SFTPA2 and newborn respiratory distress syndrome: The SP-B Ile131Thr polymorphism (i.e, the threonine allele) has been also associated with high risk of RDS in the first-born preterm twin [17], or has been shown to influence the association between certain SP-A1/SP-A2 haplotypes and RDS suggesting the existence of a gene-gene interaction mechanism [14, 18, 19].