27th October 2023

Autism Spectrum Disorders (ASD)

Classification

The contemporary diagnostic classification of ASD subsumes older diagnoses such as – Autism, autistic disorder, Asperger’s disorder, childhood disintegrative disorder, pervasive developmental disorder (not otherwise specified) under one diagnostic label with considerable heterogeneity in presentations.

The language of diagnosis

Given the aggregation of diagnoses in the latest classification systems, it is worth restating the importance of clarifying the preferred labelling language used when speaking to patients and their relatives – Independent of how a diagnosis is coded, some people may always think of themselves as being an ‘Aspie’, and these preferences should be honoured. The National Autistic Society also advises positive language, e.g. ‘autistic person’ or ‘person on the autism spectrum’; similarly, placing emphasis on challenges, strengths and supports as opposed to statements of ‘high or low functioning’ or ‘mild or severe forms of ASD’ (see autism.org.uk for more).

Presentation

For the diagnosis of ASD, individuals must experience difficulties in two main domains:

• Social and communication skills.
• Restrictive interests and repetitive behaviours.

Symptoms will be present in most by the age of 3 and must lead to significant impairment across multiple domains of daily living. They may also commonly co-occur with disorders of intellectual development or functional language impairments – presenting as difficulties in using language for instrumental purposes, e.g. to express personal needs, over and above the difficulties with communication detailed below:

Rett syndrome – A rare condition and remains a separate diagnosis in the ICD-11. Given its X-linked inheritance, it is almost unique to girls and is classically identified by a regression in well developing speech and social skills, loss of purposive hand motor skills (progression to hand wringing), deceleration in head growth and hyperventilation between 7-24 months of age. By four years old, there emerges truncal ataxia (able, poorly coordinated) or apraxia (inability for purposeful movement), choreoathetoid movements (paroxysmal, involuntary writhing), and severe ID.

Selective mutism – Diagnosed when a child can demonstrate language competency on par with development in one context (typically home) but consistently elects not to speak in other contexts (typically school) for a period of at least one month, interfering with normal engagement to an impairing level and not accounted for by other NDDs.

Assessment

Diagnosis is clarified through the process of:

Developmental history – Obtained from parents, including pre-and post-natal elements, as there are a number of environmental risk factors for ASD, such as neonatal hypoxia and having an older sibling with a diagnosis of ASD.

Direct observation – Ideally, in multiple contexts, including early years education and at home, it may be unstructured or structured. Structured assessments include the Autism diagnostic schedule-2ⁿᵈ edition (ADOS-2) and the Autism diagnostic interview-revised (ADI-R) (Leftort-Besnard et al., 2020). The ADOS-2 is an observational assessment that will vary depending on the age of the patient being assessed but might include playing some games with younger children or those without good verbal fluency or other activities and specific questions about school, feelings and friendships for those with more language capacities. It may be done with a parent present but not interacting with the child and will cover assessments of all the key traits of autism. Similarly, the ADI-R is an interview conducted with parents that focuses on three main domains – reciprocal social interaction, communication and language, and restricted and repetitive, stereotyped interests and behaviours and can be used to assess children from 18-months-old, as well as adults. Both may be used together or in isolation, depending on local constraints.

Explanatory models

Aside from the misguided and unhelpful theories – ‘raised by wolves, ‘refrigerator mothers’, ‘holy people’ – there have been many useful models proposed to explain the presentation and development of the symptoms of ASD:

• Theory of mind – Deficits in the ability to infer and utilise the understanding of one’s own and other’s mental states, such as beliefs, desires, preferences and pleasures.
• Social motivation theory – Argues for primary deficits in social orienting (i.e. face/gaze direction), social reward (i.e. pleasures derived from working collaboratively) and social maintenance (i.e. desires to maintain relationships through mimicry and emotional concealment.)
• Weak central coherence – Individuals with ASD have deficits in the ability to filter and integrate information in a global or broader context – to ‘see the bigger picture’ – due to a hyperconnectivity in the brain.
• Enhanced perceptual functioning – People with ASD possess heightened ‘locally oriented’ perceptions, i.e. are superior at observing, remembering and utilising specific details; this may be linked to the savant skills that are present in a few individuals with ASD.
• Executive dysfunction – Refers to problems in the processes underlying attention and action control.

Despite their supportive evidence bases and the useful explanations, these theories might provide to patients and their families, when used in isolation, they are limited in their explanatory power given they are largely non-developmental (often applying to single time points) and not (always) specific to ASD. Instead, it is likely that a complex series of mutually influencing developmental processes involving gene expression, synaptic signalling, brain activity, behaviour and the environment are responsible for the manifestations of ASD across the lifespan.

References

• National Autistic Society. How to talk about Autism. Available online at: https://www.autism.org.uk/what-we-do/help-and-support/how-to-talk-about-autism [Accessed March 2023]
• Chevallier, C., Kohls, G., Troiani, V., Brodkin, E. S., & Schultz, R. T. (2012). The social motivation theory of autism. Trends in cognitive sciences, 16(4), 231-239.
• Happé, F., & Frith, U. (2006). The weak coherence account: detail-focused cognitive style in autism spectrum disorders. Journal of autism and developmental disorders, 36(1), 5-25.
• Lefort-Besnard, J., Vogeley, K., Schilbach, L., Varoquaux, G., Thirion, B., Dumas, G., & Bzdok, D. (2020). Patterns of autism symptoms: hidden structure in the ADOS and ADI-R instruments. Translational Psychiatry, 10(1), 257.
• Lord, C., Elsabbagh, M., Baird, G., & Veenstra-Vanderweele, J. (2018). Autism spectrum disorder. The lancet, 392(10146), 508-520.
• Lord, C., Brugha, T. S., Charman, T., Cusack, J., Dumas, G., Frazier, T., … & Veenstra-VanderWeele, J. (2020). Autism spectrum disorder. Nature reviews Disease primers, 6(1), 1-23. Baron-Cohen, S. (2000). Theory of mind and autism: A review. International review of research in mental retardation, 23, 169-184.
• Mottron, L., Dawson, M., Soulières, I., Hubert, B., & Burack, J. (2006). Enhanced perceptual functioning in autism: An update, and eight principles of autistic perception. Journal of autism and developmental disorders, 36, 27-43.