Genomic imprinting: nature and clinical relevance.

Molecular genetic techniques allow investigators to trace chromosomes and genes from parent to child and, in a single individual, from tissue to tissue. These techniques have uncovered a new type of gene control in which the allele from one parent is expressed and the allele from the other parent is not. This differential expression is called genomic imprinting. It may lead to phenotypic differences when inheritance is from the mother versus the father. Genomic imprinting has been observed in a number of disorders having to do with growth, behavior, and abnormal cell growth. It is important to be aware that such a phenomenon exists and to consider it when making diagnoses and determining therapy.