Angelman syndrome is a neurodevelopmental disorder caused by loss of expression or function of the maternally inherited UBE3A allele in the brain. Epilepsy is common, but Angelman syndrome also affects communication, movement, sleep, behaviour and development.
Core clinical features
Angelman syndrome is associated with severe speech impairment, developmental delay or intellectual disability, gait ataxia or tremulous movements and a characteristic behavioural phenotype with frequent smiling, laughter and excitability.
Microcephaly, sleep disturbance and seizures are also common.
How Angelman syndrome occurs
Several different genetic mechanisms can disrupt maternal UBE3A expression, including a maternal 15q11.2-q13 deletion, a pathogenic UBE3A variant, paternal uniparental disomy or an imprinting defect.
The underlying mechanism matters for recurrence-risk counselling and sometimes for phenotype severity.
Epilepsy frequency
GeneReviews reports seizures in up to about 90% of affected individuals.
Epilepsy is more frequent in people with the common 15q11.2-q13 deletion than in some non-deletion molecular subtypes.
Age at seizure onset
Seizures most often begin between 1 and 3 years, although onset can occur at other ages.
Most affected children who develop epilepsy do so by age 5.
Seizure types
Common seizure types include myoclonic, atonic, generalised tonic-clonic and atypical absence seizures.
Multiple seizure types can occur in the same person.
EEG patterns
Angelman syndrome is associated with several characteristic EEG patterns, including high-amplitude slow activity with spike-wave components and posterior rhythmic activity facilitated by eye closure.
These patterns can appear even when clinical seizures are not occurring.
Why EEG abnormalities can lead to overtreatment
Angelman EEG can remain strikingly abnormal after seizures are controlled.
GeneReviews specifically warns against overtreating EEG abnormalities or movement events that are not actually epileptic.
Non-epileptic myoclonus
Adults in particular can develop nonepileptic myoclonus.
These movements may look like seizures but lack an ictal EEG correlate.
Non-convulsive status epilepticus
Non-convulsive status can occur and may present as reduced alertness, head drops, hypotonia, myoclonic activity or loss of previously acquired skills.
Episodes can last for hours or days and require clinical recognition and EEG assessment.
MRI
Brain MRI may be normal or show mild atrophy or dysmyelination.
A structural lesion is not the primary cause of the syndrome.
Treatment
Antiseizure treatment is individualised according to seizure type.
Commonly used medicines include clobazam, levetiracetam, lamotrigine and clonazepam, though comparative evidence is limited.
Rescue medication
People with prolonged seizures or status episodes may require a personalised rescue-medication plan.
Available routes and medicines differ by country.
Development and communication
Communication support is central because speech is severely limited in many people.
Augmentative and alternative communication, occupational therapy, physiotherapy and educational support can be more important to quality of life than seizure frequency alone.
Sleep
Sleep disturbance is very common and can affect both seizure threshold and family wellbeing.
Sleep management is therefore part of neurological care.
Genetic counselling
Recurrence risk varies dramatically by molecular mechanism.
It can be very low in many de novo cases but substantially higher in some imprinting or inherited UBE3A mechanisms, so the exact genetic cause should be established whenever possible.
Worldwide access
Diagnosis requires molecular testing capable of detecting deletion, imprinting, uniparental disomy and sequence variants.
Access to comprehensive testing and specialist communication services remains uneven worldwide.
The central point
Angelman syndrome is not defined by epilepsy alone. Seizures are common, but characteristic EEG abnormalities, nonepileptic movements, communication disability and sleep problems all require careful distinction.
Related reading
Genetics & Epilepsy →
Status Epilepticus & Rescue Medication →
Sources
Medical note: characteristic Angelman EEG abnormalities and nonepileptic movements can be mistaken for seizures; treatment should target confirmed clinical epilepsy.
Evidence checked: September 2026.