Genomic imprinting is the phenomenon whereby some genes preferentially produce mRNA transcripts from the gene copy derived from the parent of a specific sex. It has been implicated in a number of human diseases (most of them of endocrine interest), such as Prader-Willi/Angelman syndromes, Silver-Russell syndrome, Beckwith-Wiedemann syndrome, transient neonatal diabetes, the focal form of nesidioblastosis, and pseudohypoparathyroidism.