SLC25A13 deficiency, caused by a large number of possible mutations, underlies two recessive Mendelian metabolic diseases: neonatal intrahepatic cholestasis (NICCD) characterized by liver bile salt accumulation and elevated citrulline plasma levels in infants and Type II Citrullinemia (CTLN2), which is characterized by elevated citrulline plasma levels in adults [31]. This evidence concerns the gene SLC25A13 and metabolic disease.