The most common congenital malformation anomalies are, according to their incidence, musculoskeletal, cutaneous, and urogenital. The most frequent genitourinary anomalies are renal, testicular, and urethral, respectively. About 10 % of the population has some kind of genital or urinary system anomaly [1].

A rare disease is a disease that occurs infrequently or rarely in the general population. In order to be considered as rare, each specific disease cannot affect more than a limited number of people out of the whole population, defined in Europe as less than one in 2,000 citizens (Orphan Drug Regulation 141/2000).

This figure can also be expressed as 500 rare disease patients out of one million citizens. However, these groups of diseases are rare in occasion, but in crowded areas it means a wide group of population could be affected (EURORDIS, European Organisation for Rare Diseases).

It is important to underline that the number of rare disease patients varies considerably from disease to disease and that most people represented by the statistics in this field suffer from even rarer diseases, affecting only one in 100,000 people or less.

These rare diseases make patients and their families particularly isolated and vulnerable. Despite the rarity of each rare disease, it is always surprising to discover that according to a well-accepted estimation, about 30 million people have a rare disease in the 25 EU countries.

According to the WHO Report on Priority Medicines for Europe and the World, 7 October 2004, “Unfortunately, the epidemiological data that are available are inadequate for most rare diseases to give firm details on the number of patients with a specific rare disease. In general people with a rare disease are not registered in databases. Many rare diseases are summed up as “other endocrine and metabolic disorders” and as a consequence, with few exceptions, it is difficult to register people with a rare disease on a national or international basis, and in a reliable, harmonised way.” In the case of rare cancers, many registries do not publish sufficient data that break down figures of rare tumors by type, even though this information might be available from pathological examination of tissue removed during surgery.

It is worth noting that each and every one of us is, statistically speaking, a carrier of 6–8 genetic abnormalities, which are, usually but not always, recessive ones in their transmission. These abnormalities generally have no consequences, but if two individuals carrying the same genetic abnormality have children, these may be affected.