Diagnosis of Angelman Syndrome (AS) usually occurs somewhere between 9 months and 6 years, the current average is approx. 18 months. In most cases, tests are carried out due to missed developmental milestones, although early onset of seizures or other medical complications can lead to an earlier diagnosis.

Consistent (100% of cases)

  • Developmental delay, functionally severe
  • Minimal or no use of words; receptive and non-verbal communication skills are higher than verbal ones
  • Movement or balance disorder (ataxia), usually a wide legged stiff 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; short attention span; increased sociability

Frequent (more than 80%)

  • Delayed, disproportionate growth in head circumference
  • Seizures, onset usually <3 years of age
  • Abnormal EEG, characteristic pattern with large amplitude slow-spike waves

Associated (20-80%)

  • Tongue thrusting; suck/swallowing disorders
  • Feeding problems during infancy
  • Wide mouth, wide-spaced teeth
  • Frequent drooling
  • Excessive chewing/mouthing behaviours
  • Increased sensitivity to temperature
  • Sleep disturbance
  • Attraction to/fascination with water

A suspected diagnosis of AS can usually be confirmed with a blood test. These tests look for:

  • Parental DNA pattern.This test, known as a DNA methylation test, screens for some of the known genetic abnormalities that cause AS.
  • Missing chromosomes.A chromosomal microarray (CMA) can show if portions of chromosomes are missing.
  • Gene mutation.If the results from a DNA methylation test are normal, a UBE3A gene sequencing test may be required to look for a maternal mutation.

More information on diagnosing Angelman Syndrome can be found here.