Overview
This lecture covers two childhood neurodevelopmental disorders: Intellectual (Developmental) Disability (IDD, He Tamaiti Haua) and Autism Spectrum Disorder (ASD, Takiwātanga). For each it works through the DSM-V diagnostic criteria, presentation, risk factors, prevalence/incidence, and comorbidities, then closes with shared themes of respectful clinical practice, diagnostic overshadowing, and assessment/intervention in the New Zealand context, including a worked exam-style case (Hailey) applying the ASD criteria.
Intellectual (Developmental) Disability: definition and diagnostic criteria
- IDD is grouped in the DSM-V neurodevelopmental disorders.
- It reflects global difficulties in information processing (though the profile of difficulties can still vary between individuals).
- Distinct from a specific learning disability.
- Distinct from the effects of illness or injury, which are classed as a neurocognitive disorder.
DSM-V diagnostic criteria — all three must be met:
- A. Deficits in intellectual functioning: reasoning, problem solving, planning, learning, judgement.
- B. Deficits in adaptive functioning that cause failure to meet developmental/social standards for personal independence and social responsibility, affecting communication, social participation, and independent living, across multiple environments (e.g. home, school, community).
- Onset of the intellectual and adaptive deficits during the developmental period.
IDD: presentation, risk factors and epidemiology
- Not always obvious on appearance. Early recognition is more likely when there is severe impairment, impairment across multiple domains of function (e.g. delayed milestones), or the presence of multiple risk factors.
- Risk factors fall into three groups:
- Adverse postnatal environment: deprivation of nurturance and other stimulation.
- Pregnancy and perinatal problems: fetal malnutrition, prematurity, hypoxia, viral and other infections, trauma.
- General medical conditions: seizure disorders, infections (e.g. measles).
- Prevalence: estimated 1–3%, more common in males than females.
- Etiology is undetermined in 30–40% of cases.
- Strong genetic/hereditary component: over 500 genetic disorders are associated with ID, including Down syndrome, Fragile X syndrome, and Tuberous sclerosis.
- Adverse prenatal environment: Fetal alcohol syndrome, lead poisoning, maternal infection.
- Pervasive developmental disorders are also listed among the etiological categories.
- Difficulties associated with IDD arise from a complex interaction across four domains:
- Cognitive: attention, concentration, persistence, problem-solving/inflexibility, multi-tasking (working memory), organisation.
- Behavioural: social difficulties, passive/withdrawn vs disruptive/oppositional presentation, slow/difficulty following instructions, difficulty staying on task, ability to work independently and show initiative, sensory sensitivity, repetitive behaviours.
- Developmental: delayed milestones, fine and gross motor coordination difficulties, language delays.
- Systems: discrimination, reduced opportunities, parental stress, relationship discord, financial stress, anxiety about the future.
Respect, dignity and comorbidity in IDD
- Important to balance developmental level with dignity: a 25-year-old with a “mental age” of 15 is NOT the same as an actual 15-year-old typically developing person.
The lecture includes an embedded video on dignity and respect at this point in the slides; its content could not be transcribed from the rendered slide image.
- Comorbidity is very common (range 10–70%).
- The type of comorbidity varies with severity of IQ impairment: depression, anxiety and antisocial presentations are more common in those with higher IQ; psychotic disorders and autism spectrum disorder are more likely at lower IQ levels.
- Challenging behaviour is common and may reflect underlying emotional problems.
- Maltreatment is common, with an unclear relationship to IDD (it may be either a cause or an outcome).
- Clinicians should beware diagnostic overshadowing — attributing new symptoms to the existing disability rather than assessing them independently.
Autism Spectrum Disorder: definition and three domains
- Takiwātanga/ASD is a neurodevelopmental condition that leads to cognitive, social and sensory processing differences that influence a person’s understanding of, and interaction with, the world.
- It is neuro-developmental: not an illness, but a neurological difference present from childhood throughout the lifespan.
- Three domains of ASD symptomatology: social, communication, and repetitive and restrictive behaviour.
ASD: DSM-V criteria and differential diagnosis
DSM-V criteria:
- A. Persistent deficits in social communication and social interaction across multiple contexts, with symptoms from all three of: social-emotional reciprocity, nonverbal communicative behaviours, and relationships.
- B. Restricted/repetitive behaviours, interests or activities (at least 2 present).
- C. Symptoms must be present in early childhood, though they may not become fully manifest until social demands exceed the person’s limited capacities.
- D. Clinically significant impairment.
Differential diagnosis for ASD:
- Social Communication Disorder — pragmatic difficulties with language and communication; has the social and language difficulties of ASD but without the restricted and repetitive behaviours required for an ASD diagnosis.
- Intellectual Developmental Disorder.
- Language disorders.
- Obsessive Compulsive Disorder.
- Anxiety.
- Normative social difficulties.
- Normative personality variances.
Applying the ASD criteria: case example (Hailey)
Exam-style case: Hailey, a 7-year-old girl, has never had friendships at early childhood centre or school; at birthday parties she plays alone and does not respond to invitations to join group activities; she talked later than other children and it was unclear whether she understood others, as she has always been difficult to get eye contact from; her parents struggle to know how she is feeling as she shows little overt emotion.
