A form of porphyria inherited as a Mendelian dominant characteristic can cause both cutaneous lesions on the exposed skin and attacks of acute porphyria following certain drugs, for instance barbiturates. Because it presents in a variety of forms it has been named porphyria variegata. This form of porphyria is very common among the White and Coloured South Africans because of 'founder effect'. A high proportion of the present population are descendants of a small number of early settlers, one of whom introduced the gene for this condition. The disease has been traced over 17 generations to Gerrit Jansz who came from Deventer in Holland and who married Ariaantje, an orphan from Rotterdam, in 1688. In the quiescent state porphyria variegata is best diagnosed by the examination of a solution of the stool in ultraviolet light which shows the pink fluorescence of porphyrin. In the acute attack porphobilinogen and porphyrin are greatly increased in the urine. Porphyria variegata also occurs outside of South Africa but in these countries it is less common than acute intermittent porphyria. The diagnosis and treatment is described and the story that the insanity of King George III of England was due to porphyria variegata is refuted.
