What is porphyria, also known as 'vampire disease'?

Porphyria, also known as 'vampire disease', is a group of rare disorders that affect the production of heme, which is a part of haemoglobin. Skin blisters caused by exposure to sunlight are one of the possible symptoms of these disorders. A woman from US was recently diagnosed with acute intermittent porphyria that's triggered by sulphur, which is found in garlic.