NOS3 and newborn respiratory distress syndrome: However, when the preterm infants were divided into two and three groups based on gestational age and birth weight, a study of the SNP rs1799983 of the NOS3 gene showed that the GG genotype and G allele frequencies were significantly increased in the RDS groups, the GT genotype and A allele were less frequent among the RDS groups in 26–32.9 weeks of gestational age and in a birth weight subgroup of <1.5 Kg.