GENOMIC IMPRINTING AND CANCER

Genomic imprinting is the phenomenon by which individual alleles of ce rtain genes are expressed differentially according to their parent of origin, The alleles appear to be differentially marked during gametoge nesis or during the early part of development. This mark is heritable but reversible from generation to generation, implying a stable epigen etic modification. Approximately 25 imprinted genes have been identifi ed to date, and dysregulation of a number of these has been implicated in tumour development. The normal physiological. role of many imprint ed genes is in the control of cell proliferation and fetal growth, ind icating potential mechanisms of action in tumour formation. Both domin ant and recessive modes of action have been postulated for the role of imprinted genes in neoplasia, as a result of effective gene dosage al terations by epigenetic modification of the normal pattern of allele s pecific transcription. The aim of this review is to assess the importa nce of imprinted genes in,generating tumours and to discuss the implic ations for novel mechanisms of transforming mutation.