6. Databases and epidemiology

Clinical epidemiology, originally confined to the global problems of infectious diseases, became, in the last 50 years, the fundament of today's evidence based medicine. No medical stakeholder is able to oversee the abundance of data describing prevalence, incidence, clinical patterns and health risks from all regions in the world. The majority of studies are concerned with common diseases, but there is still a paucity of data for rare diseases, which came in the scope of medical stakeholders in the last decade.

In RA, as in other rare and very rare disorders, only supranational networks can provide valid data. ENERCA has concentrated on data from the MS of the EU on a

subset of RA. However, it is often overlooked that social-economic conditions and medical practices are different in the different MS, resulting in different recognition of the epidemiological data studied [20]. Frequency is a general term to compare differences between the occurrence of a given disease, in the case of rare anaemias between populations defined by geographic regions or populations of different origin (such as the formerly called races) in a given region. The latter became of paramount importance with the ongoing immigration of people from the Mediterranean basin to North- and Middle Europe and from Asia and Africa to all MS, as mentioned above. The frequency is a useful parameter in any first approach of disease characteristics and a useful tool to decide on the methodology to estimate more precise issues. No one would challenge the fact, that thalassemia is much more frequent in the Mediterranean area or in immigrants within the Northern European countries. However, mathematically defined parameters are needed for research and health care planning. Prevalence, or more exactly prevalence proportion, is the main indicator used for any epidemiological studies in congenital diseases, representing the vast majority of conditions considered in disease category. Paroxysmal Nocturnal Haemoglobinuria (PNH) is an exception, with prevalence being of major significance, alike for the situation of cancers. For very rare anaemias included in ENERCA, usually period prevalence is measured, using a defined number of observation years rather than an index day as used for the so called point prevalence in common diseases. Another useful measure is the number of affected children of all live births in a given observation period; in this case, the period of definition of live birth (e. g. Days after birth) should be indicated, to avoid bias due to early mortality. An effective instrument to measure true prevalence a proportion is obtained with post-natal screening programs, as described for SCD. Ideally, all cases of a given disease or disease category in a population at time should represent the "true" prevalence. However, in the case of rare anaemias, the detection rate (number of detected/number of existing cases) is often less than 1. As shown by the work of ENERCA, there are strong indicators that the detection rates in the MS vary considerably depending on socio-economic conditions, and the same is true for the proportion of misclassifications. These data are of importance for any attempt to harmonize the diagnosis of rare anaemias in the European countries.

An inherent, unsolved problem of all registries is sustainability. Time trends, so important considering the influence of scientific as well as population changes due to both demographic evolution and migration can only be ascertained if sustainability can be guaranteed by resources of much longer duration than available today. Clinical trials, even though primarily directed to progress of therapeutic measures and often dependent on industrial interests are another source of epidemiological data. We hope that final EuorBloodNet standardization will provide solutions to many of these problems.

#### Acknowledgements

We are indebted to the EC projects FP7 Combined Molecular Microscopy for Therapy and Personalized Medication in Rare Anaemias Treatments (CoMMiT-MenT) and H20200 Innovative Training Networks MSCA.ITN.2014 (Relevance) for their financial support. The collaboration of the J. Trujillo and J. Surrallés from the Spanish Network for Rare Diseases Investigation (CIBERER) and of J. Sevilla from the Hospital Infantil Universitario Niño Jesus (Madrid), is acknowledged. We are also grateful for the technical assistance of Mrs. Elena Krishnevskaya in the RBC ektacytometric studies and in the analysis of HHA patients mutations by Next Generation Sequencing (NGS).

The Rare Anaemias DOI: http://dx.doi.org/10.5772/intechopen.86986
