Knowledge · Prevalence

How common is each condition?

Two columns, two kinds of source. Orphanet gives each rare disease a prevalence class and, where available, a mean estimate; it is the reference for named syndromes. Population studies fill the gaps for the conditions Orphanet does not count (the amelias, polydactyly, syndactyly, brachydactyly) and cross-check the others. Every figure was checked against its original publication in September 2026.

ConditionOrphanetPopulation studies
All limb reduction defectsNot an Orphanet entity4.5 per 10,000 births in Europe, 2003-2012 (EUROCAT)9; Norway 4.4 (1970-2016)9; northern Netherlands 6.9 (1981-2010)3; upper-limb deficiencies 5.6 per 10,000 births in Finland6
Adams-Oliver syndrome1-9 / 1 000 000 prevalence, mean 0.44 per 100,000 (Worldwide); about 398 cases described ORPHA:97411No population figure found
AmeliaNo epidemiological data published ORPHA:1027111.41 per 100,000 births (326 cases in 23.1 million births, 20 registries, 1968-2006)1; Finland: 2.43 per 100,000 births, 0.63 per 100,000 live births (1993-2008)2
Amelia of the upper limbNo epidemiological data published ORPHA:29496711Upper limbs in 54% of single-limb amelia cases1; 26% of amelia cases in Finland2
Amelia of the lower limbNo epidemiological data published ORPHA:29496911Lower limbs in 70% of amelia cases in Finland2
Amniotic band syndrome1-9 / 100 000 birth prevalence, mean 5.3 per 100,000 (Europe) ORPHA:29500011Upper-limb defects from constriction bands: 51 in 753,342 births, about 0.7 per 10,000 (Finland)6
BrachydactylyNo ORPHAcode (umbrella term)Isolated forms are rare, except types A3 and D, which are common5
Cenani-Lenz syndrome<1 / 1 000 000 prevalence (Worldwide); about 30 cases described ORPHA:325811No population figure found
Crossed polysyndactyly<1 / 1 000 000 prevalence (Worldwide); about 12 cases described ORPHA:293511No population figure found
Ectrodactyly (SHFM)1-9 / 100 000 birth prevalence, mean 5.4 per 100,000 (Europe); 1-9 / 100 000 prevalence (Europe) ORPHA:244011Central ray deficiency: 41 in 753,342 births, about 0.5 per 10,000 (Finland), consistent with Orphanet6
Fibular hemimelia1-9 / 100 000 birth prevalence, mean 1.1033 per 100,000 (Worldwide); 1-9 / 100 000 prevalence, mean 1.1033 per 100,000 (Worldwide) ORPHA:9332311All lower-limb deficiencies: 2.8 per 10,000 births (Finland, 266 cases)8
Holt-Oram syndrome1-9 / 1 000 000 birth prevalence, mean 0.7 per 100,000 (Europe) ORPHA:39211No population figure found
Microgastria–limb reduction<1 / 1 000 000 prevalence (Worldwide); about 16 cases described ORPHA:253811No population figure found
PhocomeliaPrevalence unknown ORPHA:287911All forms of phocomelia: 0.74 per 100,000 births (Finland, 7 cases, 1993-2008)2
Poland syndrome1-9 / 100 000 birth prevalence, mean 3.1 per 100,000 (Canada); 1-9 / 100 000 prevalence (Canada) ORPHA:291111No population figure found
PolydactylyNo epidemiological data published ORPHA:2913118.4 per 10,000 births (northern Netherlands, 1981-2010)3; the most common upper-limb anomaly in Korea, where all upper-limb anomalies total 23.5 per 10,000 live births10
Radial aplasia1-9 / 100 000 birth prevalence, mean 2.5 per 100,000 (Worldwide); 1-9 / 100 000 prevalence, mean 2.5 per 100,000 (Worldwide) ORPHA:9332111Radial ray deficiency, all forms: 1.83 per 10,000 births, 13% of them isolated (Finland)7; the isolated share matches Orphanet's figure
Roberts syndromePrevalence unknown; about 150 cases described ORPHA:310311Prevalence unknown; part of the ESCO2 spectrum12
SymbrachydactylyNot an Orphanet entity as such; ORPHA:1570 covers only the rare form affecting hands and feet (2 cases described)Undergrowth category, mainly symbrachydactyly: 91 in 753,342 births, about 1.2 per 10,000 (Finland)6
SyndactylyNo epidemiological data published ORPHA:93458114.7 per 10,000 births (northern Netherlands, 1981-2010; non-syndromic cases fell from 5.2 to 1.1 between 1992 and 2010)3; 5.63 per 10,000 (China, 2007-2019, 13,611 cases)4
Tetra-amelia<1 / 1 000 000 prevalence (Worldwide); about 5 families described ORPHA:330111No population figure found
Thrombocytopenia-absent radius (TAR)1-9 / 1 000 000 birth prevalence, mean 0.5 per 100,000 (Europe) ORPHA:332011No population figure found
Tibial aplasia–ectrodactyly1-9 / 1 000 000 prevalence, mean 0.1 per 100,000 (Europe) ORPHA:332911No population figure found
Tibial hemimelia1-9 / 1 000 000 birth prevalence, mean 0.1 per 100,000 (Europe); 1-9 / 1 000 000 prevalence, mean 0.1 per 100,000 (Europe) ORPHA:9332211All lower-limb deficiencies: 2.8 per 10,000 births (Finland)8
Ulnar hemimelia1-9 / 1 000 000 prevalence (Europe) ORPHA:9332011Ulnar ray deficiency: 33 in 753,342 births, about 0.44 per 10,000, i.e. 4 per 100,000 (Finland)6, above Orphanet's not-yet-validated class

