07 · Intellectual disability, autism and adult ADHD

7.1 Intellectual disability: definition and severity

Intellectual disability involves significant limitations in intellectual and adaptive functioning, beginning during development. ICD-11 calls these disorders of intellectual development; UK services usually use learning disability. A specific learning difficulty such as dyslexia does not imply global intellectual impairment.

Adaptive functioning covers conceptual abilities, social understanding and practical daily skills. It describes support needs in the person's environment. IQ alone cannot establish diagnosis, everyday abilities or decision-making capacity.

ICD-11 considers both intellectual and adaptive function. Severe and profound disability are distinguished by adaptive functioning because intelligence testing is limited at the lower end. A child's “mental age” is not an appropriate description of an adult. Skills are uneven; adult experience, identity and rights remain.

7.2 Diagnostic overshadowing and altered presentation

Diagnostic overshadowing means explaining a new symptom by the disability and missing another disorder.

Depression may appear as reduced enjoyment, withdrawal, sleep/appetite change, irritability, crying, self-injury or increased dependence. A persistent change across several areas matters more than one behaviour. Limited speech reduces the sensitivity of ordinary symptom interviews; it does not rule out depression, psychosis or suicidal thinking.

Self-talk or autistic repetition may resemble psychosis. Establish an acquired psychotic syndrome against the person's communication style and baseline. Excitement alone is not mania; a preference for routine is not automatically OCD.

7.3 Behaviour that challenges: causes and mechanisms

The term describes behaviour whose intensity, frequency or duration causes substantial difficulty or danger. It is not a diagnosis. Aggression, biting, head-banging, refusal and withdrawal can have several causes together.

Constipation may cause overflow soiling: loose stool does not exclude impaction. Pain, reduced intake and vomiting can accompany severe constipation. Epilepsy is more common with intellectual disability, especially greater impairment. Postictal agitation is possible; sustained purposeful aggression should not casually be attributed to “temporal lobe epilepsy”.

Functional assessment

Antecedent → behaviour → consequence identifies what precedes and maintains behaviour. Possible functions include escaping an overwhelming demand, gaining attention/an activity, or sensory reinforcement. A consequence is reinforcing if it increases future behaviour, regardless of staff intention.

Positive behavioural support changes the environment, teaches alternatives and develops consistent responses around the person's needs. Reducing visible behaviour alone is insufficient, and the formulation does not replace diagnosis of illness.

Antipsychotics and STOMP

Consider antipsychotics only if other interventions have failed within an agreed period, treatment of contributing illness has not helped, or risk is very severe. Combine them with psychological/environmental interventions, a defined target and specialist monitoring. Review at three–four weeks; stop at six weeks without evidence of benefit. Benefit still requires ongoing review and a stopping strategy.

Sedation is not proof that the cause has improved. Harms include weight/metabolic effects, hyperprolactinaemia, constipation, falls and movement disorders. STOMP addresses inappropriate overmedication in learning disability/autism through appropriate indications, review and deprescribing. It does not mean withholding effective treatment for established illness.

7.4 Down syndrome: acquired decline is not inevitable “ageing”

Why Alzheimer's risk rises

An extra chromosome 21 usually increases dosage of APP, the amyloid precursor protein gene. This contributes to early Alzheimer pathology, but pathology may precede clinical dementia by years. Risk rises with age; the age of onset varies.

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Diagnose decline from the individual's own baseline. A low ordinary cognitive-screen score cannot establish dementia. Early changes may be apathy, reduced initiative, altered social behaviour, extra prompting or lost skills; clearer memory/orientation problems may follow.

Hearing/visual problems, thyroid disease, sleep apnoea, congenital cardiac disease and seizures also affect behaviour and prescribing.

New epilepsy

New seizures in a middle-aged adult with Down syndrome may accompany Alzheimer's. Late-onset myoclonic epilepsy causes brief jerks, sometimes on waking, and may include generalised tonic–clonic seizures; do not assume temporal lobe epilepsy. Seizures can impair functioning, and antiseizure treatment may add sedation or behavioural effects. More than one explanation can be correct.

7.5 Genetics, pregnancy and parenting

There is no single inheritance risk for “learning disability”. Causes include chromosomal/single-gene disorders, prenatal exposures, perinatal injury, infection and other developmental insults; sometimes none is identified. Recurrence estimates depend on the cause, pedigree and genomic assessment.

Down syndrome usually follows nondisjunction; a minority involve translocation or mosaicism. A balanced parental translocation changes recurrence risk, so the diagnostic label alone is insufficient.

Fragile X

FMR1 CGG-repeat expansion on the X chromosome is an important inherited cause. Features include learning/social-communication difficulties, anxiety, hyperactivity, long face, prominent ears, joint laxity and macro-orchidism after puberty. Males are often more severely affected; female expression varies.

