Fig. 1

Epigenetic disorders found in congenital diseases. a Genomic imprinting is referred to as mono-allelic expression depending on parental origin. The inactivated allele is methylated in its promoter region (filled circle), whereas the expressing allele is not methylated. In some pediatric diseases, both alleles are methylated, resulting in a complete lack of gene expression. b One of two X-chromosomes are normally inactivated in females. In some rare pediatric diseases, both X-chromosomes are active, resulting in severe mental retardation. c DNA is methylated by specific enzymes, such as DNA methyltransferases (DNMTs). In a disease with immunodeficiency [immunodeficiency, centromere instability (ICF) syndrome], mutant DNMT3B fails to methylate DNA in certain genomic regions. d Genes are suppressed by epigenetic mechanism via certain proteins, such as methyl-CpG (cytosine followed by guanine-rich areas) binding proteins. In one autistic disease, denoted as Rett syndrome, mutant methyl-CpG binding protein 2 (MeCP2) fails to suppress its target genes