Di-Nucleotide Repeat Polymorphisms of the Insulin-Like Growth Factor-1 Gene and Their Association with IGF-1, Insulin-Like Growth Factor-Binding Protein-1 and Birth Size in a Sri-Lankan Cohort

Abstract

Background: Insulin-like growth factor (IGF)-I is implicated in fetal growth. Ethnic variations of IGF-1 have also been suggested. Di-nucleotide repeat polymorphisms of the IGF-1 gene or their association with IGF-1 levels and birth size have not been studied in Sri Lankans. Objectives: To describe IGF-1 di-nucleotide repeat polymorphisms and their association with IGF-1 and IGF-binding protein (IGFBP)-1 levels and birth size in a cohort of Sri Lankans. Methods: A cross-sectional study on 200 mother-newborn pairs was carried out. Maternal and cord blood levels of IGF-1 and IGFBP-1 were measured by enzyme-linked immunosorbent assay. Three di-nucleotide repeat polymorphisms of the IGF-1 gene [cytosine-adenine (CA) repeats in the promoter and 3′ regions and intron 2 cytosine-thymine (CT) repeat] were studied using PCR amplification and fragment analysis. Results:Cord blood IGFBP-1 levels correlated negatively with birth weight (p < 0.01) and crown-heel length (p < 0.05). Wild-type alleles of the CA repeat polymorphisms differed from those reported in other populations. Newborn and maternal intron 2 CT repeat polymorphism showed a significant effect on birth weight (p < 0.01 and p < 0.001, respectively), crown-heel length (p < 0.01) and head circumference (p < 0.01 and p < 0.05, respectively). Promoter region CA repeat polymorphism and intron 2 CT repeat polymorphism in the newborns were significantly (p < 0.05) associated with cord blood IGF-1 levels. Almost all these effects were limited to primiparous pregnancies. Conclusions: In Sri Lankans intron 2 CT repeat polymorphism of the IGF-1 gene appears to be a significant contributor to IGF-1 levels and birth size in primiparous pregnancies.