The European Union (EU) defines a disease as rare if it affects no more than 5 in 10,000 people in the EU. Up to 8,000 rare diseases exist worldwide. In most cases, rare diseases present a highly complex clinical picture. One thing that they have in common is a typically chronic progression. Sufferers are frequently affected by disabilities and/or have a limited life expectancy. Around 80% of rare diseases have genetic origins or are in part due to genetic damage, and they are seldom curable.