Developmental regression — the loss of previously acquired skills — is abnormal and requires prompt assessment, with urgency guided by the speed of loss and associated features. The causes range from treatable metabolic conditions to neurodegenerative disease to abuse and neglect. West syndrome (infantile spasms) is a particularly critical diagnosis: characteristic salaam spasms (brief clusters of head-dropping, arm-extending movements) beginning at 3–12 months are accompanied by hypsarrhythmia on EEG and are associated with severe intellectual disability if not treated within days. Any parent who describes their infant having episodes of head drops or arm jerks must be referred same-day. Duchenne muscular dystrophy is an X-linked condition — calf hypertrophy and Gower's sign (using hands to climb up legs from floor) are the classic examination findings, typically presenting at 3–5 years. Early diagnosis enables genetic counselling and access to specialist treatment. Hand preference before 1 year of age indicates asymmetric motor development and suggests unilateral cerebral pathology until proven otherwise. In speech delay, a child who was saying 10 words at 18 months and has lost them by 22 months is not 'just a bit slow' — this pattern needs prompt assessment. Landau-Kleffner syndrome (acquired epileptic aphasia): children typically develop normally until 3–8 years, then lose language due to continuous epileptiform discharges in the temporal language areas during sleep; the sleep EEG is diagnostic (waking EEG may be normal), and corticosteroids or antiepileptics can restore language if treated early. Language regression in autism typically occurs between 15–24 months after a period of apparently normal development, often with loss of social engagement and the emergence of repetitive behaviours. The RCGP curriculum requires GPs to identify developmental regression as a red flag requiring prompt referral. NICE CG128: language/social regression under 3 years → autism team; language regression over 3 years → paediatrician/paediatric neurologist first; motor regression at any age → paediatrician/paediatric neurologist.

The four developmental domains are semi-independent — a child can have isolated speech delay with normal motor development (hearing loss, ASD, familial language delay), or isolated gross motor delay with normal cognition (cerebral palsy, muscular dystrophy). The domain pattern guides investigation and referral. Corrected age is essential for premature infants: a 6-month-old baby born at 28 weeks gestation has a corrected age of only 3 months and should be assessed against 3-month milestones, not 6-month. Failure to use corrected age leads to massive over-referral of premature infants. Limit ages prompt assessment and referral, but should be interpreted with the child's whole developmental picture and trajectory. Protodeclarative pointing (pointing to share interest — "look at that!") at 12 months is a key ASD screening marker — its absence, combined with no joint attention, is one of the strongest early predictors of autism. This is distinct from protoimperative pointing (pointing to request something) which is preserved in ASD. No single observation should be interpreted alone — NICE advises not to rule out autism because of apparently good eye contact, smiling, affection, pretend play or apparently normal language milestones.

The distinction between expressive-only delay and receptive-expressive delay is the single most important clinical discriminator in speech delay assessment — a child with pure expressive delay who has age-appropriate comprehension (follows two-step commands, understands complex instructions, responds appropriately to questions) has a much more favourable prognosis than a child with impaired comprehension. Pure expressive delay at 18–30 months with good comprehension and good non-verbal communication (pointing, gesturing, eye contact) is often described as 'late talking' — which often improves, but the outcome varies and cannot be predicted reliably. Even 'late talkers' with expressive-only delay benefit from early SALT referral because: (1) the GP cannot reliably distinguish pure expressive delay from early receptive delay or autism in a 10-minute consultation; (2) early SALT input is appropriate regardless of cause; and (3) some late talkers have persistent language difficulties.

Foetal alcohol spectrum disorder (FASD) is a preventable cause of developmental delay in the UK and is consistently underdiagnosed. Key features include: flat philtrum, thin upper lip, small palpebral fissures, short stature, microcephaly, intellectual disability, and executive function difficulties. Any maternal alcohol use during pregnancy warrants FASD consideration. Bilingualism is a critical consideration in speech assessment — bilingual exposure does not cause developmental language disorder. Assess communication in all languages, ideally with an interpreter or bilingual professional where required; a delay across all languages is more concerning than a difference in the dominant language. Adverse childhood experiences (ACEs) — documented in the Felitti et al ACE study — are associated with developmental, cognitive and behavioural difficulties — but social adversity should not be equated with neglect or abuse without assessment. The social history is not separate from the medical history.

Tuberous sclerosis (TSC) is an autosomal dominant neurocutaneous condition — ash-leaf macules are present from birth and may only be visible under a Wood's lamp in fair-skinned children. TSC causes epilepsy (infantile spasms are a common presentation), autism, and intellectual disability. Early diagnosis allows mTOR inhibitor therapy (everolimus) for subependymal giant cell astrocytomas and seizure control. Neurofibromatosis type 1 (NF1) requires a combination of diagnostic criteria or an appropriate molecular diagnosis — GPs should not diagnose NF1 from café-au-lait lesions alone. NF1 is commonly associated with learning difficulties, speech and language problems, and attention difficulties. Consider serum creatine kinase (CK) in boys with global or motor delay, proximal weakness, Gowers' sign or calf hypertrophy (NICE NG127) — Duchenne MD causes markedly raised CK even before clinical weakness is apparent. Early diagnosis enables genetic counselling and specialist treatment. Head circumference must be measured and plotted at every developmental assessment — microcephaly is often subtle and its significance is underappreciated.

