Objective      To investigate the methylation level of suppressor of cell signaling 3 (SOCS3) promoter in the myocardia of infants with cyanotic congenital heart defects.       Methods      A total of 34 children with cyanotic (n=18) and acyanotic (n=16) congenital cardiac defects were investigated. Samples from the right ventricular myocardia were collected to detect the

methylation level of SOCS3 promoter CpG island with methylation-specific PCR (MSP) and bisulfite sequencing PCR (BSP). Protein levels of DNA methyltransferase 3A (DNMT3A) and 3B (DNMT3B) were examined by Western blotting.       Results      Compared to the acyanotic group

the cyanotic group displayed the hypermethylation of SOCS3 promoter CpG island

higher protein level of DNMT3A (0.407±0.469 vs 0.160±0.034

P

0.05)

and similar protein level of DNMT3B (0.054±0.012 vs 0.052±0.093

P

0.05).        Conclusion      SOCS3 promoter CpG island presents hypermethylation in the infants with cyanotic congenital cardiac defects. Strony expression of DNMT3A  might participate in the hypermethylation of SOCS3 promoter CpG island. The hypermethylated SOCS3 promoter CpG island might not be the major factor regulating SOCS3 transcription in the myocardial adaption to chronic hypoxia. The hypermethylated SOCS3 promoter and higher DNMT 3A expression are possibly the signs of adaptive myocardium to chronic hypoxia.