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
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.