The table summarising this case in the slides is headed "Jacob" even though the case is named "Hailey" throughout; the inconsistency is in the original slide and is not resolved here.
Model answer:
- The three domains are social, communication, and restricted and repetitive behaviours.
- Social: disinterest in playing with other children, no friendships — deficits in developing, maintaining and understanding relationships.
- Communication/language: nonverbal communication difficulties (poor or abnormal eye contact, flat affect/lack of facial expressions), delayed language development.
- To confirm the diagnosis, further information is needed on: social-emotional reciprocity (to fully meet Criterion A), evidence of at least 2 restricted/repetitive behaviours (Criterion B), evidence the features were present from early childhood, evidence of clinically significant impact, and confirmation that the presentation is not better explained by IDD or another developmental disorder.
ASD: incidence and risk factors
- Incidence rates vary across time and sources, and appear to be increasing.
- NZ Ministry of Health figures: 1.2% in 2014 rising to 2.2% in 2017 — it is unclear whether this reflects a true rise in incidence or improved detection.
- More common in males, at a ratio of about 4:1 overall.
- Ratio varies with intellectual disability status: 5–16:1 when there is no ID, but around 1:2 (more females) when ID is severe.
- Females are often diagnosed later.
- Risk factors:
- Family history: risk of autism in siblings is around 50 times that of the general population; high concordance in monozygotic twins; recurs within families at a rate of 3–6%.
- Maternal age.
- Paternal age.
- Perinatal complications (e.g. hypoxia).
- Vaccination: NO link — despite claims made in the late 1990s, there is no evidence linking the MMR vaccine to ASD.
ASD: comorbidities, other difficulties and outcomes
Common comorbidities: IDD (50–80%), specific learning disorder, speech/language disorders, anxiety, ADHD, mood disorders, tic disorders, seizure disorders.
Other associated difficulties:
- Sleep disturbances, particularly with sleep onset.
- Eating difficulties: restricted range of foods, aversion to certain textures.
- Emotional regulation: intense mood, difficult to soothe.
Outcomes: more positive outcomes are associated with higher IQ, language skills (meaningful speech before age 5), and early identification and intervention.
"If you have met one person with autism, you have met one person with autism" (Autism NZ website) — used in the lecture to emphasise the heterogeneity of presentation across individuals with ASD.
Assessment and clinical management of IDD and ASD
- IDD and ASD assessment: refer for specialist assessment to establish diagnosis; treat other concerns as you would for typically developing children, adapting interaction style as needed; beware diagnostic overshadowing and remember the high rate of comorbidity — actively assess for it.
- Things to consider clinically:
- Routine and sensory issues need to be worked through with the patient.
- Consider how to prepare the patient for unfamiliar places and experiences, e.g. using Social Stories.
- Use the patient’s special interests as a way to build rapport.
- May need more structure in questions and to check in on shared understanding, because of Theory of Mind difficulties and literal interpretation of language (e.g. the idiom “it’s raining cats and dogs” can cause difficulty).
- Intervention in NZ: a study (Kasilingam et al., 2019) found children with ASD receive much less intervention than Ministry of Health guidelines recommend.
- Recommended: 60–100 hours/month.
- Actual: 8.7 hours/month.
- Families would like 19 hours/month.
- Families are getting 2 types of support but would like 7, and would particularly like more behavioural support.
- Resources and supports named in the lecture: Altogether Autism Takiwātanga, Autism NZ (“Every step together”), and the Autism Intervention Trust.
Self-test
- Define intellectual (developmental) disability and describe how it differs from a specific learning disability and from a neurocognitive disorder.
- List the three DSM-V criteria required to diagnose IDD, including the domains assessed under intellectual functioning and under adaptive functioning.
- What features make an intellectual disability more likely to be recognised early?
- List the three broad categories of risk factors for IDD and give one example from each.
- What is the estimated prevalence of IDD, and in what proportion of cases is the etiology undetermined?
- Name three genetic conditions associated with intellectual disability mentioned in the lecture.
- Explain why balancing “mental age” with dignity matters when working with an adult with IDD, using the example given in the lecture.
- Describe how the type of comorbidity in IDD varies with severity of IQ impairment, and define “diagnostic overshadowing”.
- Define Autism Spectrum Disorder (Takiwātanga) and state whether it is classified as an illness.
- List the three domains of ASD symptomatology.
- Describe the DSM-V criteria (A–D) for diagnosing ASD.
- Distinguish ASD from Social Communication Disorder.
- Vignette: Hailey, a 7-year-old, has never formed friendships, plays alone at parties, has delayed language, avoids eye contact and shows little overt emotion. Which ASD domains do her features fall into, and what further information would you need to confirm the diagnosis?
- What do NZ Ministry of Health figures show about ASD incidence between 2014 and 2017, and what uncertainty is noted about the cause of the change?
