27th October 2023

Developmental and Cognitive Psychopathology

Overview of Neurodevelopmental Disorders (NDDs)

Important classifications 

The ICD-11 states that NDDs encompass a spectrum of difficulties in the acquisition and execution of intellectual, motor, language or social functions, with onset in the developmental period before the age of 18 (World Health Organisation, 2019).

Three of the most clinically important diagnoses include intellectual disability (ID), autism spectrum disorders (ASD), and attention-deficit hyperactivity disorder (ADHD), which will be outlined in more detail in the subsequent sections. Other disorders include things like:

• Developmental learning disorders, e.g., reading, written expression, and mathematics impairments.
• Developmental speech or language disorders, e.g. speech sound, fluency (stuttering), language disorders.
• Developmental motor disorders, e.g. impairments acquisition and execution of coordinated motor skills, also includes some tic disorders.
• Stereotyped movement disorder, e.g. repetitive, apparently purposeless motor behaviour, e.g. hand flapping, rocking, head banging etc.

Shared components

Aetiology

There is significant co-occurrence of multiple NDDs across the levels of diagnosis, symptoms/problems, and underlying biology, including genetics, to the point where comorbidity is the ‘rule rather than the exception’.

For example, the overlap between ASD and ADHD is high:

• 22-83% of children with ASD have symptoms of ADHD, and 30-65% of children with ADHD have symptoms of ASD (Morris-Rosendahl & Crocq, 2022).
• Having a twin or sibling with ADHD or ASD puts other twins or siblings at a significantly greater likelihood of developing ASD, ADHD, and a host of other NDDs (Dewey, 2018).

However, if symptoms do not meet a diagnostic threshold (leading to a dual diagnosis), then vital clinical and research information risks being lost. Given the trait- or symptom-level overlap and subsequent blurring of boundaries between formal diagnoses, it might be appropriate to conceptualise NDDs as existing on a continuum of their own (Morris-Rosendahl & Crocq, 2022). Further study of the shared genetics, epigenetics and neurobiology, as called for by the research domain criteria (RDoC) project, is likely to make significant contributions to advancing this understanding and the subsequent classification systems.

Aside from biological predisposition, there are also thought to be some shared environmental factors for the development of NNDs, such as – prenatal exposure to alcohol or drugs, premature birth or low birth weight, and exposure to lead, mercury or certain components of plastics. The developmental origins of health and disease (DOHaD) hypothesis argues that NNDs are likely to be related to exposure to such environmental factors during critical periods of development, which subsequently affect genetics and body systems lifelong. Further research is required to elucidate the specifics of these relationships (Dewey, 2018).

Time course

For the vast majority of people, NNDs begin the developmental periods of early life and persist into adulthood; e.g. two thirds of children diagnosed with ADHD will have ongoing impairments into adulthood (RCPsych, 2023). Over time, those with NNDs are also at greater risk of exploitation and further psychiatric and physical health concerns. With early, specific intervention and ongoing support where necessary, there can be a significant reduction of disability for many people, highlighting the importance of timely and accurate assessment of needs.

Sex, gender and cultural factors

Perhaps unsurprisingly, NDDs are more commonly diagnosed in males than females, e.g. 4:1 in ASD, 2:1 in ADHD (Morris-Rosendahl & Crocq, 2022), although there is widespread variation in this. Presentation in females often varies significantly; e.g. females are more likely to present with inattentive symptoms of ADHD and may be better at ‘masking / camouflaging’ their symptoms of ASD (especially as people get older) and so go undiagnosed (Bölte et al., 2023). It is vital to consider the appropriateness of any formal testing (e.g. neuropsychological testing in ID) and the norms used for comparison, as performance might be affected by cultural biases and limitations of translation.

Neurodiversity

Although initially born from activists with ASD, the neurodiversity paradigm remains applicable to all NDDs, given their high heritability and frequent lifelong time courses. It is a relatively recent approach, centred on the fact that humans all vary in their neurological make up and subsequently how they process information: people with the most common sets of capacities are referred to as ‘neurotypical’, whilst those with broadly different ways of processing would come under the heading of ‘neurodiverse’.

In the context of disorders, it employs a social model for disability, i.e. disability arises not within the individual as the medical model would suggest but within the interaction between an individual’s capacities and their broader social context. One example of this relating to ASD might include failures for certain workplaces to sufficiently specify task requirements in ways that the autistic person might need. In this way, NNDs are seen as both natural variations (that, in a few instances, might also provide advantages) as well as disabilities. Consequently, there have been many useful insights, e.g. emphasising the importance of meaningful co-production in research, calling attention to support required by those with NNDs whilst striving for societal acceptance and emphasising the value of what people can bring. These perspectives also offer an important counterpoint to many interventions for things like ASD that continue to place a reduction of core symptoms as their goal, something which many of the community feel risks undermining efforts towards greater social provision (Den Houting, 2019).

References

• Bölte, S., Neufeld, J., Marschik, P. B., Williams, Z. J., Gallagher, L., & Lai, M. C. (2023). Sex and gender in neurodevelopmental conditions. Nature Reviews Neurology, 1-24.
• Den Houting, J. (2019). Neurodiversity: An insider’s perspective. Autism, 23(2), 271-273.
• Dewey, D. (2018). What is comorbidity, and why does it matter in neurodevelopmental disorders? Current Developmental Disorders Reports, 5, 235-242.
• Morris-Rosendahl, D. J., & Crocq, M. A. (2022). Neurodevelopmental disorders—the history and future of a diagnostic concept. Dialogues in clinical neuroscience.
• Royal College of Psychiatrists (2023) College Report CR235 ADHD in adults: Good practice guidance.
• World Health Organisation. (2019). Neurodevelopmental disorders. International statistical classification of diseases and related health problems (11th ed.).

Intellectual Disability (ID)

Classification

The evolution of classification for what is now commonly known as ID has developed significantly since it was first introduced into diagnostic manuals. Historical, underspecified terminology included terms such as simpleton and feeble-minded, have since progressed as greater efforts towards systemisation, including early IQ testing, yielded the historical classifications of moron (IQ 51-70), imbecile (IQ 26-50) and idiot (IQ 0-25).

These terms have developed further due to the ‘euphemistic treadmill’ – where a word becomes pejorative because it refers to something that attracts stigma, eventually leading to its replacement. In due course, this replacement might come to attract the same stigma, necessitating a further change in terminology. Change is often driven by activists working on behalf of the marginalised group, e.g. Rosa’s Law passed in 2010, which mandated the change of the term ‘mental retardation’ to ‘intellectual disability’ in the United States.

Advancements in descriptive psychopathology and testing have also helped clarify the diagnostic process, which now includes the consideration of:

• Standardised IQ and neuropsychological tests of domains such as working memory, processing speed, verbal comprehension and perceptual reasoning.
• Increasing specification of intellectual functioning and adaptive skills across different domains (see below).
• The inclusion of presentation and domain specific development across the lifespan.
• The inclusion of culture-, sex- and/or gender-related features.

The domains used by contemporary classification systems include:

• Conceptual – Communication, knowledge based tasks, e.g. problem solving, reading, writing, calculating.
• Social – Managing relationships, following rules and laws, avoiding victimisation.
• Practical – Skills for self care, work and recreation, finances, transport, health and safety, technology.

Contemporary diagnoses are made on the basis of a battery of standardised tests of intellectual and adaptive functioning (where possible) with scores compared to the mean, as these methods are more useful than IQ scores in isolation for understanding intellectual ability. These tests are performed in conjunction with clinical judgement of behaviours across the three domains highlighted.

Presentation

The following is a table depicting a breakdown of this in comparison to previous diagnostic categories and assessments:

Another relevant inclusion from the DSM-V is ‘Global developmental delay’, which can be diagnosed when individuals fail to meet expected developmental milestones across multiple domains of intellectual functioning and are unable to undergo systematic assessment, e.g. because they are too young (<5yrs). Individuals must be reassessed once capable of undergoing formal testing.

Specific aetiologies

As with many other neurodevelopmental disorders, the specific aetiology in the majority of cases remains unknown. However, there are a number of specific causes of ID to be aware of:

• Chromosomal and genetic conditions – Down syndrome, fragile X syndrome, phenylketonuria.
• Pregnancy and parturition related – Foetal alcohol spectrum disorder, maternal rubella or HIV infection, hypoxia during delivery.
• Problems in childhood – Infection (e.g. measles, meningitis), malnutrition (e.g. iodine deficiency), poisoning (e.g. lead or mercury), traumatic brain injury, asphyxia, stroke.
• Foetal alcohol spectrum disorder (FASD) – Describes the clinical features that can present in children from birth following maternal alcohol consumption during pregnancy, including facial anomalies (see picture); growth deficiency (weight/height <10th percentile); microcephaly; cognitive and behavioural impairments (e.g. problems with executive function, memory, attention, learning, language, visuospatial and motor processing etc.) Any alcohol intake at any time during pregnancy can lead to these features, especially above five units per day, but the greater the intake, the greater the risk. The prevalence is thought to be on par with ASD, perhaps unsurprising given that >40% of UK women consume some alcohol during pregnancy (Popova el al., 2023).

Image Source: Wikimedia Commons (2021). hoto of baby with FAS, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Photo_of_baby_with_FAS.jpg (Accessed on: 18 October 2023).

References

• Mentalhelp. History of stigmatizing names for intellectual disabilities continued. Available online at: https://www.mentalhelp.net/intellectual-disabilities/history-of-stigmatizing-names-for-intellectual-disabilities-continued/ [Accessed March 2023]
• American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders (4th ed.).
• American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.).
• Lee, K., Cascella, M., & Marwaha, R. (2019). Intellectual disability.
• Popova, S., Charness, M. E., Burd, L., Crawford, A., Hoyme, H. E., Mukherjee, R. A., … & Elliott, E. J. (2023). Fetal alcohol spectrum disorders. Nature Reviews Disease Primers, 9(1), 11.
• Stavrakantonaki, M., & Johnson, T. P. (2018). Effects of Rosa’s Law on Intellectual-Disability Reporting. Public Opinion Quarterly, 82(3), 593-604.
• World Health Organization. (1993). The ICD-10 classification of mental and behavioural disorders: Diagnostic criteria for research (7th ed.).
• World Health Organisation. (2019). Neurodevelopmental disorders. International statistical classification of diseases and related health problems (11th ed.).

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.

Attention Deficit Hyperactivity Disorder (ADHD)

Classification 

What was referred to in the ICD-10 as ‘hyperkinetic disorder’ is now classified under the ICD-11 and DSM-V as attention deficit hyperactivity disorder (ADHD).

The ICD-11 and DSM-V share many key diagnostic features, including:

• Symptoms of inattention and/or hyperactivity-impulsivity – either class may predominate.
• Symptoms must be present before 12 years.
• Persistent for at least 6 months.
• Present in 2 or more settings.

However, the DSM-V is more stringent with the number of symptoms, specifying the need for 6 or more in each domain to frequently be present to satisfy the diagnosis of a combined presentation.

The DSM-V also states that if assessed older than 17 years of age, then only 5 symptoms in each domain are required, and highlights the importance of symptoms not being solely attributable to oppositional behaviour or a failure to understand instructions, which might point more towards oppositional defiant disorder/conduct disorder or ID / ASD respectively (although does not of course rule out dual diagnosis).

Oppositional defiant disorder is another NDD that encompasses a profile of irritability, defiant and vindictive behaviour occurring at least once a week for at least 6 months. A child who frequently loses their temper, argues with or intentionally annoys authority figures and blames others for their mistakes should raise suspicions for ODD.

Conduct disorder (conduct dissocial disorder in the ICD-11) is similar to ODD and may develop from it but with a greater predominance of aggression, violence, destruction of property, deceitfulness and theft, and truancy for at least 6 months. It may begin as a child (<10yrs) or adolescent (>10yrs) and may remit or develop into enduring personality problems.

Assessment 

ADHD is a clinical diagnosis – based upon an interview and possible observation, but NICE guidelines state that rating scales such as the Conners’ rating scales and the Strengths and Difficulties questionnaire can be used as adjuncts (NICE, 2018). The Royal College of Psychiatrists also has a document that includes a list of rating scales and diagnostic interviews for adults, e.g. the Diagnostic interview for ADHD in adults (DIVA), which takes 1.5hrs to complete and includes a retrospective assessment of childhood behaviours too (Royal College of Psychiatrists, 2023).

References

• American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.).
• The National Institute for Health and Care Excellence (2018). Attention deficit hyperactivity disorder: diagnosis and management (NICE guideline NG87)
• Royal College of Psychiatrists (2023) College Report CR235 ADHD in adults: Good practice guidance
• World Health Organisation. (2019). Neurodevelopmental disorders. International statistical classification of diseases and related health problems (11th ed.).