Genomic imprinting and cancer.

Genomic imprinting results in a functional non-equivalence of parental chromosomes, presumably by epigenetic modification of the genome, and is required for normal mammalian development. In general, reciprocal phenotypes are observed in embryos containing alterations in the dosage of parental chromosomes, for example where both copies of chromosomes or chromosomal regions are derived from one parent. These phenotypes indicate that duplications of maternal chromosomes inhibit embryonic growth and proliferation whereas duplications of the paternal genome result in enhanced cell growth and proliferation. Alterations in the dosage of parental chromosomes have recently been observed in some forms of recessive tumour in man. Here we discuss the role and possible mechanisms of genomic imprinting during embryogenesis and attempt to draw parallels between the parental origin of the loss of heterozygosity observed in some human tumours and the developmental phenotypes that arise in mice with similar distortions of parental origin. These observations strongly implicate genomic imprinting in the genesis of some forms of tumour and, more generally, in the genetic predisposition to cancer.