Premutation alleles have different consequences, including fragile X-associated tremor/ataxia and primary ovarian insufficiency. Counselling must account for both transmission and repeat expansion.

Parenting and reproductive decisions

Intellectual disability does not establish inability to parent. Assess skills, circumstances, safety and available support, allowing adapted teaching and practical assistance. A relative's anxiety cannot authorise imposed contraception or sterilisation.

Capacity for sexual relations, contraception, medical treatment and particular parenting decisions must be considered separately.

7.6 Abuse and safeguarding: clinical knowledge

Dependence on carers, intimate care, communication barriers, isolation and learned compliance may increase vulnerability and hinder disclosure. Abuse can be physical, sexual, psychological, financial or organisational, and includes neglect, coercion and exploitation.

New fear of someone, regression, disturbed sleep, withdrawal, sexualised behaviour, missing money or unexplained recurrent injury warrant assessment. Trauma may present as altered behaviour without a verbal description of intrusive memories.

Medical and safeguarding explanations can coexist. Bruising may result from falls, seizures, self-injury, clotting/platelet disease, liver disease or medicines. Valproate can cause thrombocytopenia. A medical contributor or reassuring carer account does not automatically resolve concern. Bruise colour cannot reliably date an injury.

Documenting a clinical concern differs from proving what happened. Address immediate needs while safeguarding processes establish the account, keeping the adult's wishes and communication needs central.

7.7 Autism in adults

The developmental pattern

The two domains remain social communication/interaction differences and restricted, repetitive or inflexible patterns, including sensory differences. They begin during development, even when recognised late. Academic success, fluent speech, relationships and employment do not exclude autism.

Adults may describe exhausting social compensation, literal interpretation, difficulty with implied meaning, strong predictability needs and focused interests. These need developmental context; shyness, eye contact or one questionnaire cannot establish autism.

AQ-10: in adults without moderate/severe intellectual disability, a score ≥6, or clinical suspicion despite the score, prompts comprehensive assessment. It is not a diagnostic threshold. Developmental collateral/documents help; no one instrument is compulsory or sufficient.

Routine, OCD or psychosis?

These conditions can coexist. Reduced expression or interaction is not automatically a negative symptom; a new persecutory belief should not be dismissed as an autistic preoccupation.

No medication treats core autism features. Treat coexisting depression, anxiety, ADHD or psychosis with adaptations. Deterioration may also reflect sensory overload, pain, disrupted support, substances or adverse effects.

7.8 Adult ADHD

Adult expression and differential

The developmental pattern still requires significant symptoms before twelve, persistence for at least six months, cross-setting evidence and impairment. Adult presentations often centre on disorganisation, unfinished tasks, procrastination, poor time management, interrupting, impulsive decisions and internal restlessness.

Bipolar disorder is episodic: mood/energy change and reduced need for sleep distinguish it from persistent developmental ADHD. Depression, worry, sleep deprivation, substances/withdrawal, personality difficulties, thyroid disease and sleep disorders also enter the differential. Dual diagnoses are possible.

DIVA-5 is a DSM-5-based structured interview, not a compulsory NICE test or an ICD-11 diagnostic algorithm. Apply ICD-11 requirements separately. Neither screening scores, stimulant response nor a relative's diagnosis independently confirms ADHD.

Treatment and monitoring

Environmental adjustments and, where indicated, structured ADHD-focused psychological treatment accompany medication.

Retain appetite/weight loss, insomnia, raised pulse/BP, anxiety/agitation, diversion and psychiatric destabilisation for stimulants. Atomoxetine can raise pulse/BP and rarely cause liver injury. Stop ADHD medication during an acute manic/psychotic episode; reconsider it after resolution according to individual benefit and risk.

Adult monitoring: weight six-monthly; pulse/BP before and after dose changes and six-monthly; continuing benefit reviewed at least annually. Missed medication may reveal returning symptoms. Stimulant cessation differs from guanfacine's rebound hypertension risk; planned discontinuation is individualised.

Stimulants and sport

Methylphenidate and amfetamine-type stimulants are restricted during competition. A prescription is not anti-doping permission. A therapeutic use exemption (TUE) may be needed according to competition level and the relevant organisation. Check the actual drug against the applicable year's list.

Stopping just before competition is unreliable: clearance/testing windows vary and symptoms may return. TUE evidence rests on diagnosis, treatment history and clinical need. Alternatives require both clinical suitability and an anti-doping check.

7.9 Capacity and communication are different concepts

Limited speech can coexist with good understanding; fluent speech can conceal difficulty weighing consequences. IQ and conversational fluency cannot replace assessment of the actual decision.

Accessible information, pictures, simpler language, time and a familiar supporter can remove barriers. Repeating words may show recall without understanding; an unconventional response may still communicate a valid choice.

The England/Wales abilities are understand, retain, use or weigh relevant information, and communicate the decision. An unwise choice is not automatically incapacity. Diagnosis does not authorise a relative to consent for an adult.