Intellectual disability (called intellectual developmental disorder in DSM-5-TR) has three parts:

1. Deficits in intellectual functioning — reasoning, problem solving, abstract thinking, learning — confirmed by clinical assessment and individually administered standardized intelligence testing (scores about 2 standard deviations below the mean, roughly 70 or below allowing for measurement error)
2. Deficits in adaptive functioning in conceptual, social, and practical areas (communication, self-care, safety, money, social judgment)
3. Onset during the developmental period

Severity (mild, moderate, severe, profound) is graded by adaptive functioning — the level of support needed — not by IQ alone. Most affected people have mild disability and can reach substantial independence with support.

Causes by timing

Down syndrome (trisomy 21)

• About 95% from nondisjunction (extra free chromosome 21; risk rises with maternal age); a small percentage from translocation (can be inherited — parental karyotype needed) or mosaicism (often milder)
• Causes mild to moderate intellectual disability, characteristic features, hypotonia, and a predictable set of medical conditions that require scheduled screening

Intellectual disability — clues by age

• Infancy: poor feeding, hypotonia, delayed social smile or sitting
• Toddler: delayed speech and language (often the first concern), delayed motor milestones
• School age: difficulty with academics, following multistep directions, and self-care skills compared with peers

Down syndrome — physical features

• Upslanting palpebral fissures, epicanthal folds, flat facial profile and nasal bridge, Brushfield spots on the iris
• Small ears, small mouth with protruding tongue, short neck with excess skin at the nape
• Single transverse palmar crease, short broad hands, fifth-finger clinodactyly, wide space between first and second toes
• Hypotonia and joint hypermobility; short stature

Fetal alcohol syndrome (FAS) — CDC diagnostic findings

• FAS is the most recognizable form of fetal alcohol spectrum disorder. CDC criteria need all three of the following:
  • Three facial features: smooth philtrum, thin upper lip (thin vermilion border), and small (short) palpebral fissures
  • Growth deficit: height or weight at or below the 10th percentile, before or after birth
  • Central nervous system abnormality: structural, neurologic, or functional (for example, global cognitive scores below the 3rd percentile, or scores below the 16th percentile in three functional areas)
• Prenatal alcohol exposure alone is not enough for the diagnosis, and the diagnosis can still be made when exposure is unknown if the other criteria are met
• Contrast with Down syndrome: FAS fissures are short, not upslanting

Associated conditions in Down syndrome

Pain in children with limited speech — rely on behavior (facial expression, crying, guarding, withdrawal, clinging, self-injury, changes in sleep or eating), physiologic signs, and above all the caregiver's knowledge of the child's usual pain behaviors. Use behavioral tools such as the revised FLACC or a noncommunicating children's pain checklist.

Intellectual disability

• Developmental surveillance at every well visit and standardized developmental screening at recommended ages
• Standardized intelligence tests (e.g., Wechsler scales) and adaptive behavior scales (e.g., Vineland) by qualified professionals
• Etiologic workup: chromosomal microarray and fragile X testing as first-tier genetic tests; metabolic tests if indicated; hearing and vision testing (sensory loss can mimic or worsen delay); lead level where exposure is possible; brain MRI when neurologic signs are present

Down syndrome

• Prenatal: screening (cell-free DNA, nuchal translucency with serum markers) versus diagnostic testing (chorionic villus sampling, amniocentesis)
• Postnatal: karyotype confirms trisomy 21 and identifies translocation

Health supervision in Down syndrome (AAP 2022)

• There is no cure for intellectual disability; management aims to maximize function, independence, and quality of life
• Early intervention from infancy: physical, occupational, and speech therapy; developmental stimulation; family coaching
• Individualized education (special education and related services, inclusive classrooms)
• Treat associated conditions: cardiac surgery (often AVSD repair in early infancy), thyroid replacement, hearing aids or ear tubes, glasses and cataract surgery, adenotonsillectomy or CPAP for sleep apnea
• Behavioral supports (positive behavior support); medications only for specific co-occurring conditions (e.g., ADHD, anxiety) with careful monitoring — children with intellectual disability may be more sensitive to side effects and less able to report them
• Transition planning in adolescence: adult health care, vocational training, supported living, guardianship alternatives such as supported decision-making

Listed in priority order.

