WORLD'S RAREST CONDITIONS

Some of the strangest conditions that can affect humans are also among the rarest in the world. How do doctors diagnose and treat these afflictions?

- SCOTT DUTFIELD

There are more than 10,000 rare diseases or conditions that can affect humans.

However, different countries have slightly different definitions of what constitutes a rare disease. For example, the National Organization for Rare Disorders categorises a rare disease as one that affects fewer than 200,000 people in the US, whereas the European Commission classifies a rare disease as one affecting less than five in 10,000 people in the community.

The causes of the world's rarest diseases vary, but according to the National Health Service (NHS) in the UK, around 80 per cent of them are believed to have a genetic origin. More often than not, there's little information about these diseases and how to treat them due to their scarcity. Organisations such as Rare Diseases International are working to expand our knowledge of them and help over 300 million people worldwide living with a rare disease.

ALLERGIC TO WATER

One of the rarest conditions out there is called aquagenic urticaria, often referred to as an allergy to water. As animals made up of around 60 per cent water and who need this liquid to survive, an allergy to water seems inconceivable. Nevertheless, there have been fewer than 100 recorded cases worldwide. Like many other allergic reactions, sufferers of the condition experience rashes and welts on the skin upon direct contact with water. Bathing, rain, sweating and even crying can produce enough water to trigger a reaction. According to the National Organization for Rare Disorders, unlike other urticarias, such as hives, aquagenic urticaria rarely leads to a life-threatening allergic reaction called anaphylaxis. While there is no known cure for the condition, antihistamine medications, topical creams and even ultraviolet light treatments can help manage the symptoms.

GETTING THE ITCH

How water can make a person's skin erupt in itchy lumps

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