- Describe how the male:female ratio in ASD diagnosis varies with severity of intellectual disability, and what is noted about the timing of diagnosis in females?
- List three risk factors for ASD, and state what the lecture concludes about a vaccination link.
- List the common comorbidities of ASD, and the three other associated difficulties covered (sleep, eating, emotional regulation).
- What three factors are associated with more positive outcomes in ASD?
- Describe two clinical strategies for interacting with a child with ASD, and explain what “Theory of Mind” difficulties mean in this context.
- What did Kasilingam et al. (2019) find about the gap between recommended and actual monthly intervention hours for children with ASD in NZ?
Answers
Reveal answers
- IDD is a DSM-V neurodevelopmental disorder reflecting global difficulties in information processing (though profile can vary). It is distinct from a specific learning disability, and distinct from a neurocognitive disorder, which results from the effects of illness or injury rather than a developmental global processing deficit.
- A: deficits in intellectual functioning (reasoning, problem solving, planning, learning, judgement); B: deficits in adaptive functioning affecting communication, social participation and independent living, across multiple environments, causing failure to meet developmental/social standards for independence and responsibility; onset of both during the developmental period.
- Severe impairment, impairment across multiple domains of function (e.g. delayed milestones), and presence of multiple risk factors.
- Adverse postnatal environment (e.g. deprivation of nurturance/stimulation); pregnancy and perinatal problems (e.g. fetal malnutrition, prematurity, hypoxia, infections, trauma); general medical conditions (e.g. seizure disorders, infections such as measles).
- Estimated 1–3% prevalence, more common in males; etiology is undetermined in 30–40% of cases.
- Down syndrome, Fragile-X syndrome, and tuberous sclerosis (of over 500 genetic disorders associated with ID).
- A person’s chronological age and life experience remain their own even if their functional/“mental age” is lower — a 25-year-old with a mental age of 15 is not the same as an actual 15-year-old typically developing person, so dignity appropriate to their real age and life stage must be maintained alongside adapting to their developmental level.
- Depression, anxiety and antisocial presentations are more common with higher IQ; psychotic disorders and ASD are more likely with lower IQ. Diagnostic overshadowing is attributing new symptoms or behaviours to the person’s known disability rather than assessing them as a possible separate/comorbid problem.
- ASD is a neurodevelopmental condition causing cognitive, social and sensory processing differences that affect a person’s understanding of and interaction with the world. It is not an illness — it is a neurological difference present from childhood throughout the lifespan.
- Social, communication, and repetitive and restrictive behaviour.
- A: persistent deficits in social communication/interaction across multiple contexts, with symptoms from all of social-emotional reciprocity, nonverbal communicative behaviours, and relationships; B: restricted/repetitive behaviours, interests or activities, at least 2 present; C: symptoms present in early childhood (may not fully manifest until social demands exceed capacity); D: clinically significant impairment.
- Social Communication Disorder involves pragmatic language/communication difficulties with the same social and language difficulties seen in ASD, but without the restricted and repetitive behaviours required for an ASD diagnosis.
- Social domain: disinterest in playing with other children, no friendships (deficits in developing/maintaining/understanding relationships). Communication domain: nonverbal communication difficulties (poor eye contact, flat affect/lack of facial expression), delayed language development. Further information needed: evidence on social-emotional reciprocity, evidence of at least 2 restricted/repetitive behaviours, evidence the features were present from early childhood, evidence of clinically significant impairment, and confirmation the presentation is not better explained by IDD or another developmental disorder.
- Reported ASD prevalence rose from 1.2% in 2014 to 2.2% in 2017; it is unclear whether this reflects a true increase in incidence or improved detection.
- Overall male:female ratio is about 4:1; the ratio widens to 5–16:1 when there is no accompanying intellectual disability, but narrows to around 1:2 (more females) when ID is severe. Females are often diagnosed later than males.
- Family history (about 50x sibling risk vs general population, high monozygotic twin concordance, 3–6% family recurrence rate), maternal age, paternal age, and perinatal complications (e.g. hypoxia) are risk factors. There is no evidence of a link to the MMR vaccine, despite claims made in the late 1990s.
- Comorbidities: IDD (50–80%), specific learning disorder, speech/language disorders, anxiety, ADHD, mood disorders, tic disorders, seizure disorders. Other difficulties: sleep disturbances (particularly sleep onset), eating difficulties (restricted range of foods, texture aversion), and emotional regulation difficulties (intense mood, difficult to soothe).
- Higher IQ, language skills (meaningful speech before age 5), and early identification and intervention.
- Strategies include preparing the child for unfamiliar places/experiences (e.g. using Social Stories) and using the child’s special interests to build rapport; also providing more structure in questions and checking shared understanding. Theory of Mind difficulties mean the child may struggle to infer others’ mental states/perspectives, and may also interpret language literally (e.g. not understanding the idiom “it’s raining cats and dogs”).
- Recommended intervention is 60–100 hours/month, but actual delivered intervention was only 8.7 hours/month; families would like 19 hours/month, are receiving 2 types of support but would like 7, and would particularly like more behavioural support.