Intellectual disability — assessment, classification and aetiological workup (MEQ)

(i) Criteria and severity. DSM-5-TR intellectual developmental disorder requires (A) deficits in intellectual functions confirmed clinically and with standardised testing when valid; (B) deficits in adaptive functioning limiting independence and social responsibility across environments; (C) onset during the developmental period. Severity (mild/moderate/severe/profound) is based primarily on adaptive functioning and support needs, not IQ band alone. This child has IQ in the mild range and clear adaptive deficits with developmental onset — consistent with mild ID if adaptive assessment confirms threshold.^[1][4]

(ii) Adaptive domains and measurement. Conceptual (language, academics, memory, self-direction), social (interpersonal skills, social judgment, naivety/gullibility), practical (self-care, safety, money, community use). Measure with standardised adaptive behaviour scales (e.g. Vineland, ABAS) plus multi-informant history across home and school — not unstructured impression alone.^[3][4]

(iii) Investigations. After clinical diagnosis and ensuring vision/hearing are addressed: physical/neurological examination; chromosomal microarray as first-tier genetic test; fragile X testing per evaluation pathways; escalate to exome/genome sequencing when first-tier uninformative or phenotype suggests high monogenic yield (landmark severe-ID exome evidence). Metabolic tests and MRI/EEG only for red flags (regression, consanguinity/metabolic clues, seizures, focal neurology) — not shotgun imaging in uncomplicated mild ID.^[1][2][5]

(iv) Differentials. Specific learning disorder: academic domain deficit with broader adaptive skills relatively preserved. ASD: requires social-communication pattern plus RRBs beyond developmental expectation — dual diagnosis allowed if both met. GDD: under-5 working label when IQ testing not yet reliable — not preferred at age 9 with valid testing. Borderline intellectual functioning: scores above ID intellectual threshold and/or adaptive criteria not met.^[1][4]

(v) Supports and mortality. No drug treats core ID. Deliver education plan, speech/OT as needed, disability funding supports (e.g. NDIS in Australia), carer support, and mental health screening without diagnostic overshadowing. CIPOLD (Heslop) showed elevated premature mortality with many deaths potentially avoidable — active health surveillance is mandatory systems practice.^[1][6]