5.15.1. Introduction

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

( http://ec.europa.eu/health/ph_threats/non_com/rare_8_en.htm).

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).