In clinical practice you will meet patients who have unusual symptoms or combinations of symptoms. Some patients are of an age, sex or ethnicity that is unusual for a particular disease. Others may have a family history where the pattern of people with the condition does not fit with what would be expected.
These could be clues that that the unusual presentation is due to an underlying ‘rare disease’, which often requires special consideration for diagnosis and clinical management.
The definition used by the UK's Department of Health (Nov 2013) is that a rare disease:
Most rare diseases have a genetic basis, and many genetic disorders come into the category of rare diseases. In recognition of the importance to healthcare in recognising and diagnosing rare diseases for the specialist clinical management that may be required, the Department of Health published in November 2013 'The UK Strategy for Rare Diseases’.
There are between 5,000-8,000 different rare diseases (source: Department of Health). Collectively, rare disease is common, affecting 1 in 17 of the population at some point in their life. In other words, it will affect 3 million people currently living in the UK.
Eighty per cent of rare diseases have a known genetic origin. Fifty per cent of new cases are in children; a significant proportion of whom may die young.
The presence of a rare disease does not exclude another commoner condition, but each can complicate the management of the other.
Increasingly, for any given rare disorder, there is availability in the UK for specific: