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Angelman Syndrome

Fact Sheet

What is Angelman Syndrome?

Angelman Syndrome is a complex genetic disorder that primarily affects the nervous system. Characteristic features of this condition include developmental delay, intellectual disability, severe speech impairment, and problems with movement and balance (ataxia). Most affected children also have recurrent seizures (epilepsy) and a small head size (microcephaly). Delayed development becomes noticeable by the age of 6 to 12 months, and other common signs and symptoms usually appear in early childhood.

Children with Angelman Syndrome typically have a happy, excitable demeanor with frequent smiling, laughter, and hand-flapping movements. Hyperactivity and a short attention span are common. Most affected children also have difficulty sleeping and need less sleep than usual. Some affected individuals have unusually fair skin and light-colored hair.

With age, people with Angelman Syndrome become less excitable, and the sleeping problems tend to improve. However, affected individuals continue to have intellectual disability, severe speech impairment, and seizures throughout their lives. Adults with Angelman Syndrome have distinctive facial features that are described as “coarse.” Some also develop an abnormal side-to-side curvature of the spine (scoliosis). The life expectancy of people with this condition appears to be nearly normal.

How is it manifested?

Consistent (100%)

  • Developmental delay, functionally severe
  • Speech impairment, no or minimal use of words; receptive and non-verbal communication skills higher than verbal ones
  • Movement or balance disorder, usually of gait and/or tremulous movement of limbs
  • Behavioural uniqueness: any combination of frequent laughter/smiling; apparent happy demeanour; easily excitable personality, often with hand flapping movements; hypermotoric behaviour; short attention span

Frequent (more than 80%)

  • Delayed, disproportionate growth in head circumference, usually resulting in microcephaly (absolute or relative) by age 2
  • Seizures, onset usually under 3 years of age
  • Abnormal EEG, characteristic pattern with large amplitude slow-spike waves

Associated (20 – 80%)

  • Hypopigmented skin and eyes
  • Tongue thrusting; suck/swallowing disorders
  • Hyperactive tendon reflexes
  • Feeding problems during infancy
  • Uplifted, flexed arms during walking
  • Prominent mandible
  • Increased sensitivity to heat
  • Wide mouth, wide-spaced teeth
  • Sleep disturbance
  • Frequent drooling, protruding tongue
  • Attraction to/fascination with water
  • Excessive chewing/mouthing behaviors
  • Flat back of head
  • Smooth palms


Diagnosis is made by noting the characteristic cluster of symptoms (listed below). Careful chromosomal study can reveal abnormalities on Chromosome 15 that are consistent with those identified in Angelman Syndrome.

  • A history of delayed motor milestones and then later a delay in general development, especially of speech
  • Unusual movements including fine tremors, jerky limb movements, hand flapping and a wide-based, stiff-legged gait.
  • A happy disposition with frequent laughter
  • A deletion or inactivity on chromosome 15
  • Characteristic facial appearance (but not in all cases)
  • A history of epilepsy and an abnormal tracing


Angelman Syndrome affects an estimated 1 in 12,000 to 25, 000 people. Angelman Syndrome occurs in approximately 1 in 15,000 lives births and affects males and females equally.

Additional Resources:

Canadian Angelman Syndrome Society

Po Box 31092
Edmonton AB T5Z 3P3
Phone: 780-860-8603
Web Site:
The Canadian Angelman Syndrome Society (CASS) is dedicated to educating parents and professionals about Angelman Syndrome by disseminating information and providing support for parents and caregivers of children with Angelman Syndrome

The Angelman Sydrome Foundation of the USA

414 Plaza Drive, Suite 209, Westmont, IL 60559
Phone: 800-IF-ANGEL (800-432-6435), International Calls: 630-734-9267
Web Site:
The Angelman Syndrome Foundation is a national organization of families, caregivers and medical professionals who care about those with Angelman Syndrome. Our mission is to advance the awareness and treatment of Angelman Syndrome through education and information, research, support and advocacy for individuals with Angelman Syndrome, their families, and other concerned parties.

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