Porphyria
Background
The porphyrias are a group of diseases that have a strong hereditary basis that result from a partial failure of the formation of the pigment haem (a component of haemoglobin in the blood and of many proteins and tissue enzymes.) The porphyrias are principally 'over-production diseases' where the build-up of intermediate compounds that cannot be completely converted to haem leads to clinical manifestations. Many of the intermediate compounds or their derivatives, the porphyrins, interact with light and their accumulation leads to various types of light sensitivity of the skin. This is shown by pain, scarring, occasional blistering, altered pigmentation and fragility in the exposed skin. Over-production of some of the other intermediates including the early chemical compounds that form haem lead to the so-called neurovisceral manifestations of the porphyrias. These may or may not be accompanied by excess porphyrin formation and so light sensitivity may or may not occur as well.