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Complex Tissue‐Specific Epigenotypes in Russell–Silver Syndrome Associated with 11p15 ICR1 Hypomethylation

Russell–Silver Syndrome (RSS) is a prenatal and postnatal growth retardation syndrome caused mainly by 11p15 ICR1 hypomethylation. Clinical presentation is heterogeneous in RSS patients with 11p15 ICR1 hypomethylation. We previously identified a subset of RSS patients with 11p15 ICR1 and multilocus hypomethylation. Here, we examine the relationships between IGF2 expression, 11p15 ICR1 methylation, and multilocus imprinting defects in various cell types from 39 RSS patients with 11p15 ICR1 hypomethylation in leukocyte DNA. 11p15 ICR1 hypomethylation was more pronounced in leukocytes than in buccal mucosa cells. Skin fibroblast IGF2 expression was correlated with the degree of ICR1 hypomethylation. Different tissue‐specific multilocus methylation defects coexisted in 38% of cases, with some loci hypomethylated and others hypermethylated within the same cell type in some cases. Our new results suggest that tissue‐specific epigenotypes may lead to clinical heterogeneity in RSS.