PS11.1 | Intellectual Disability Disorder — Summary & Reflection

KEY TAKEAWAYS

Intellectual Disability Disorder (IDD) — classified under ICD-11 as Disorders of intellectual development — is diagnosed when there are co-existing deficits in intellectual functioning (IQ approximately ≤70), deficits in adaptive behaviour (conceptual, social, practical domains), and onset during the developmental period. DSM-5 grades severity based on adaptive functioning, not IQ score — the IQ bands (mild 50–69 to profound <20) are historical approximates only. Aetiology spans four categories: genetic/chromosomal (Down syndrome, Fragile X, PKU), prenatal non-genetic (TORCH infections, iodine deficiency, alcohol, valproate), perinatal (birth asphyxia, kernicterus, prematurity), and postnatal (meningitis, lead). Assessment requires standardised intelligence testing, adaptive behaviour evaluation (Vineland Scales), and developmental history. Management is multidisciplinary: early intensive intervention, special education, speech/OT/PT, behaviour support, family psychoeducation, and treatment of co-morbidities. Prevention — neonatal screening, iodine supplementation, rubella vaccination, skilled birth attendance — is a primary-care responsibility. Differential diagnosis includes ASD, specific learning disorder, and dementia; co-occurrence of ASD and IDD requires both diagnoses when criteria are met.

REFLECT

A 2-year-old girl is brought to your primary health centre because she has not started speaking. She was born at term after an uneventful delivery but has not walked independently and has poor muscle tone. Her mother reports that her husband's family 'has had children like this before'. Reflect on: (1) What aetiological investigation would you prioritise, and how does the family history of similar cases change your thinking about chromosomal vs monogenic inheritance? (2) How would you counsel this family about their daughter's likely future needs while remaining sensitive to cultural stigma around intellectual disability in your community? (3) What preventive advice would you offer regarding future pregnancies? Write a brief reflective note on how your approach to this family interaction would be informed by the principles you have learned today.