MTHFR promoter hypermethylation may lead to congenital heart defects in Down syndrome

Altered global methylation levels revealed LINE-1 methylation in young mothers of Down syndrome (DS) compared to controls suggesting the possibility of impaired DNA methylation causing abnormal segregation of chromosome 21. Methylene Tetrahydrofolate Reductase (MTHFR) is one of the major enzymes of the folate metabolism pathway. MTHFR gene polymorphism has been associated with maternal risk for DS. Studies have revealed that increased MTHFR promoter methylation results in the reduction of MTHFR protein activity further leading to increased risk of various diseases. The aim of this study is to compare the levels of MTHFR promoter methylation in all three study groups. A total of 120 subjects were recruited for the study and was divided into the following three groups: Group I (mothers of DS without Congenital Heart Defects (CHD), n = 40); Group II (mothers of DS with CHD, n = 40); and Group III (age matched control mothers, n = 40). Genomic DNA was isolated from 2 ml peripheral blood and bisulfite treatment was done to convert all unmethylated cytosines into uracil followed by PCR amplification for MTHFR promoter region and Sanger's sequencing. Results showed that there was a two fold increase in methylated promoter region of MTHFR gene in group II compared to other groups. None of the methylation pattern was observed in the control group. MTHFR promoter methylation affects folate metabolism which is known to play a role in chromosomal breakage, abnormal chromosomal segregation and genomic instability and therefore a developmental defect in the form of congenital cardiac anomaly.