Autism Causes: Genetic, Environmental and Neurobiological Factors Plus Gene-Environment Interaction
One of the key educational contributions to my development as a psychologist, counsellor and therapist was earning a master’s degree in psychology and mental health from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King’s College London. The programme was highly research-oriented, and one of the modules focused entirely on ADHD and autism. These areas of focus are highly relevant to my current work. As part of the course, I wrote several research summaries. The piece presented below is an extract from one of them, exploring the causes of autism.
Key Features of Autism Spectrum Disorder
Research suggests that the causes of autism are heterogeneous influences, which comprise genetic, environmental and neurobiological factors and gene-environment interaction. Autism spectrum disorder (ASD) is a spectrum of neurodevelopmental conditions with 1 in 68 children affected (CDCP, 2019). Impairments in social communication, limited interests and behavioural abnormalities, such as stereotypies and repetitions (Bourgeron, 2016), are the key features of autism. A diagnosis of ASD typically rests on behavioural indicators, without aetiology being taken into account (Baron-Cohen, 2002). However, research into aetiology has been extensively conducted to explore possible causes of autism.
Genetic Factors and Heritability of Autism
A growing body of research including meta-analytic studies suggests there is a solid genetic constituent in autism. Bourgeron (2016) reported the heritability estimates of ASD according to family and twin studies about 50%. However, Bai et al. (2019) estimated the heritability of ASD at 80% pointing out that the variation in autism incidence is mainly due to genetic reasons. Common variants represent most of the genetic part of autism. However, about 10% of individuals with autism, particularly those with intellectual incapacity, carry de novo copy-number variants or single nucleotide variants which affect ASD-related genes (Bourgeron, 2016).
Abnormalities in Brain Development
An increasing body of research suggests that abnormalities in brain development may cause ASD, and genetic factors may trigger this process (Williams et al., 2006). Magnetic resonance imaging has exposed numerous neurodevelopmental features which underpin symptoms of autism. The most consistent results point to increased growth of brain volume in children with autism about 2-4 years old (Ha et al., 2015).
Possible Environmentals Contributors into the Causes of Autism: Prenatal Processes
A substantial body of evidence points to various environmental influences which contribute to the aetiology of ASD. Several studies have established a strong association of maternal diet with autism, emphasising folic acid deficits (Surén et al., 2013). Two population-wide studies revealed that folic acid supplements taken close to conception are linked to a 40% reduction in the risk of ASD (Schmidt, Lyall, & Hertz-Picciotto, 2014). The strongest evidence of environmental contributions to autism comes from exposures to viral infections during pregnancy. Rubella is the greatest example (Amaral, 2017). Chess studied children affected by maternal rubella and revealed the striking prevalence of 741 autism cases per 10,000 children exposed to rubella. Amaral (2017) suggests that the cause of autism is prenatal, even if behavioural features are first noticed in later years.
Deficient Theory of Mind
Researchers also consider a deficient Theory of Mind (ToM), or impaired mentalising, as one of the possible contributors to autism. ToM refers to the ability to recognise and understand the desires, beliefs, goals and intentions of others. Individuals with ASD often show reduced activation in the brain’s mentalising system. The system comprises the superior temporal sulcus, medial prefrontal cortex, and temporal poles (Castelli, 2002).
Gene-Environment Interaction
Genes interacting with the environment can also be among the causes of autism. In the case of gene-environment interaction, particular environmental influences result in autism only in people with a specific genetic pattern (Amaral, 2017). The integrated approach considers the interactions between genes and the environmental prenatal or postnatal influences, both biological and psychosocial. The genotype can contain an alternative genetic form that will not be expressed if inhibited by factors facilitating genetic, environmental or epigenetic influences (Tordjman et al., 2014).
Male Preponderance
An important observation is that males appear to have a higher predisposition to autism than females (Baron-Cohen, 2002). The Extreme Male Brain theory of autism (Baron-Cohen, 2002) claims that female brains differ from male brains in functional and morphological characteristics. The theory asserts that the brain of individuals with autism is an extreme type of the male brain. Research associates this with raised foetal testosterone levels (Baron-Cohen, 2011).
What are the Causes of Autism: Conclusion
The research verdict on the causes of autism remains intricate. It seems that neither genetic nor environmental factors can cause autism individually but, in an interaction. Most likely this interaction happens prenatally, meaning that an individual with autism is born with this disorder. Research into epigenetic remodelling by environmental influences may facilitate the development of new treatment methods and prevention strategies. Investigating further the reasons for male preponderance could reveal more causes of ASD.
