5.15.2. Data sources

As regards the list of RD, two main databases are listing thousands of rare diseases: OMIM and Orphanet, plus a third database called NORD.

OMIM is the Online version of the Mendelian Inheritance in Man. It is a comprehensive knowledge base of human genes and genetic disorders. It consists of full-text overviews of phenotypes which started to be written in the early 1960s on the basis of published articles (McKusick, 2007). OMIM lists 5,760 genetic diseases which are rare. The definition of what is a disease in OMIM is very much linked to the level of knowledge about its genetic origin. When the genes behind phenotypes are not yet identified, the phenotype is the basis for the disease definition. When genes are discovered first, the condition may be split in several genetic diseases.

Orphanet is a database of rare diseases which was established in 1997. It contains a list of over 5 000 RD and provides textual information on 2 100 of them. The RD included in Orphanet are not exclusively genetic diseases as for OMIM, but also infectious RD, rare intoxications, auto-immune diseases, and RD of unknown aetiology (Orphanet, 2005). The definition of what is a disease is based on the phenotypic uniqueness, no matter the number of genes at the origin of the disease.

A third database of RD which is available is maintained by a patients’ umbrella organization: NORD, standing  for National Organization of Rare Disorders (NORD database, 2007). The number of RD for which information is provided is 1,150.

There is no other comprehensive source of information on all RD but hundreds of sources dedicated to a specific RD or a group of RD. Orphanet is tracing them. Currently 5,200 distinct URL addresses are listed. All these resources can be accessed via Orphanet through a query by disease name.

As regard the prevalence of RD in general, and of each RD is particular, there is no comprehensive source of information as most RD have no specific code and, for that reason, cannot be retrieved in most information systems. No survey has ever been designed to assess the prevalence of RD in general. All the figures that are widely used have no identified source. The only source of reliable information may come from the Italian National Register Rare Diseases, which collects data from a few regional registries recently established in Italy.

Orphanet is conducting a permanent analysis of published reports providing information on incidence and prevalence of RD. The published articles only deal with small subsets and their quality is low in general as the studies were mostly conducted by non-epidemiologists. A compilation of the results is published as a report accessible on the Orphanet website. It is updated twice a year. The data is provided by disease. The diseases are listed by alphabetical order and by decreasing prevalence rate.

As regard the natural history of RD, the sources of information are even more limited. Most registries, cohorts and observatories of cases started to be established for research purposes very recently and the data are not publicly available. Orphanet lists 250 registries in Europe which are dedicated to one disease or a group of RD. These registries may be in a position to provide useful information in the future but currently the published data are very limited.

The mortality data is not useful as most RD have no specific ICD code. A pilot survey is ongoing to assess the feasibility to retrieve data from death certificates on the 250 RD which have a specific ICD10 code. The results are not available yet.