ICD-11 Classification of Rett Syndrome (LD90.0)

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

Developmental measurement supports care planning; diagnosis requires an appropriately qualified healthcare professional., 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 — individual assessment and diagnosis require an appropriately qualified healthcare professional.