental disorder that often impacts social, emotional and communication skills.

    ASD may cause a person to perform repetitive behaviours, be highly revolved around routine and have difficulties with attention. A person with autism may have difficulties learning and can suffer from feeling overwhelmed for various reasons, including sensitivity to sensory experiences (e.g. loud noises).

    Some psychologists see a possible link between biological and environmental causes of autism. For example, they believe genetic and environmental factors, such as lack of play, can lead to autism. However, it is not yet clear whether autism is biological or environmental.

    Psychopathology, Biological Explanations for Autism, Picture of a child focussed on individual play, StudySmarter.Fig. 1. Picture of a child focussed on individual play.

    Biological Basis of Autism

    Autism is considered to have a biological basis. This is why an extensive amount of research has been devoted to explaining what these biological bases are. It is known that genetics play a role, but what is the key area in the brain where autism is reflected? Are there any other biological differences between autistic individuals and healthy individuals? There are the types of questions that those researching autism from the biological approach aim to answer.

    The biological explanations that are key for your exam will be explained next and include the following:

    1. The role of the amygdala

    2. Vitamin A

    3. Twin studies

    4. Fragile X gene

    5. Rett syndrome

    Autism Biology Research

    This section reviews the most influential biological papers exploring and explaining autism.

    The amygdala and autism

    Baron-Cohen et al. (2000) consider the biological approach to autism by focusing on the amygdala's role linked to social intelligence. They theorised that abnormalities with the amygdala might be associated with autism. They assessed autistic people using functional magnetic resonance imaging (fMRI) when they judged the expression of other people's eyes (inferring one's feelings from photos of eyes). They had to think about what the other person was thinking/feeling.

    Baron-Cohen et al. (2000) found that patients with autism did not activate the amygdala when attempting to understand or make mental judgements on the emotions in other people’s eyes. In contrast, the controls (people without autism) showed amygdala activity. This evidence suggests impairment of the amygdala is essential for explaining why those with autism lack social abilities, empathy, and the ability to make eye contact.

    Vitamin A and autism

    A lack of vitamin A impacting retinoid receptors in the brain is thought to cause symptoms of autism, such as lack of socialisation, eye contact, and sleep disruption. Megson (2000) supported this hypothesis by providing many children with autism vitamin A for two months. Abilities to socialise, language use and eye contact significantly improved after taking vitamin A for two months.

    One explanation explores the possibility that a lack of vitamin A during pregnancy can impact the development of the foetus in the womb, impacting abilities such as socialising, language use, and eye contact (Liu et al., 2021).

    Genetic Causes of Autism

    Genes may also be a cause of autism, or they may contribute to the development of the disorder.

    Twin studies and autism

    Rodier (2000) focused on genetic factors that contribute to autism. Rodier found in MZ twins (who share 100% of their DNA) that if one twin had autism, there was a 90% chance that the other twin would develop the disorder.

    The fragile X gene and autism

    Autism biological research supports the idea that genes with fragile X syndrome contribute to the development of autism. The FMR1 gene, responsible for causing fragile X syndrome, is responsible for 2–6% of cases of autism, therefore highlighting a potential link between the fragile X syndrome gene causing autism in some individuals.

    Rett syndrome and autism

    To support the theory of genetic causes of autism, Amir et al. (1999) found mutations in the MECP2 gene as the cause of Rett syndrome. Rett syndrome crosses over with features of autism with traits such as repetitive behaviours, regression, and motor abnormalities. It is on the autism spectrum.

    This mutation in the MECP2 gene accounts for around 80% of cases of Rett syndrome. Chao (2010) conducted a study to support these results and found that mice lacking the MECP2 gene developed behaviours similar to Rett's syndrome and autistic features such as repetitive behaviours.

    Rett syndrome affects girls predominantly, and a variant known as Preserved Speech Variant (PSV) is a milder version of Rett syndrome and showcases more autistic behaviours. Zappella et al. (2003) found that after studying two girls who fit into the PSV criteria, on a long follow-up on their behaviours, their initial behaviour followed the trajectory of the first few stages of Rett syndrome.

    However, they lost their autistic behaviours over the years and reached an IQ of 45. As a result, we cannot conclusively say the MECP2 gene is the cause of autism, just associated with it.

    MMR II vaccine and autism

    During the 1990s, the prevalence of autism dramatically increased (Ratajczak, 2011). Coincidentally, this coincided with marketing the second version of the measles, mumps, and rubella vaccine (MMR II.) This vaccine was contaminated with human tissue from the lung. It was suggested the increase in autism was due to this vaccine (Ratajczak, 2011).

    There are issues with this assumption. For example, Lievano et al. (2012) outlined that over 32 years of marketing the vaccine, there were 433 diagnoses of autism following vaccinations. Therefore, out of 575 million distributed doses, it is improbable that the MMR II vaccine is a potential cause of autism.

    This theory has so far been debunked. The author of the original paper claiming the link existed, Andrew Wakefield, was discredited and struck off the UK medical council.

    The prevalence of autism may also be down to better diagnostic criteria and techniques. People are far more aware of the disorder and are more likely to seek professional help. Medical doctors are also more aware of the disorder, explaining the rising diagnosis.

