Twin 2-year-old boys suffering from a rare genetic disease that caused severe pneumonia, low blood sugar and acidosis received successful liver transplants at Renji Hospital, hospital officials announced on Monday. The donated liver was split into two parts for each of the boys. The operation was the world’s first successful liver transplant in twins afflicted with glycogen storage disease (GSD). GSD is a rare inherited disease caused by defective enzymes responsible for converting glucose into glycogen. The twins had GSD type I, which has an incidence rate of one in 100,000. Because GSD occurs mainly in muscles and the liver, symptoms include stunted growth, low blood sugar, an enlarged liver and swollen belly. Patients also face an increased risk of liver tumors, and transplants are the only cure.