[ORPHANET] Prevalence of rare diseases: Bibliographic data

Executive summary: 

A systematic survey of the literature is being performed in order to provide an estimate of the prevalence of rare diseases in Europe. An updated report will be published regularly and will replace the previous version. This update contains new epidemiological data and modifications to existing data for which new information has been made available.

Search strategy

The search strategy is carried out using several data sources:

  • Websites: Orphanet, e-medicine, GeneClinics, EMA and OMIM ;
  • Registries, RARECARE
  • Medline is consulted using the search algorithm: «Disease names» AND Epidemiology[MeSH:NoExp] OR Incidence[Title/abstract] OR Prevalence[Title/ abstract] OR Epidemiology[Title/abstract] ;
  • Medical books, grey literature and reports from experts are also important sources of data.

Collected data

Prevalence values provided are the mean of the highest and lowest values collected. When prevalence is not documented we calculate it using incidence:

  • For congenital diseases with birth-onset, prevalence = incidence at birth x (patient life expectancy/ general population life expectancy) ;
  • For the other rare diseases, prevalence = incidence x rare disease mean duration ;

When no prevalence or incidence data are available, the number of cases or families reported in the literature is provided. The * sign indicates a life time prevalence. The ** sign indicates a birth prevalence. It was used when the birth prevalence was the only data available and a prevalence estimate was not possible because of a large variability in the duration of the disease. NB: Life expectancy of the French population (81 years) is used as the general population life expectancy.

Updated Data

New information from available data sources: EMA, new scientific publications, grey literature, expert opinion. Limitation of the study The exact prevalence rate of each rare disease is difficult to assess from the available data sources. There is a low level of consistency between studies, a poor documentation of methods used, confusion between incidence and prevalence, and/or confusion between incidence at birth and life-long incidence. The validity of the published studies is taken for granted and not assessed. It is likely that there is an overestimation for most diseases as the few published prevalence surveys are usually done in regions of higher prevalence and are usually based on hospital data. Therefore, these estimates are an indication of the assumed prevalence but may not be accurate.