    Environmental Causes of Autism

    Studies looking into the interplay between nature and nurture in the development of autism have identified certain environmental factors that could be playing a role in the development of autism.

    Karimi et al. (2017) identified different environmental influences that impacted autism in their literature review. These were the following:

    1. Parental age: the literature suggested that an increased risk of developing autism was present when parents were 34 years old or older.
    2. Maternal physical health: having experienced an infection during pregnancy was also identified as a risk factor for developing autism.
    3. Maternal mental health: parental mental health was also associated with children's mental health. Therefore, if the mother had experienced a mental illness, the child was more likely to develop autism.
    4. Maternal medication use: the maternal intake of drugs has also been suggested to be a risk factor for children's development of autism. These studies investigated this link with various drugs, including antidepressants, psychiatric medication, pain killers and anti-epileptic drugs.
    5. Familial socio-economical status: the family's economic, social, educational and psychological well-being can also set children at a higher risk of developing autism. For example, stress and anxiety in the household can make children more prone to autism.

    Psychological Factors of Autism

    Psychologists define psychological factors as the functional characteristics that contribute to a person's development and well-being. There are certain psychological factors that autistic individuals present differently from healthy individuals. Among these factors, there are:

    • Lower academic performance as healthy individuals.
    • Impaired sensorimotor and perceptual abilities.
    • Different attention spans.
    • Difficulties in emotion perception.
    • Language development impairment.
    • Absence of Theory of Mind (ToM).

    Theory of mind or ToM refers to the ability to understand that just as one dies, others also know, want and believe things which may be different from our own.

    Cohen, Leslie and Frith (1985) developed a paradigm to test ToM on children. They had observed that individuals with autism were able to understand the mental states of others and thus developed a paradigm to research ToM.

    The paradigm consisted of presenting children with a specific situation and asking them to answer a question.

    In phase 1, Sally and Anne, two puppets, would come into the scene. The children would be told that Sally had a basket covered and that Anne had a box with a lid. The inside of the box and objects were, thus, not observable. Sally would put a marvel into her basket and leave the setting to go out to play.

    In phase 2, Anne would take the marvel while Sally was not present and put it in her box. Then, during Phase 3, Sally would return from playing and want her marvel. Then the child would be asked, where will Sally look for her marvel?

    If children had ToM, then they would understand that what they know and what Sally knows are different pieces of information, and therefore, Sally would look where she thought she left it; this is in her basket.

    Children who lack a ToM cannot distinguish between their knowledge and others' knowledge. This is, children would present false beliefs and answer that Sally will look in the box, which is what they know.

    After testing this task with healthy children, children with autism and children with Down's syndrome, they found that only 20% of children with autism presented ToM. Children with Down's Syndrome and healthy children showed similar performance.

    Biological Explanations for Autism - Key takeaways

    • Biological explanations of autism include the involvement of under-active amygdala activity in the brain and vitamin A deficiency.

    • Genetic explanations of autism explore how particular genes may lead to autism, including the Rett syndrome gene, fragile X gene and MECP2 gene.

    • In the 1990s, an increase in autism was linked to the vaccine MMR II. This theory has since been disproved.

    • The prevalence of autism may be down to better diagnostic criteria and techniques.


    1. Karahmadi, M., Karimi, P., Kamali, E., & Mousavi, S. (2017). Environmental factors influencing the risk of autism. Journal of Research in Medical Sciences, 22(1), 27.
    Frequently Asked Questions about Biological Explanations for Autism

    Does autism have a biological basis?

    Autism is thought to have a biological basis. The role of parts of the brain, such as the amygdala, has been considered as a possible explanation for autism. In addition, the role of vitamin A and its association with autism has also been considered. Genes also play a role, as MZ twins (twins who share 100% of their DNA) have a high concordance rate in autism diagnosis.

    Is autism biological or environmental?

    Autism is associated with both biological and environmental explanations. Some psychologists see a possible link between biological and environmental causes of autism. For example, they believe that both genetic factors and environmental factors such as lack of play can lead to autism. Overall, however, it is not yet clear whether autism is biological or environmental.

    What is the genetic cause of autism?

    The genetic cause of autism explores how autism can be passed down through genes. Several genes have been explored, including the Rett Syndrome gene, Fragile X gene, and MECP2 gene. Therefore, it is not known what exact genes may cause autism.

    Are there biological markers for autism?

    A potential biological marker for autism that has been explored in research is an underactive amygdala. An underactive amygdala has been linked to people with autism lacking social abilities, empathy, and the ability to make eye contact.

    What causes autism during pregnancy?

    One explanation explores the possibility that a lack of vitamin A during pregnancy can impact the development of the foetus in the womb, impacting abilities such as socialising, language use, and eye contact. 

    Test your knowledge with multiple choice flashcards

    Research found that in MZ twins (who share 100% of the DNA), if one twin has autism, there is a ___% chance that the other twin will develop the disorder.

    Is the following statement true or false: MMR II vaccine is the definite cause of autism?

    Is the following statement true or false: An underactive amygdala has been linked to explaining why those with autism lack social abilities, empathy and the ability to make eye contact?


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