[Epigenetic modification of the genetic material. Genomic imprinting and its significance for disease in human beings].

Genomic imprinting is the epigenetic differential marking of maternally and paternally inherited alleles of specific genes or chromosomal subregions during gametogenesis, leading after fertilization to differential expression during development. Expression is thus monoallelic, with one parental allele being expressed, the other silenced. Imprinting implies the existence of a reversible imprinting signal, which is erased in the gonads to be reset according to the sex of the individual. Mutations in imprinted genes are not inherited in a regular Mendelian fashion. The number of identified imprinted genes is now around 35. Three congenital human disorders are known to be caused by errors in the expression pattern of imprinted genes: Prader-Willi syndrome, Angelman syndrome and Beckwith-Wiedemann syndrome. A number of cancers are also caused by errors in imprinted genes.