In the EU, a rare disease is one which affects fewer than 5
people per 10 000. The number of sufferers may still be high,
however, as there are some 7 000 known rare diseases. Most are
caused by genetic defects, but environmental exposure during
pregnancy or later in life, often in combination with genetic
susceptibility, is another cause. Some are rare forms or rare
complications of common diseases. While signs may be detected at
birth or in childhood, more than 50% of rare diseases appear
during adulthood, and are often life-threatening or chronically
debilitating. Usually there is no effective treatment, but
screening for early diagnosis, followed by suitable care, can
improve quality of life and life expectancy. Rare diseases are a
serious public health concern and a priority in the EU health
and research programmes. EU law and funding for R&D projects aim
to promote the development of orphan drugs for patients with
rare diseases. The EU is promoting optimal prevention, diagnosis
and treatment of rare dis