Findings typically present in affected individuals 
  • Normal prenatal and birth history, normal head circumference at birth, no major birth defects.
  • Normal metabolic, hematologic, and chemical laboratory profiles.
  • Structurally normal brain by magnetic resonance imaging (MRI) or computed tomography, although mild cortical atrophy or dysmyelination may be observed.
  • Delayed attainment of developmental milestones without loss of skills.
  • Evidence of developmental delay by age 6 to 12 months, eventually classified as severe.
  • Speech impairment, with minimal to no use of words; receptive language skills and nonverbal communication skills higher than expressive language skills.
  • Movement or balance disorder, usually ataxia of gait and/or tremulous movement of the limbs.
  • Behavioural uniqueness, including any combination of frequent laughter/smiling; apparent happy demeanour; excitability, often with hand-flapping movements; hypermotoric behavior; short attention span.
Findings in more than 80% of affected individuals
  • Delayed or disproportionately slow growth in head circumference, usually resulting in absolute or relative microcephaly by age 2 years.
  • Seizures, usually starting before age 3 years.
  • Abnormal electroencephalogram (EEG), with a characteristic pattern of large-amplitude slow-spike waves.
Findings in fewer than 80% of affected individuals
  • Flat occiput.
  • Occipital groove.
  • Protruding tongue.
  • Tongue thrusting; suck/swallowing disorders.
  • Feeding problems and/or muscle hypotonia during infancy.
  • Prognathia.
  • Wide mouth, wide-spaced teeth.
  • Frequent drooling.
  • Excessive chewing/mouthing behaviours.
  • Strabismus.
  • Hypopigmented skin, light hair and eye color (compared with family); seen only in those with a deletion.
  • Hyperactive lower-extremity deep-tendon reflexes.
  • Uplifted, flexed arm position especially during ambulation.
  • Wide-based gait with out-going (i.e., pronated or valgus-positioned) ankles.
  • Increased sensitivity to heat.
  • Abnormal sleep-wake cycles and diminished need for sleep.
  • Attraction to/fascination with water; fascination with crinkly items such as certain papers and plastics.
  • Abnormal food-related behaviours.
  • Obesity (in the older child; more common in those who do not have a deletion).
  • Scoliosis.
  • Constipation.

From: “Genetics in Medicine:”Clinical and genetic aspects of Angelman Syndrome.” Charles A Williams, MD, Daniel J Driscoll, PhD, MD and Aditi I. Dagli MD. May 2010 © 2010 Lippincott Williams & Wilkins

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