The important feature of a "patient organisation" is that the people who run the organisation have a personal connection to someone with a rare disease. These organisers are often parents of a child with a rare disease, or rare disease patients themselves.
There are many other types of institutions and organisations that help people with rare diseases, such as government institutes and rare disease research foundations. These bodies employ and are directed by paid professionals, who do not usually have a family tie to someone with a rare disease. These organisations are therefore not called "patient organisations."
Patient organisations come in all sizes and flavours. Many are very small; some are very big. Many are organised around a single rare disease in just one country. Others network the smaller groups. Networks can link patients across language borders, connecting people with a disease in Portugal, Holland, Denmark and other European countries. Or groups form by collecting together patient organisations with related diseases, such as chromosome disorders or neuromuscular diseases. Eurordis is an example of the “umbrella” patient organisation that networks and represents at the European government level hundreds of small single-disease patient organisations, cross-border networks, national alliances and other rare disease organisations, in order to use the power of many thousands of individuals to make the voice of rare disease patients heard by the European legislators, and to share among the community the wealth of experience that each smaller organisation brings.