Chromosomal microarray has replaced standard karyotype in specialist genetic testing for unexplained GDD — it detects submicroscopic copy number variants that a standard karyotype misses — but the choice of test depends on phenotype and local genetics policy, and is arranged through paediatrics/genetics. Fragile X syndrome is the most common inherited (vs chromosomal) cause of intellectual disability — it is X-linked, so boys are more severely affected, and there is a premutation carrier state in females associated with premature ovarian insufficiency and fragile X-associated tremor/ataxia syndrome (FXTAS). Testing family members of an affected child has significant reproductive counselling implications. Hearing loss is an important treatable contributor to speech and language delay, and glue ear (otitis media with effusion) is common in early childhood — but neurodevelopmental, cognitive, autism and environmental causes should also be considered. Formal audiology is mandatory in all children with speech and language delay and should be the first investigation requested, not the last — requested alongside (not before) SALT referral. The M-CHAT-R/F (Modified Checklist for Autism in Toddlers, Revised with Follow-Up) is a validated toddler screening tool for autism — it is not diagnostic. It is a 20-item parent questionnaire for children aged 16–30 months; the R (revised) version has improved specificity over the original M-CHAT, and the F (follow-up) module provides structured follow-up questions for intermediate-risk scores to reduce false positives. It is freely available and takes about 5 minutes — it may be used locally (for example when there is a language or social concern in this age group) but should not replace developmental history and clinical observation. Scoring: low risk (0–2) = rescreen at next routine check; medium risk (3–7) = complete follow-up interview; high risk (8–20) = refer via the local autism pathway. A positive screen should prompt the follow-up interview and/or referral without waiting for speech therapy assessment results; a negative screen does not exclude autism.

Developmental language disorder (DLD) — previously called specific language impairment (SLI) — is one of the most common neurodevelopmental conditions in children, affecting approximately 7–10% of school-age children. It is defined as a persistent language disorder in a child with normal hearing, normal non-verbal intelligence, no autism, no cerebral palsy and no known genetic syndrome. Children with DLD have significant difficulty with both understanding and using language — grammar, vocabulary, narrative and phonological processing are typically impaired. The prognosis is variable, and difficulties often persist into adolescence; DLD is associated with substantial educational, social and mental health difficulties in adolescence and adulthood. The RCSLT estimates that approximately 1–2 children in every classroom of 30 has DLD. Early identification allows SALT and education support to be put in place. DLD is not a diagnosis of exclusion made in infancy — it requires formal SALT assessment, and the diagnosis is typically established around age 4–5 when non-verbal intelligence can be reliably assessed.

Speech and Language Therapy (SALT) referral should not be delayed pending paediatric assessment — SALT is the most evidence-based intervention for speech and language delay and early intervention is critical. Early, family-centred, needs-led intervention can improve communication, participation, function and family confidence. For autism, NICE CG128 recommends that the ASD diagnostic pathway begins with a multi-agency assessment team — in the UK, referral is typically to a community paediatrics team or Child Development Centre (CDC). The Education, Health and Care Plan (EHCP) — under the Children and Families Act 2014 — replaces the old Statement of Special Educational Needs. A child with significant developmental needs can request an EHCP assessment from the local authority — GP letters supporting the application are important. GPs should be familiar with the EHCP process and able to write supporting letters. Waiting times for ASD assessment are long in many areas — early referral is essential, and GPs should signpost to support organisations (National Autistic Society) while families wait. For speech delay, refer to both audiology and SALT at the same consultation rather than waiting for audiology results before referring to SALT — waiting times for both can be long, so sequential referral doubles the delay to first SALT contact, and even if hearing loss is found SALT input is still needed alongside hearing management. Audiology matters because hearing loss is a common, treatable cause, but it should run in parallel with SALT, developmental and autism referrals, not before them.

The principle of "treatable causes first" is critical in developmental delay — hypothyroidism, hearing loss, PKU, and seizure disorders are all modifiable conditions where delay in treatment causes preventable developmental harm. Congenital hypothyroidism treated within the first 2 weeks of life has an excellent neurodevelopmental prognosis — untreated, it causes cretinism (severe intellectual disability). This is why the newborn bloodspot screen is so important. The Hanen programme ("It Takes Two to Talk") is a parent-training intervention for language delay — evidence shows parental responsiveness to child communication attempts is a key driver of language development, and teaching parents to respond contingently, wait expectantly, and use child-directed speech produces measurable language gains. For autism, NICE CG170 recommends specific social-communication interventions involving play-based strategies with parents, carers and teachers; ABA/EIBI should not be presented as universal or mandatory. Sleep disorders are common in children with ASD and GDD and have a significant impact on the whole family. Melatonin is used only after a structured behavioural sleep plan, with specialist initiation or shared care per the local protocol.

