How common is Angelman Syndrome?

The answer to this question is not precisely known but we do have some estimates. A Swedish study of school age children showed an AS prevalence of about 1/12,000 (Steffenburg, S et al., 1996) and the Danish study of AS children in medical clinics, over an 8 year period when there was 45,000 births, showed a minimum prevalence of 1/10,000 (Petersen, MB et al., 1995). The most recent data comes from an excellent study from Denmark that used multiple, relatively complete ascertainment methods to determine a prevalence of 1/24,000 (Mertz, LG et al., 2013).

Several reports have tried to address the prevalence of AS among groups of individuals with established developmental delay. The results showed rates of 0% (Vercesi, AM et al., 1999), 1999), 1.3% (Aquino, NH et al., 2002), 1.4% (Jacobsen, J et al., 1998), and 4.8% (Buckley, RH et al., 1998). The Buckley paper extrapolated their data in order to compare it to the population of the state of Washington (using 1997 Census Bureau figures) and obtained an estimate of 1/20,000, a number similar to that often quoted, but not referenced in terms of methodology, in a 1992 review paper (Clayton-Smith, J and Pembrey, ME 1992).

There appears to be no reported prevalence studies that have screened newborns to detect rates of AS. Population wide prevalence figures would need to take into consideration that longevity in AS is probably reduced (severe mental delay and seizure presence would be risk factors) but no significant population-based data are available on life span shortening. Likewise, it is not known what percent of individuals with AS are undiagnosed, although this is expected it to be significant. Accordingly, to estimate the number of people with AS living in the society, it would be inaccurate to divide any estimated AS prevalence figure into a total population number.

In summary, AS is seen throughout the world, diagnosed in individuals of all races. Although the true incidence remains unknown due to challenges of early identification, misdiagnosis, etc., it appears that the prevalence of AS among children and young adults is somewhere between 1/12,000 and 1/24,000.

Charles Williams, MD
January 30, 2003
Reviewed 6-25-05
Reviewed 11-4-08
Updated 10-8-2015


Aquino, N. H., E. Bastos, L. C. Fonseca, et al. (2002). “Angelman syndrome methylation screening of 15q11-q13 in institutionalized individuals with severe mental retardation.” Genet Test 6(2): 129-131.

Buckley, R. H., N. DinnoP. Weber (1998). “Angelman syndrome: are the estimates too low?” Am J Med Genet 80(4): 385-390.

Clayton-Smith, J.M. E. Pembrey (1992). “Angelman syndrome.” J Med Genet 29(6): 412-415.

Jacobsen, J., B. H. King, B. L. Leventhal, et al. (1998). “Molecular screening for proximal 15q abnormalities in a mentally retarded population.” J Med Genet 35(7): 534-538.

Mertz, L. G., R. Christensen, I. Vogel, et al. (2013). “Angelman syndrome in Denmark. birth incidence, genetic findings, and age at diagnosis.” Am J Med Genet A 161A(9): 2197-2203.

Petersen, M. B., K. Brondum-Nielsen, L. K. Hansen, et al. (1995). “Clinical, cytogenetic, and molecular diagnosis of Angelman syndrome: estimated prevalence rate in a Danish county.” Am J Med Genet 60(3): 261-262.

Steffenburg, S., C. L. Gillberg, U. Steffenburg, et al. (1996). “Autism in Angelman syndrome: a population-based study.” Pediatr Neurol 14(2): 131-136.

Vercesi, A. M., M. R. Carvalho, M. J. Aguiar, et al. (1999). “Prevalence of Prader-Willi and Angelman syndromes among mentally retarded boys in Brazil.” J Med Genet 36(6): 498.