Intellectual developmental disorder — formative SAQs

SAQ 1 — Criteria, GDD and first-line evaluation (10 marks)

A 3-year-old is referred with delayed speech, delayed toilet training and inability to follow two-step commands. Hearing has not been formally assessed. There is no regression. The registrar asks whether this is “mild intellectual disability” and whether genetic testing can wait until school age. [1] [5]

Questions

1. Define intellectual developmental disorder using the three required elements, and explain why adaptive functioning is essential. (3 marks) [5]
2. Why is global developmental delay the better working label at age 3, and what actions must still happen now? (3 marks) [1]
3. Outline first-line aetiological and sensory evaluation priorities, including the role of chromosomal microarray. (4 marks) [1] [2]

Model answers

1. IDD requires significant deficits in intellectual functioning, significant deficits in adaptive functioning (conceptual, social, practical), and onset in the developmental period. Adaptive assessment is essential because intellectual scores and adaptive behaviour are related but not interchangeable; disability is defined by real-world function, not a lone IQ number. [5]
2. At age 3, formal cognitive testing is often unstable or invalid, so multi-domain delay is framed as GDD. You still open early intervention and education supports, complete hearing/vision pathways, take a full aetiological history/exam, and plan reassessment — you do not wait passively for school entry. [1]
3. Priorities: hearing and vision; chromosomal microarray as first-tier genetic testing for developmental disabilities; fragile X when indicated; phenotype-driven metabolic tests if red flags; consider broader sequencing later per ACMG CA/ID guidance and local access. Supports run in parallel with testing. [2] [3] [10]

SAQ 2 — School-age diagnosis, comorbidity and transition (10 marks)

An 8-year-old with long-standing multi-domain learning problems has formal testing consistent with intellectual developmental disorder of mild severity by adaptive support need. CMA is non-diagnostic. Teachers report exploitation by peers. Parents want “a tablet for focus” as the only plan. At 15 years the same young person still has no transition plan. [5] [17]

Questions

1. How do you distinguish mild IDD from specific learning disorder in this context? (2 marks) [5]
2. List four medical-home management domains beyond stimulant consideration. (4 marks) [16]
3. What transition actions should already be underway by mid-adolescence? (2 marks) [17]
4. State one prevalence anchor from Maulik and one genomics principle from Miller or Manickam. (2 marks) [4] [2] [3]

Model answers

1. Mild IDD shows intellectual limitation plus broad adaptive deficits across conceptual, social and practical life. Specific learning disorder is an academic skill deficit without global intellectual and adaptive disability in the IDD range. [5]
2. Any four: education adjustments and safety planning; speech/OT/psychology supports; hearing/vision/sleep/dental surveillance; behaviour and communication plans; mental health assessment; care coordination; family counselling; anti-overshadowing for new symptoms; revisit genetics if phenotype evolves. A stimulant is not the whole plan and may be irrelevant if ADHD criteria are absent. [16]
3. Transition: identify adult providers, teach condition knowledge at capacity-appropriate level, emergency plans, decision-making supports, sexual health, education/vocational planning — starting in mid-adolescence, not at the 18th birthday. [17]
4. Maulik: overall ID prevalence about 10.37/1000 in population-based meta-analysis. Miller: CMA first-tier for developmental disabilities/congenital anomalies. Manickam: ES/GS supported for pediatric CA/ID within ACMG guideline scope. [4] [2] [3]