The role of imprinted genes in humans.

Genomic imprinting, a process of epigenetic modification which allows the gene to be expressed in a parent-of-origin specific manner, has an essential role in normal growth and development. Imprinting is found predominantly in placental mammals, and has potentially evolved as a mechanism to balance parental resource allocation to the offspring. Therefore, genetic and epigenetic disruptions which alter the specific dosage of imprinted genes can lead to various developmental abnormalities often associated with fetal growth and neurological behaviour. Over the past 20 years since the first imprinted gene was discovered, many different mechanisms have been implicated in this special regulatory mode of gene expression. This review includes a brief summary of the current understanding of the key molecular events taking place during imprint establishment and maintenance in early embryos, and their relationship to epigenetic disruptions seen in imprinting disorders. Genetic and epigenetic causes of eight recognised imprinting disorders including Silver-Russell syndrome (SRS) and Beckwith-Wiedemann syndrome (BWS), and also their association with Assisted reproductive technology (ART) will be discussed. Finally, the role of imprinted genes in fetal growth will be explored by investigating their relationship to a common growth disorder, intrauterine growth restriction (IUGR) and also their potential role in regulating normal growth variation.