Gene polymorphism has also been linked to ALI pathogenesis, such as insertion/deletion in the angiotensin-converting enzyme gene [101], and variant alleles of Pre-B-cell colony-enhancing factor (PBEF)[102], interleukin 18 (IL-18) [103], and mannose-binding lectin-2 (MBL-2) [104]. Here, IL18 is linked to acute respiratory distress syndrome.