Haem is part of many proteins in the body. Most of it is produced as part of haemoglobin which is found in all red blood cells. Haem is made up of a compound called porphyrin with an iron atom attached. The blood is required to carry oxygen around the body and this is done using haemoglobin, with the iron atom attached to haem used to bind and detach oxygen as it is carried between the lungs and the tissues. Haem is also involved in different processes with the cells too.
Disorders of porphyrin and haem metabolism are often caused by defects in specific enzymes. This causes difficulties producing haem and leads to a build-up or excessive excretion of the chemicals involved in haem production as well as a number of physical symptoms.
The most well-known disorders in this group are the Porphyrias which are caused by an accumulation of porphyrins or the chemicals used to make them. There are the acute porphyrias which mainly affect the nervous system and are characterised by a build-up of chemicals in the liver, and the cutaneous porphyrias, where porphyrins accumulating in the skin causes photosensitivity and associated skin conditions. An additional two types of porphyria have both acute and skin symptoms.