What is a rare disease?
In New Zealand there is no official definition of what is rare. That is because we have no government or health system policy or programmes which are specific to this category of disorders. And of course, that is something we are trying hard to change.
However there is widespread use of the phrase around the world, and some definitions in various countries which provide useful guidance. NZORD generally follows the European Union policy which defines a disease or disorder as rare when it affects less than 1 in 2000. This definition is in their Orphan Drug Regulation 141/2000.
Another way of defining rare diseases, is to focus on those that are life-threatening or chronically debilitating diseases which are statistically rare, (with an estimated prevalence of less than five in 10,000 or of similarly low prevalence) and have a high level of complexity. This definition is emerging as a preferred definition among Australian and New Zealand groups working to persuade our governments to establish rare disease policy and action plans.
The total number of rare diseases is estimated to be between 6000 and 8000. So while they are individually rare, collectively they may affect up to 8% of the whole population. This estimate is based on a number of surveys and reports from the US and the EU over recent decades.