Angelman syndrome

Page most recently updated 7 September 2026

This page focuses on the reported psychiatric associations, which may be the initial presenting manifestation, and on other clinical features that may assist the psychiatrist or primary care physician in identifying the underlying diagnosis, considered through the lenses of the diagnostic lenses framework.

Angelman syndrome is a rare genetic condition. It usually occurs as a de novo genetic condition, although some inherited forms show autosomal dominant inheritance; therefore, absence of a relevant family history does not exclude the diagnosis. A distinctive presentation may include the combination of severe intellectual disability with absent or minimal speech, a characteristically happy or excitable demeanour with frequent laughter, hand-flapping or other hypermotor behaviours, ataxic gait, and seizures.

It can present with psychiatric features such as autism spectrum disorder (ASD), anxiety, hyperactivity, impulsivity, aggression, stereotypic behaviours, self-injurious behaviour and sleep disturbance. Behavioural manifestations are often distinctive, with frequent smiling and laughter, excitability, hypermotor activity, hand-flapping, oral exploration and a fascination with water. Anxiety and behavioural difficulties can persist into adolescence and adulthood, although hyperactivity, short attention span and sleep disturbance may improve with age. The neurodevelopmental manifestations generally emerge during infancy or early childhood, and late-onset psychiatric presentations in adulthood are not characteristic.

From a morphologic lens perspective, other features include (but are not limited to):

  • Microcephaly

  • Flat occiput

  • Midface retrusion

  • Prognathism

  • Wide mouth

  • Widely spaced teeth

Other characteristic features include severe developmental delay and intellectual disability, with profound impairment of speech and language and markedly impaired communication. Neurological manifestations include ataxia or a broad-based gait, tremulousness of the limbs, hypotonia in early childhood and, in some individuals, later increased tone or movement abnormalities. Seizures are very common and may include multiple seizure types; nonconvulsive status epilepticus can occur and may present with reduced awareness, hypotonia, head drops or subtle myoclonic movements. Sleep disturbance is also very common, with frequent or early awakening, fragmented sleep and irregular sleep-wake cycles. Other features include feeding difficulties, gastroesophageal reflux, constipation, strabismus, scoliosis and obesity, particularly in adulthood. Normal head circumference does not exclude the diagnosis. 

Early diagnosis is important to identify and manage seizures, including potentially subtle nonconvulsive seizures; recognise sleep, feeding, gastrointestinal and musculoskeletal complications; provide appropriate developmental, educational and psychiatric assessment and support; and facilitate genetic counselling and recurrence-risk assessment for the family.

Selected references and further reading — Morphologic lens

Jones KL, Jones MC, del Campo M. Smith's recognizable patterns of human malformation. 8th ed. Philadelphia: Elsevier; 2021.

Reardon W. The bedside dysmorphologist: a guide to identifying and assessing congenital malformations. 2nd ed. Oxford: Oxford University Press; 2016.

Allanson JE, Biesecker LG, Carey JC, Hennekam RCM. Elements of morphology: introduction. Am J Med Genet A. 2009;149A(1):2-5. doi:10.1002/ajmg.a.32601.

Hennekam RCM, Biesecker LG, Allanson JE, Hall JG, Opitz JM, Temple IK, Carey JC; Elements of Morphology Consortium. Elements of morphology: general terms for congenital anomalies. Am J Med Genet A. 2013;161A(11):2726-2733. doi:10.1002/ajmg.a.36249.