Surfactant protein A gene locus and respiratory distress syndrome in Finnish premature twin pairs

Background. Surfactant protein A (SP-A) polymorphisms are associated with susceptibility to respiratory distress syndrome (RDS). According to present hypothesis the association between SP-A polymorphisms and RDS may not be applicable to the entire population of premature infants. Aim. The present study was designed to evaluate the associations between SP-A allelic variants and RDS in a population consisting of 198 premature twin pairs. Method. Genotype analysis of the SP-A1 and SP-A2 genes and twin zygosity definition were carried out. Results. The main SP-A1 allele 6A(2) (P=0.030), genotype 6A(2)/6A(2) (P=0.0042) and haplotype 6A(2)-1Adegrees (P=0.016) were over-represented in healthy premature twin infants compared to RDS twins. The homozygous genotype 6A(2)/6A(2) was over-represented in twin pairs of whom both were healthy compared to twins concordant for RDS (odds ratio 0.18, confidence intervals 0.06-0.6, P=0.0016) and born between 32 and 36 weeks. 6A(2)/6A(2) was also over-represented in healthy twin pairs with birth weight sum higher than the median (OR 0.15, CI 0.04-0.6, P=0.0025). Conclusions. In twins, the association between SP-A polymorphism and RDS is different from that seen in premature singleton infants. The factor associated with SP-A genotype-specific susceptibility to RDS appears to be related to the size of uterus and the length of gestation at birth.