1. Airway and cardiopulmonary safety — in infants with Down syndrome and heart disease, watch for heart failure (tachypnea, sweating with feeds, poor weight gain); aspiration risk with hypotonia; frequent respiratory infections — suction, humidity, upright positioning; screen for sleep apnea (snoring, pauses, restless sleep)
2. Protect the cervical spine — know myelopathy signs; careful neck positioning during anesthesia and procedures; report neck pain or gait change urgently
3. Assess pain and illness by observation — obtain vital signs and record observable behaviors, and ask caregivers how the child usually shows pain; do not rely on self-report scales the child cannot use
4. Feeding (Down syndrome)
   • Hypotonia and tongue protrusion weaken suck — support the chin and jaw, use an upright position, allow extra time and rest, burp often; breastfeeding is encouraged with support
   • Soft, spoon-fed solids placed toward the back of the tongue when ready; monitor weight
   • High-fiber foods and fluids for constipation; later, portion control and activity for obesity prevention
5. Hospital care for a child with intellectual disability
   • Keep familiar routines and objects; ask parents about communication methods, triggers, and calming strategies
   • Explain in short, concrete steps; show rather than tell; use pictures; allow extra time
   • Prepare for procedures one step at a time; minimize unnecessary stimuli
   • Parents are the experts — partner with them
6. Teaching self-care skills
   • Task analysis — break skills into small steps
   • Demonstrate, then practice with repetition; immediate positive reinforcement for each step
   • Consistency across home, school, and hospital
7. Medication administration — match method to understanding (visual schedules, demonstration); supervise doses; teach caregivers actions and side effects
8. Growth and development — use Down syndrome–specific growth charts where available; developmental stimulation based on the child's current level, not chronological age
9. Adolescence — puberty and hygiene education; sexuality education and protection from abuse and exploitation; social skills; independence in functional skills; transition to adult services

• At diagnosis: accept the parents' feelings, listen, and give information at their pace; balance medical facts with the child's strengths; offer parent support groups and early intervention referrals; avoid overwhelming them with everything at once
• Keep all scheduled screenings (heart, hearing, vision, thyroid, sleep); report signs of hypothyroidism (fatigue, weight gain, constipation, slowed growth), sleep apnea, and neck problems
• Signs of spinal cord compression needing urgent evaluation: neck pain, head tilt, change in walking, weakness, loss of bladder or bowel control
• Routine immunizations on schedule; annual influenza vaccine
• Healthy diet and daily physical activity to prevent obesity
• Teach skills through small steps, routines, and praise; avoid doing everything for the child
• Families with a translocation should receive genetic counseling about recurrence risk
• Siblings: include and inform them; watch for stress
• Help families plan for school supports, adult services, and long-term care arrangements

• Intellectual disability = intellectual deficits + adaptive deficits + onset in the developmental period; severity by adaptive functioning
• Down syndrome = most common genetic cause; fragile X = most common inherited cause; fetal alcohol = leading preventable cause
• FAS: smooth philtrum, thin upper lip, short palpebral fissures + growth at or below the 10th percentile + CNS abnormality
• Birth asphyxia is a perinatal (not prenatal) cause
• Down features: upslanting eyes, flat nasal bridge, protruding tongue, single palmar crease, hypotonia
• Most characteristic heart defect: AVSD (endocardial cushion defect); echocardiogram for every newborn with Down syndrome
• Screen hearing, thyroid (6 months, 12 months, yearly), eyes, and sleep apnea
• Atlantoaxial instability: no routine X-rays; watch for neck pain and gait change
• Feeding: support chin and jaw; allow time; hypotonia and tongue protrusion
• Teach with task analysis, repetition, and immediate praise; keep routines in hospital
• Pain in nonverbal children: observe behavior and ask caregivers