In a study on the United States population, it was found that some SP-A alleles/haplotypes were susceptible factors of RDS, such as (1A0, 6A2, 1A0/6A2), and some SP-A alleles/haplotypes were protective factors of RDS, such as (1A5, 6A4, 1A5/6A4) (25); However, the results obtained in the population study in South Korea were the opposite (22). This evidence concerns the gene SFTPA2 and newborn respiratory distress syndrome.