Osler's disease, also known as hereditary haemorrhagic telangiectasis (HHT), is a rare hereditary condition in which the patient's capillaries dilate to produce red skin spots and mucous membranes. The symptoms can usually be found on the fingertips, face, lips, mouth, inside the nose and in the digestive tract. The condition can cause serious breathing difficulties, bleeding in the lungs and, potentially, blood clots on the brain.

The reason for the changes in the capillaries is unknown, but it is probably due to the genes controlling the way in which the veins grow.

Nose: the most common symptom, usually beginning in childhood, is a sudden nosebleed. The frequency and severity of nosebleeds increases with age. About 95 per cent of people with Osler's experience nosebleeds.

Skin: bulges on the capillaries in the skin, visible on the face as red spots. Often the first red spots appear a few years after the first nosebleeds. The skin bulges are quite fragile and bleed easily.

Stomach: some 30 per cent of sufferers over 50 years of age will experience bleeding from some part of their digestive system. This can cause anaemia.

Lungs: bulges on the lung vessels appear in 33 per cent of all cases. Shortness of breath, especially when exercising, is also a common feature of the disease. A quarter of all patient's with Osler's disease are likely to cough up blood.

Brain: brain aneurysms occur in 10 per cent of people with the disease. Some of these growths are harmless, but others can cause paralysis for short periods of time, epilepsy or brain damage due to bleeding.