The biology of autism

The Biology of Autism

Autism is complex and a constellation, meaning that there are just as many differences as similarities between autistic people. As such, anything written about autism may be true for some but not others. This article outlines research findings and clinical experiences linked to the biology (and neurology) of autism, though it must be stated that there is also much yet to be understood about the underlying biology of autism.

Is autism passed on through genes?

Research has shown that the majority (approximately 80 percent) of autistic people have likely inherited genes associated with autism. It is estimated that up to 1000 genes individually contribute in small and unique ways to shaping how a person thinks, learns, senses, and behaves. People have approximately 20,000 genes. They receive 50 percent of their genes from each of their parents, however, the number of genes originating from ancestors at the grandparent level and further back is not neatly divided in two with each generation.

What this means is that many people notice how autism runs in their families. For example, autism is more likely in twins, siblings and wider relatives. As such, if a parent carries a selection of the gene changes associated with autism, these can be passed on to their children. A small number of gene changes associated with autism does not make a person autistic by themselves, but the cumulative effect of a large number of genes associated with autism being present in the same individual can lead to that person being autistic.

An idea known as the broader autistic phenotype has attracted interest in recent years. This is linked to the reports from many autistic people and their family that similarities are noticed between their autism and aspects noticed in several relatives. For example, an aunt who may share in having a capacity to retain information easily, or a grandparent who was content in their own company, or an uncle who had an eye for detail, or a great grandparent who preferred to their familiar routines. The broader autistic phenotype represents autistic-like ways of thinking, sensing and behaving, but that in isolation do not cause daily challenges and impairment. An area this has been explored in is within the field of Science, Technology, Engineering and Mathematic (STEM). Relatives of autistic people are more likely to work in engineering, mathematics, technology and science-based roles. This has been understood by considering how people may have thinking styles that lend themselves to certain academic subjects and tasks. For example, lots of people working in STEM fields are found to have an ability to think in highly detailed and precise ways which can help them to notice subtle patterns in what they see and hear.

For 20 percent of autistic people, their autism originates from or is highly associated with a known medical condition or syndrome. This is where one, or just a few genetic differences are discovered. Examples supported in the literature include people with Fragile  Syndrome, Rett Syndrome, Williams Syndrome, Tuberous Sclerosis, Prader-Willi Syndrome, and Angelman Syndrome. Some autistic people also have an Intellectual Disability (previously called a Learning Disability), this is reported to range between 38 to 50 percent. Epilepsy is also more common in autistic people than non-autistic people. As autism awareness has increased and diagnostic criterion have been updated to reflect a wider range of autistic experiences, the rate of autistic people without an intellectual disability have increased. For some autistic people and their parents, genetic testing and genetic counselling is recommended following their autism assessment.

It is important to state that genes do not provide a 100 percent explanation, as there are lots of siblings and even identical twins (who share 100 percent of the same genes) where one is autistic, and the other is not. Autism assessments involve the person (or their parents/caregivers) providing background information, including on factors that have been found to increase the likelihood of a person being autistic. These include complications at birth associated with reduced blood supply/oxygen, advanced age of parents, maternal obesity and diabetes, and use of some medications (for example anti-epilepsy valproate) during stages of pregnancy.

A headline from the research findings is that autism is part of a person’s development from day one, that is during the pregnancy. Research concludes that autism cannot be developed from a life experience or situation. However, diagnostic changes in 2013 outlined how whilst some behaviours associated with autism are present in early childhood, it is common that for many people their autism does not become fully apparent until later in life, often when the social demands of life and living independently exceed their natural capacities to navigate situations and cope in sustainable ways over the long term.

Do autistic people have differences in their neurology?

Several aspects of biology associated with autism have been reported to show diversity and differences. One idea that has received research support is that some autistic children show differences in the number of brain cells (neurons) in their first four years of life. A natural process called ‘pruning’ occurs in these that involves some brain pathways becoming stronger through experiences, whilst other brain cells and pathways die off; the function of this is to aid efficiency in brain processing as messages travel across different parts of the brain. This is sometimes understood with the metaphor of walking paths and motorways. As messages in the brain travel on brain pathways that strengthen into well used roads and motorways, as opposed to having lots and lots of smaller walking paths that the brain uses to move information from one part to the next. Researchers have suggested that some autistic people experience a higher degree of brain activity in everyday life as there are more brain cells ‘firing’ with each when they are sensing, perceiving, thinking and reasoning with everyday life and interactions. Brain differences of this type in autistic and non-autistic children can sometimes be traced back to the first three months of development during pregnancy.

