Understanding Intellectual Disability: IQ Scores and Adaptive Functioning

Intellectual Disability (ID) (formerly "mental retardation") is a neurodevelopmental disorder characterized by deficits in intellectual and adaptive functioning, onset before age 18.

Diagnostic Criteria (DSM-5 / ICD-11)

1. Intellectual deficits: IQ ≤70 (typically ≤75 with clinical judgment) on standardized, individually administered test (e.g., WISC-V, WAIS-IV, Stanford-Binet).
2. Adaptive deficits: Impaired functioning in ≥1 domain vs. age/cultural expectations:
   • Conceptual: language, literacy, math, reasoning, memory.
   • Social: empathy, friendship, judgment, gullibility.
   • Practical: self-care, money, recreation, work, safety.
3. Onset during developmental period.

Severity Specifiers (Based on Adaptive Function)

Severity	IQ Range	Adaptive Profile
Mild	50–70	May achieve academic skills to ~6th grade; independent living with support; employment possible.
Moderate	35–50	Basic self-care, communication; supervised living/work.
Severe	20–35	Limited conceptual; extensive daily support; communication basic.
Profound	<20	Very limited understanding; total care; sensorimotor communication.

Borderline Intellectual Functioning

IQ 71–85. Not ID, but increased risk for learning difficulties, mental health issues, social vulnerability. May benefit from support services.

Etiology

Genetic (Down, Fragile X, Rett), prenatal (alcohol, infections), perinatal (hypoxia, prematurity), postnatal (trauma, lead, malnutrition), often multifactorial/unknown.

Supports & Rights

IDEA (education), ADA (accommodations), SSI/Medicaid, supported decision-making (alternatives to guardianship). Person-centered planning maximizes autonomy.