Parent-mediated early intervention for speech delay is a core approach for children under 3 — programmes which train parents to modify their communication behaviours (reducing directives, following the child's lead, expanding utterances, using parallel talk and self-talk) can support language development in pre-schoolers. Children aged 1–3 spend the vast majority of their waking hours with their parents/caregivers, not with SALTs (who see them for limited sessions), so changing the quality of every interaction throughout the day produces far more learning opportunities than clinic-based therapy alone. Specific programmes (e.g. Hanen 'It Takes Two to Talk') may be offered by local services but are not universally required. When families are referred to SALT, the most effective intervention may be offered to the parents rather than directly to the child — explain this proactively to avoid parental disappointment. Screen use is worth discussing because it is modifiable — observational studies (e.g. Chonchaiya 2008, Zimmerman 2007) suggest that background television exposure and heavy screen use in under-2s are associated with reduced parent–child verbal interaction, reduced vocabulary at 24 months and slower language acquisition; the mechanism is displacement of face-to-face serve-and-return interaction. The AAP (American Academy of Pediatrics — international) recommends avoiding screen time under 18 months (excluding video calls with family members), and a maximum of 1 hour per day of high-quality, co-viewed, interactive content for ages 2–5 (not background TV). GPs can ask about screen use when discussing development and suggest positive alternatives without framing parents as the cause of the child's speech delay.

The "30 million word gap" study (Hart and Risley, 1995) demonstrated that children from lower socioeconomic backgrounds hear 30 million fewer words by age 3 than their more advantaged peers — this gap strongly predicts school attainment and life outcomes. Language exposure from birth is a critical developmental intervention, not a parenting nicety. The "serve and return" model of responsive interaction (coined by the Harvard Centre on the Developing Child) is one of the most robust concepts in early child development — infants who experience consistent responses to their vocalisations and gestures develop stronger neural architecture for language, emotional regulation, and executive function. GPs can signpost parents to locally offered parent programmes (such as Hanen), which translate this science into practical parenting techniques. Disability Living Allowance (DLA) for children under 16 is a non-means-tested benefit for children with developmental disability or chronic health conditions — GP support letters significantly increase successful applications. Many families are unaware of their entitlements — proactively asking "Do you know what financial and practical support is available?" is a meaningful clinical intervention. The Bookstart programme (run by BookTrust) is a universal early-years book-gifting programme — families receive a free Bookstart pack around the 9–12 month health visitor review (board books, rhyme cards and reading guidance) and a second pack at age 3. Health visitors and GPs can use the 9–12 month review to: (1) check the Bookstart pack was received; (2) demonstrate how to read interactively with a board book; (3) signpost to library Rhyme Time sessions; and (4) emphasise talking to the baby from birth.

The Annual Health Check for people with learning disabilities is one of the most important primary care quality indicators — it is an NHS England Directed Enhanced Service (DES) and enables systematic health surveillance for a population at high risk of preventable health conditions (hypothyroidism, epilepsy, mental health problems, constipation, obesity). Learning disability is associated with substantially shorter life expectancy — largely due to preventable conditions identified and treated too late. The STOMP programme (Stopping Over-Medication of People with Learning Disability, Autism or Both) was launched in 2016 after data showed that many people with learning disabilities were prescribed antipsychotic medication without a diagnosed mental health condition — often to manage behaviours that challenge. GPs should review all psychotropic prescriptions in patients with learning disabilities at each annual health check, considering deprescribing where appropriate. Transition from paediatric to adult services is consistently identified as the highest-risk period for young people with developmental disabilities — service discontinuity, loss of coordinated care, and social isolation increase rates of mental health crisis, self-harm, and carer breakdown at this time. Active GP monitoring from age 14 with explicit transition planning is a clinical priority. The age 2 developmental review is the most important speech and language screening opportunity in primary care — it is the standardised contact where delayed language development can be identified and early intervention initiated before school entry. In England, the 2-year check is conducted by health visitors using the Ages and Stages Questionnaire (ASQ-3) and the integrated review combining the NHS 2-year check with the Early Years Foundation Stage 2-year progress check from the child's early years setting (nursery/childminder). GPs who see children at the 2-year routine immunisation visit should use this contact proactively to: (1) ask about language development using the 24-month milestones as a guide (50+ words, 2-word combinations); (2) consider the M-CHAT-R/F (a screen, not a diagnostic test) if any language or social concern; (3) check tympanic membranes; and (4) refer to SALT and audiology simultaneously if any delay is identified. The average age of specialist autism diagnosis in the UK is 5–6 years — despite families first raising concerns with GPs at 18–24 months. Reducing this diagnostic delay requires GPs to act on concerns and refer promptly via the local autism pathway.