A rare genetic disease which causes problems from childhood onwards. Most patients have started having problems by the age of four years. Exposure to spring or summer sun causes a burning pain, especially on the banks of the hands, tops of the feet and face, which often last for two to three days, usually with nothing more to see them a bit of mild swelling. Standard painkiller tablets don't usually help but cold air or cold water can relieve the pain a little. Although it is genetic, in many families no one else in the family may have suffered from it previously. Although no treatments are totally effective for the painful attacks, beta carotene and hospital ultraviolet light therapy may help some sufferers. Since the pain is caused by visible light, commercially available sunscreens do not help, but a hospital-prescribed visible light sunscreen can be useful, as can window filter films. Blood tests need checking once a year to check that the very rare liver complications are not occurring.