Genome-wide analysis of differential DNA methylation in Silver-Russell syndrome

Silver-Russell Syndrome (SRS) is clinically heterogeneous disorder characterized by low birth weight, postnatal growth restriction, and variable dysmorphic features. Current evidence strongly implicates imprinted genes as an important etiology of SRS. Although almost half of the patients showed DNA hypomethylation at the H19/IGF2 imprinted domain, and approximately 7%-10% of SRS patients have maternal uniparental disomy of chromosome 7 (UPD (7) mat); the rest of the SRS patients shows unknown etiology. In this study, we investigate whether there are further DNA methylation defects in SRS patients. We measured DNA methylation in seven SRS patients and five controls at more than 485,000 CpG sites using DNA methylation microarrays. We analyzed methylation changes genome-wide and identified the differentially methylated regions (DMRs) using bisulfite sequencing and digital PCR. Our analysis identifies epimutations at the previously characterized domains of H19/IGF2, providing proof of principle that our methodology can detect the changes in DNA methylation at imprinted loci. In addition, our results showed a novel SRS associated imprinted gene OSBPL5 located on chromosome 11p14 with the probe cg25963939, which is hypomethylated in 4/7 patients (P=0.023, β=-0.243). We also report DMRs in other genes including TGFβ3, HSF1, GAP43, NOTCH4 and MYH14. These DMRs were found to be associated with SRS using GO pathway analysis. In this study, we identified the probe cg25963939, located at the 5'UTR of imprinted gene OSBPL5, as a novel DMR that is associated with SRS. This finding provides new insights into the mechanism of SRS etiology and aid the further stratification of SRS patients by molecular phenotypes.