Early developmental differences in the neurobiology for some young autistic children include a reduced response in brain regions when others make eye contact with them, and less brain activity when in situations involving the seeking out and response in social interactions (for example, reacting to other’s speech and actions). Another overlap for many autistic people, more so than reported in non-autistic people, is in physical development (sometimes called motor skill development), for example developmental co-ordination disorder (also called dyspraxia) is more common for autistic people. A person’s way of processing sensory inputs (sights, sounds, tastes, smells, touch) can also be heightened for many autistic people, with the sensory input feeling more intense and not reducing as the person gets used to it. A way of understanding this is to think about how when going swimming in the sea, initially it feels incredibly cold but then a process of getting used to the water occurs (habituation) so that the water is no longer processed as feeling so cold.

Findings from neuropsychology also include differences between autistic and non-autistic people in two brain networks linked to our state of mind. The Default Mode Network (DMN) is a mode the brain enters when at rest and when there is no need to be deliberately focused on a task or activity. Many people refer to the Default Mode Network as when their mind can wander and daydream. In this mode, a person’s mind moves freely between different thoughts, ideas, self-reflections, and creativity. This can be useful for mulling over and processing things current in one’s life, as well as generating new possibilities and ideas; many people described this as a energy replenishing mode of being. The opposite mode the mind can be in is called the Task Positive Network (TPN), this is highly focused state typically used when needing to focus on external tasks and activities, or when having to consciously taking in information to then problem solve and make choices and decisions. This can be a tiring mode or can lead to a flow state being entered.

The DMN and TPN modes the mind can be in work alongside each other neatly in the sense that one mode is ‘on’ whilst the other is ‘off’. This allows for times of concentration and low distractibility, as well allowing  the mind to have ‘down time’ where it is not being asked to be highly focused on a specific idea, situation or problem. Brain scans have shown autistic people (as well as people with a diagnosis of attention deficit hyperactivity disorder) to have a different and not so straight forward pattern for their DMN or TPN’s. For example, both modes can be ‘on’ simultaneously and compete, so that it makes it harder for the person to remain focused and productive or to allow relaxing mind wandering to occur in ways that are energy replenishing. The other side of this is that a person can experience their thinking style as incredibly interesting, stimulating and high in creativity. For others, they report spending little time in the DMN, instead remain highly focused on situations, tasks and problem solving.

Another recent research finding about the biology of autism is how messages in the brain travel between areas close together in the brain and between regions that are further apart. An example of this incudes how it is common for some autistic people to have increased brain activity when processing language in both their left and right sides of their brain (brain hemispheres), whereas often non-autistic people process language more predominately in the left side of the brain. One explanation of this is that the main pathway between the sides of the brain (the corpus callosum) and long-range connectivity tracts can develop differently for some autistic people, a recent study found 17 percent less cells (density of brain cells in these tracts). The impact of this may be seen in some people in a range of thinking styles requiring the processing of sensing, analysing information and problem solving in moments of higher demand.

Researchers have reported that for a proportion of autistic people, more neurons (brain cells) are found in the prefrontal cortex. This area of the brain is often implicating in decision making, problem solving in new situations and process social behaviours. Sometimes having more neurons in a brain region means it can be ‘overactive’ which can be experienced by the person as a state of overload, confusion and general stress. Some autistic people have explained feeling a sense of alternating between highly focused thinking (flow states and hyperfocus) and being in a state of overload or ‘analysis paralysis’ when making decisions becomes challenging. Whilst not clearly reported in clinical neuropsychological research, some autistic people feel that their brain is working harder in daily life, which can leave them feel exhausted. Interestingly, these differences can be described a brain working too hard and focused, or working effortlessly.

Do autistic people have the same support needs?

The diversity seen in the underlying explanation for a person’s autism and how it shapes them as a person, means that there is great range of support needs within the autistic community. For some, it is linked to clear areas of impairment which cause a disability requiring very substantial support each day. For others, they explain that support in the form of reasonable adjustments ensure they can sustain a level of wellbeing that protects them from periods of mental health difficulties and autistic burnout. In an autism assessment, your level of support need is identified, using three levels described as requiring support (level one), requiring substantial support (level two), and requiring very substantial support (level three).

At DH Psychology we are committed to the ideas of neurodiversity and neurodivergence. Neurodiversity refers to the reality that everyone is different, and brains are included! By this, it needs to be known that there is a diversity in how people’s brain process information and function. Embracing this in communities, friendship groups, workplaces and schools can lead to an incredibly rewarding experience for all involved, as different perspectives and perceptions are able to be heard and valued. For around 20 percent of the population, differences in how their brain function can also be understood through a diagnosis such as autism, dyslexia or ADHD to name but just a few. Some people with these differences and diagnoses identify with the idea of neurodivergence. This is a way to describe people who think, learn, sense, perceive and behave in ways that feels markedly different from most non-autistic people in the population. Many autistic people find ways to connect with their personal areas of similarities and differences both with fellow autistic people and with non-autistic people.

Author

This article has been written by Dr Duncan Harris. Dr Harris is a clinical psychologist who has supported autistic children and adults for over 15 years. Alongside his professional doctorate, he holds a Masters in cognitive and neuropsychological research and has published several peer-reviewed academic articles in this field.

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