Beckwith-Wiedemann syndrome in humans is characterized by \"overgrowth\" in chil

Question

Beckwith-Wiedemann syndrome in humans is characterized by "overgrowth" in childhood, sometimes leading to unusually large parts of the body. An imprinted gene cluster on chromosome 11 is associated with this disease. The cluster contains several genes including Igf2 and H19. Igf2 encodes an insulin-like growth factor that is maternally imprinted, i.e. the maternal copy is not expressed. However, the DNA methylation pattern of this gene is not different between the two homologous chromosomes (maternal and paternal). On the other hand, H19 is also imprinted and its methylation pattern does differ between the two parental chromosomes. H19 is transcribed into a noncoding RNA that appears to silence the transcription of the Igf2 gene in cis (i.e. the gene on the same chromosome). Would you expect the H19 gene to be hypermethylated on the maternally inherited chromosome or the paternally inherited chromosome? Explain your reasoning.

Explanation / Answer

The imprinting center 1 (IC1) of H19 gene is normally hyper methylated on the paternally inherited chromosome only, this is due to genomic imprinting. Genomic imprinting refers to the epigenetic modifications to the DNA in which either the maternal or paternal copy of a specific gene is silenced. Igf2 and H19 are the two genes that are involved in the regulation of growth process. Of these genes, only the paternally inherited H19 gene is methylated.

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