Increased incidence of aberrant DNA methylation within diverse imprinted gene loci outside of IGF2/H19 in Silver-Russell syndrome

Almost half of the patients with Silver-Russell syndrome (SRS) are affected by DNA hypomethylation of the Imprinting Center Region 1 (ICR1) at the IGF2 /H19 locus on 11p15. We searched genome-wide for additional aberrant DNA methylation in such SRS patients that could account for the clinical variability of the disorder. For this purpose, 18 children with SRS (11 with ICR1 hypomethylation) and 9 children small for gestational age (SGA), serving as controls, were recruited. Genomic DNA from whole blood was subjected to microarray analysis with the HumanMethylation27 BeadChip. This array allows investigating 27,500 CpG sites mostly located in the promoter regions of 14,000 genes. Data were validated by the methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) technique for the 11p15 region. SRS patients with ICR1 hypomethylation were significantly more frequently affected by DNA hypo-and hypermethylation of CpG sites from diverse imprinted loci than the SGA controls (p = 0.0048). There was no recurrent specific methylation defect outside of IGF2 /H19. These findings suggest as causative in SRS a defective mechanism necessary for establishment or maintenance of imprinting marks, which affects imprinted loci in general with low specificity and the IGF2/H19 locus with high specificity, implying the existence of some structural peculiarities at the IGF2/H19 locus.