Type II citrullinemia is primarily found in the Japanese population, where it occurs in an estimated one in 100,000 to 230,000 individuals. Type II has also been reported in people from East Asian and Middle Eastern populations. Mutations in the "SLC25A13" gene are responsible for type II citrullinemia. This gene makes a protein called citrin, which normally shuttles certain molecules in and out of mitochondria. These molecules are essential for the urea cycle and are also involved in making proteins and nucleotides. Mutations in "SLC25A13" typically prevent the production of any functional citrin, which inhibits the urea cycle and disrupts the production of proteins and nucleotides. The resulting buildup of ammonia and other toxic substances leads to the symptoms of type II citrullinemia. Researchers have found many infants with neonatal intrahepatic cholestasis have the same mutations in the "SLC25A13" gene as adults with type II citrullinemia.