porphyria

A portrait of ‘Mad King George’, by Nathaniel Dance. The king suffered from an illness now thought to be porphyria, a rare genetic abnormality that causes various disorders, including mental disturbances.

Group of rare genetic disorders caused by an enzyme defect. Porphyria affects the digestive tract, causing abdominal distress; the nervous system, causing psychotic disorder, epilepsy, and weakness; the circulatory system, causing high blood pressure; and the skin, causing extreme sensitivity to light. No specific treatments exist.

In porphyria the body accumulates and excretes (rather than utilizes) one or more porphyrins, the pigments that combine with iron to form part of the oxygen-carrying proteins haemoglobin and myoglobin; because of this urine turns reddish brown on standing. It is sometimes known as the ‘royal disease’ because sufferers are believed to have included Mary Queen of Scots, James I, and George III.