Porphyria

Porphyria is a group of rare disorders, most of them inherited, caused by deficiencies in enzymes along the pathway the body uses to produce heme, the iron-containing component of hemoglobin, leading to a buildup of heme precursors called porphyrins. The acute forms mainly affect the nervous system and can cause severe abdominal pain, vomiting and psychiatric symptoms during attacks, while the cutaneous forms mainly affect the skin, causing blistering and pain on exposure to sunlight. Some historians have suggested that King George III of Britain suffered from an acute porphyria, a theory that remains debated among medical historians.