The concept of “rare disease” (RD) emerged more clearly in
1978 with the publication of an article (Holzman, 1978) stating that all rare
diseases have common problems: a problem of recognition and a problem
of management as their knowledge is very limited and there is little clinical
research in the field. More recently, the public health dimension of rare
diseases was recognised by the European Commission as well as by
several countries; thus ,specific action plans were developed.
There is no unique definition of when a disease becomes
“rare”. Such a definition depends on the reason for asking the question. There
is a clear answer when considering the prevalence of the disease as a potential
market size for drug development. In this case, rarity is defined as the
threshold under which the cost of developing a drug will not be counterbalanced
by the future profits, due to the small number of affected patients. Different
regions of the world have defined this prevalence threshold as around 1 in 2,000 (precisely 1 in 2,000 in Europe).
For the organisation of health care services, a condition
is considered “rare” when the health professionals have not been trained to
identify it, when they have not heard of it or when the knowledge about such a
condition is not available from commonly used sources of information. The
threshold for this is probably around 1 in 5 000 or 1 in 10 000
From a public health perspective, the rarity starts when
there is no specific code for a disease in International classification
systems, and, as a consequence, when it is not possible to collate data. The
threshold for that is probably around 1 in 1 000.
Therefore, although it is difficult to develop a public
health policy specific for each rare disease, it is possible - and necessary -
to have a global rather than a piecemeal approach in the areas of scientific
and biomedical research, drug research and development, industry policy,
information and training, social benefits, hospitalisation and outpatient care.
Most rare diseases are
life-threatening and chronically debilitating conditions, and the vast majority
of them are genetically determined (van Weely and Leufkens, 2004; Wastfelt et
al, 2004). Among the most common ones there are: Sclerodermia,
Charcot-Marie-Tooth disease, Marfan syndrome, Retinitis Pigmentosa,
Neurofibromatosis, Turner syndrome, Hemophilias, Sickle cell disease, Cystic
fibrosis and Duchenne Muscular Dystrophy. Some other very rare
diseases are known to the general public despite their rarity, such
as Huntington disease and Creutzfeld Jacob disease.
Ensuring equity is not the only reason for considering RD
from a public health perspective. RD are also a true public health issue
through their contribution to morbidity and mortality, although solid data are
very much lacking (See: http://ec.europa.eu/health/ph_threats/non_com/rare_diseases_en.htm).
Depending on the definition, it is estimated that there
are between 5 000 and 8 000 distinct rare diseases,
affecting maybe around 3% of the population in total - in other words, around
13.5 million people in the European Union. Therefore, although the impact of
each rare disease is limited, rare diseases collectively
are a true challenge for public health authorities (Eurordis, 2005).