Rett Syndrome
ICD-11 Classification of Rett Syndrome (LD90.0)
In ICD-11-MMS, Rett syndrome is classified under code LD90.0 within developmental anomalies of the nervous system. It denotes a monogenic neurodevelopmental disorder, most often caused by MECP2 variants, marked by early normal development followed by regression of hand skills and language, gait abnormalities and stereotypic hand movements.
When a girl presents with developmental regression after a period of normal early growth, the ICD-11 code clarifies the diagnosis with precision.
In short
Rett syndrome is classified in ICD-11-MMS under code LD90.0, sitting within the chapter on developmental anomalies (block Developmental anomalies of the nervous system). It denotes a distinct neurodevelopmental disorder, predominantly affecting girls and most commonly caused by pathogenic MECP2 variants, characterised by a period of apparently normal early development followed by regression of acquired hand skills and spoken language, gait abnormalities, and the emergence of stereotypic hand movements.The classification, briefly
Under ICD-11, LD90.0 Rett syndrome is coded within the grouping of developmental anomalies of the nervous system rather than as a behavioural or intellectual-disability category — reflecting its recognised monogenic neurodevelopmental basis. This is a shift in emphasis from earlier classifications: ICD-11 treats Rett syndrome as a discrete clinical-genetic entity. Where intellectual or motor sequelae are relevant for the clinical picture, these may be captured with additional ICD-11 codes for associated functioning, in keeping with the linked ICF model of functioning and disability. Confirmation typically rests on the clinical course alongside MECP2 molecular testing.When to refer
Any girl showing developmental regression — loss of acquired purposeful hand use, deceleration of head growth, emergence of midline hand stereotypies, or loss of spoken language after an initial period of typical development — warrants prompt paediatric neurology and genetic evaluation. Early identification supports timely MECP2 testing, family genetic counselling, and a coordinated multidisciplinary therapy plan addressing communication, motor and self-care domains.The Pinnacle way
A clinical AbilityScore® and any diagnosis are formed only at a Pinnacle Blooms Network centre, under qualified clinician care — never from a code or an online form. Once the clinical picture is established, a coordinated plan spans speech and communication therapy, occupational therapy and movement support, with progress tracked using a structured, clinician-administered AbilityScore® assessment.Trusted sources
WHO ICD-11 for Mortality and Morbidity Statistics (LD90.0, Rett syndrome); WHO International Classification of Functioning, Disability and Health (ICF) for capturing associated functioning.Next step — Reviewing a child with developmental regression? [Partner with Pinnacle](/) for coordinated assessment and multidisciplinary therapy.
This is general information, not a diagnosis — a clinical AbilityScore® and any diagnosis are formed only at a Pinnacle Blooms Network centre under qualified clinician care.
What to watch
Regression after typical early development: loss of purposeful hand use, midline hand stereotypies, deceleration of head growth, loss of spoken language, and gait abnormalities in a young girl.
Try this at home
Document the timeline of skill loss precisely — age of regression onset and which skills were lost guides MECP2 testing and differential diagnosis.
Trusted sources
Developed by SETU Consortium · Pinnacle Blooms Network · Last reviewed 2026-06-10 · reviewed every 365 days
This is general information, not a diagnosis. A clinical AbilityScore® and any diagnosis are formed only at a Pinnacle Blooms Network centre, under qualified clinician care.
Frequently asked
What is the ICD-11 code for Rett syndrome?
Rett syndrome is coded LD90.0 in ICD-11-MMS, within the block of developmental anomalies of the nervous system.
Why is Rett syndrome classified as a developmental anomaly rather than an intellectual disability?
ICD-11 recognises Rett syndrome as a discrete monogenic neurodevelopmental entity, most often linked to MECP2 variants. Associated intellectual or motor functioning can be captured with additional ICD-11 codes alongside LD90.0.
How is Rett syndrome confirmed?
Diagnosis rests on the characteristic clinical course of regression after early typical development, supported by MECP2 molecular genetic testing. Assessment must be conducted by qualified clinicians.