Objective: To study the mechanism of marcosomia by investigating insulin-like growth factor 2 (IGF(2))imprinting status, expression level and the promoter usage in the placenta of macrosomia.
Methods: We selected heterozygous cases for Apa I polymorphism in exon 9 of IGF(2) gene and then analyzed its imprinting status in 168 placentas of macrosomia and normal pregnancies. IGF(2) transcription levels and promoter usages in macrosomic and normal placenta were evaluated by using semi-quantitative RT-PCR assay.
Results: Thirty specimens of macrosomic placenta and 30 of normal placenta were identified as heterozygous for IGF(2). All of the heterozygous specimens showed maintenance of imprinting. The expression of placental IGF(2) mRNA (2.2 +/- 1.2) was significantly higher in macrosomia than that of normal weight group (1.6 +/- 0.6, P < 0.05). Of four promoters, P4 was the most powerful, P3 was the second, and P2 was weakest. Transcripts from P1 were the fewest, and they were only detected in two specimens. The value of P4 was 2.06 +/- 1.26, P3 0.99 +/- 0.72, P2 0.20 +/- 0.20 in macrosomia group and P4 2.05 +/- 1.27, P3 0.98 +/- 0.80, P2 0.19 +/- 0.17 in normal group. There were no significant differences between two groups (P > 0.05).
Conclusion: It is possible that over expression of IGF(2) in placenta contributes to macrosomia while the promoter usage and imprinting status are not associated with macrosomia.