[Genomic imprinting].

UNLABELLED

AN EXCEPTION TO THE RULE: For certain genes, alleles are expressed differently depending on whether they originate from the maternal or paternal genome. This is called the parental imprinting. The parental imprinting plays an important role in development and a dysregulation can lead to various disease states. Loss of the parental imprinting or its alteration is implicated in certain genetic diseases and cancers. When the process is altered, two homologous chromosomes may come from the same parent, a situation termed uniparental disomy. GENETIC DISEASE IN MAN: Several genetic diseases in man are known to be related to the parental imprinting. Willi-Prader disease, Angelman disease and Beckwith-Wiedemann disease are the most extensively studied.

MECHANISMS

Some of the underlying mechanisms are known, but several points concerning the parental imprinting remain to be elucidated, particularly the precise nature of the molecular mechanisms and the identification of the genes controlling this genetic process.