How to read these figures: they describe births, not the number of people living with a condition; ranges are Orphanet's prevalence classes; the named conditions do not add up to the total for limb reduction defects, because most limb differences are isolated deficiencies without a syndrome name. Rates also differ between populations and registries. None of this is medical advice.

Sources

  1. Bermejo-Sánchez E, Cuevas L, Amar E, et al. Amelia: a multi-center descriptive epidemiologic study in a large dataset from the International Clearinghouse for Birth Defects Surveillance and Research, and overview of the literature. Am J Med Genet C Semin Med Genet. 2011;157C(4):288-304. doi.org/10.1002/ajmg.c.30319
  2. Pakkasjärvi N, Syvänen J, Wiro M, Koskimies-Virta E. Amelia and phocomelia in Finland: characteristics and prevalences in a nationwide population-based study. Birth Defects Res. 2022;114(20):1427-1433. doi.org/10.1002/bdr2.2123
  3. Vasluian E, van der Sluis CK, van Essen AJ, et al. Birth prevalence for congenital limb defects in the northern Netherlands: a 30-year population-based study. BMC Musculoskelet Disord. 2013;14:323. doi.org/10.1186/1471-2474-14-323
  4. Chen ZY, Li WY, Xu WL, et al. The changing epidemiology of syndactyly in Chinese newborns: a nationwide surveillance-based study. BMC Pregnancy Childbirth. 2023;23:334. doi.org/10.1186/s12884-023-05660-z
  5. Temtamy SA, Aglan MS. Brachydactyly. Orphanet J Rare Dis. 2008;3:15. doi.org/10.1186/1750-1172-3-15
  6. Koskimies E, Lindfors N, Gissler M, Peltonen J, Nietosvaara Y. Congenital upper limb deficiencies and associated malformations in Finland: a population-based study. J Hand Surg Am. 2011;36(6):1058-1065. doi.org/10.1016/j.jhsa.2011.03.015
  7. Pakkasjärvi N, Koskimies E, Ritvanen A, Nietosvaara Y, Mäkitie O. Characteristics and associated anomalies in radial ray deficiencies in Finland: a population-based study. Am J Med Genet A. 2013;161A(2):261-267. doi.org/10.1002/ajmg.a.35707
  8. Syvänen J, Nietosvaara Y, Ritvanen A, Koskimies E, Kauko T, Helenius I. High risk for major nonlimb anomalies associated with lower-limb deficiency: a population-based study. J Bone Joint Surg Am. 2014;96(22):1898-1904. doi.org/10.2106/JBJS.N.00155
  9. Klungsøyr K, Nordtveit TI, Kaastad TS, et al. Epidemiology of limb reduction defects as registered in the Medical Birth Registry of Norway, 1970-2016: population based study. PLoS One. 2019;14(7):e0219930. Cites the EUROCAT figure for Europe 2003-2012 (Morris et al., 2018). doi.org/10.1371/journal.pone.0219930
  10. Shin YH, Baek GH, Kim YJ, Kim MJ, Kim JK. Epidemiology of congenital upper limb anomalies in Korea: a nationwide population-based study. PLoS One. 2021;16(3):e0248105. doi.org/10.1371/journal.pone.0248105
  11. Orphanet. Orphadata, epidemiological data (product 9), release of 23 June 2026. Licence CC BY 4.0. www.orphadata.com/epidemiology/
  12. Gordillo M, Vega H, Jabs EW. ESCO2 Spectrum Disorder. In: GeneReviews. University of Washington, Seattle. www.ncbi.nlm.nih.gov/books/NBK1153/

These figures say how often each condition occurs. What is known about why it occurs is set out in Causes of dysmelia, and what each condition is in Understanding dysmelia.