Key Facts

Intellectual disability involves significant limitations in both intellectual functioning and adaptive behaviour. It is a lifelong condition requiring tailored support and reasonable adjustments.

Epidemiology

Prevalence ~1-3% of the population (~1.5 million in England). Mild ID is most common (~85%). Life expectancy has increased but remains reduced compared to general population (median ~58 years overall; ~65 for mild ID).

Aetiology

Genetic causes (~50%):

• Chromosomal: Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), Turner syndrome, Klinefelter syndrome
• Single gene: Fragile X syndrome (most common inherited cause), PKU, tuberous sclerosis, Rett syndrome
• Microdeletion: 22q11.2 deletion (DiGeorge), Williams syndrome, Prader-Willi, Angelman syndrome

Acquired causes (~15%):

• Prenatal: TORCH infections, fetal alcohol spectrum disorder, teratogens
• Perinatal: Birth asphyxia, prematurity, neonatal hypoglycaemia
• Postnatal: Meningitis/encephalitis, head injury, non-accidental injury

Pathophysiology

• Varies by cause — chromosomal abnormalities affect multiple developmental pathways
• Down syndrome: Trisomy 21 → overexpression of chromosome 21 genes → amyloid precursor protein overexpression (early-onset Alzheimer's), cardiac malformations, thyroid dysfunction
• Fragile X: CGG trinucleotide repeat expansion → FMR1 silencing → loss of FMRP (important for synaptic plasticity)

Severity Levels

• Mild (IQ 50-69): Can often live independently with support; literate; may work in supported or open employment
• Moderate (IQ 35-49): Some self-care skills; supervised work possible; limited academic skills
• Severe (IQ 20-34): Requires substantial support; limited communication; basic self-care
• Profound (IQ <20): Requires continuous support; minimal communication; dependent for all care

Associated Features

• Communication difficulties (speech delay, limited language)
• Challenging behaviour (often communicative — pain, distress, unmet needs)
• Physical comorbidities: Epilepsy (20-50%), sensory impairment, dysphagia, constipation
• Mental health comorbidity: ~30-50% (anxiety, depression, psychosis, ADHD, ASD)

Red Flags

• Sudden behaviour change — consider pain, infection, constipation, medication side effects ('diagnostic overshadowing')
• Epilepsy — higher prevalence and more difficult to treat
• Dysphagia — aspiration pneumonia risk
• Safeguarding concerns — vulnerability to abuse/exploitation
• Regression of skills — consider dementia (especially in Down syndrome >40 years)

Bedside

• Cognitive assessment: WAIS-IV (adults), WISC-V (children) — IQ and profile
• Adaptive behaviour assessment: Vineland Adaptive Behaviour Scales, ABAS-3
• Physical examination: Dysmorphic features, neurological examination

Bloods

• TFTs: Especially in Down syndrome (hypothyroidism common)
• FBC: Baseline
• Genetic testing: Chromosomal microarray, karyotype; specific tests (Fragile X, PKU)

Imaging

• MRI brain: Structural abnormalities if cause unclear
• Echocardiogram: Down syndrome (congenital heart disease in ~50%)

Special Tests

• Hearing and vision assessment: High prevalence of sensory impairment
• EEG: If epilepsy suspected
• Newborn screening: PKU, CHT (identified on bloodspot)

Non-pharmacological

• Person-centred approach: Communication support (Makaton, PECS, easy-read materials)
• Positive behaviour support (PBS): First-line for challenging behaviour (NICE NG54); understand function of behaviour, proactive strategies
• Education: EHCP; special educational needs provision
• Supported living: Appropriate accommodation and support
• Annual health check: GP learning disability DES — physical health, medication review, screening
• Reasonable adjustments: Accessible healthcare, easy-read information, longer appointments

Pharmacological

• STOMP principles: Do not use psychotropic medication as first-line for challenging behaviour
• Only prescribe psychotropics for diagnosed mental health conditions or if behaviour poses significant risk AND non-pharmacological approaches have been tried
• If needed: Risperidone 0.25-2mg for aggression (short-term, specialist), SSRIs for depression/anxiety
• Regular medication review: STOMP-STAMP — at least annually
• Treat physical comorbidities: Epilepsy (lamotrigine, levetiracetam — avoid valproate in women), hypothyroidism, constipation

Referral Criteria

• Suspected ID — specialist assessment (paediatrics/psychology)
• Challenging behaviour — community learning disability team
• Mental health problems — specialist LD psychiatry
• Epilepsy — neurology (complex epilepsy in LD is common)
• Safeguarding concerns — safeguarding team

• Life expectancy: Reduced — overall ~58 years; mild ID ~65 years; severe/profound ~40-50 years
• Down syndrome: Life expectancy ~60 years (improved significantly); ~50% develop early-onset Alzheimer's disease by age 60
• Quality of life: Significantly improved with appropriate support, person-centred care, and community integration
• Mortality: Leading causes — respiratory disease, cardiac disease, epilepsy, cancer (often diagnosed late)
• LeDeR programme: Learning from Deaths reviews — identifies inequalities and avoidable deaths in people with LD

Common Genetic Causes

STOMP Principles