Piedmont and Aosta Valley inter-regional network in the context of the Italian National Network for rare diseases.

In Europe rare diseases (RDs) are defined as "diseases with a prevalence in the European Union (EU) population of less than 5 per 10,000". This definition includes a large group of more than 6,000 diseases,90% of which are genetically determined and which potentially involve all organs (1) . RDs are therefore a very heterogeneous group as far as both clinical and epidemiological aspects are concerned. There are in fact RDs with less severe clinical manifestations and others with important ones which can compromise the quality of life and the life expectancy. Furthermore, some RDs have a prevalence approaching to the 5 per 10,000 limit and therefore affect a significant number of patients. Indeed, from the June 2005 to the December 2013 the Piedmont and Aosta Valley interregional register for RDs collected21,062, with an estimated overall prevalence of RD of45 patients on 10,000 inhabitants. Moreover half of the patients registered are affected by less than 20 diseases or groups of diseases (Table I) that represent the most important burden of care for the regional healthcare systems. On the other hand there are several with a much lower prevalence affecting a very small number of patients (2) . These latter often lack of timely and correct diagnosis and adequate treatment. Moreover, the world-wide orphan drug policies are associated with unacceptably high costs of newly developed drugs and inaccessibility of previously available drugs which become unavailable over time because of limited production by pharmaceutical industries (3). Finally, despite the low prevalence of each disorder, the number of rare disease is fairly high. The European Commission reports that RDs affect a total of 6-8% of the population. Due to all these problems, and to the fact that RDs are often chronic and invalidating or cause early mortality, they represent a significant public health matter of concern in many countries.