TFF2 and chronic obstructive pulmonary disease: Single nucleotide polymorphisms (SNPs) of the SP genes have been identified and shown to associate with various acute and chronic pulmonary diseases, such as neonatal respiratory distress syndrome (RDS) [15,16,17,18], cystic fibrosis (CF) [19], chronic obstructive pulmonary disease (COPD) [20], and acute respiratory distress syndrome (ARDS) [21].