Rare Diseases in numbers(3 MB) is a bibliographic study of the epidemiology of rare diseases initiated by EURORDIS in partnership with Orphanet. The study aims to evaluate the prevalence of a number of rare diseases in Europe and to document, for each disease, the age of onset, life expectancy and mode of inheritance. Preliminary results are available for 359 rare diseases. Other results will be available soon.

The method used is based on a large selection of rare diseases focussing on the more common ones (according to current literature and those most frequently requested in the Orphanet website). Data was obtained from Orphanet, Geneclinics, OMIM, Medline, Medical books, grey literature and experts' reports. The results should be interpreted very cautiously due to the heterogeneity of the sources.

Please note that:

• there is very little documented information on the epidemiology of rare diseases,
• it is important to estimate the total number of people affected and the prevalence per disease,
• the natural history of rare diseases must be assessed in order to adapt care and monitor improvements,
• the exact prevalence rate is difficult to obtain from the available data sources,
• there is little consistency between studies and poor documentation of the methods used,
• the studies confuse incidence and prevalence and incidence at birth and lifelong incidence.

The mode of inheritance of the 359 diseases presented in the study is:

• 26.5% autosomal dominant inheritance
• 28.1% autosomal recessive inheritance
• 13.4% multigenic/multifactorial
• 10.0% several modes of inheritance
• 8.1% sporadic
• 7.0% X-linked inheritance
• 5.8% unknown aetiology.

A systematic survey of the literature is being performed in order to provide an estimate of the prevalence in Europe of most of the rare diseases. A new report is issued every 3 months.

See The prevalence of rare diseases: A bibliographic study