Parental genomic imprinting

Parental, or genomic, imprinting is a newly described form of genetic regulation, leading to the differential behavior of each parental copy of a gene. The precise mechanism responsible for the imprint, or allele-specific behavior of gene transcription, is still unclear; it is thought that modifications not involving the DNA base sequence (therefore, epigenetic as opposed to genetic) have occurred during the production of egg and sperm that mark genes according to parental origin. Several imprinted genes have been identified that also show allelic differences in cytosine methylation and in the timing of their replication during cell division; the relevance of this finding to imprinting mechanisms awaits further clarification. Despite our incomplete knowledge, the importance of the field of imprinting to the pediatrician is in its contribution to our understanding of the transmission behavior of many human diseases and syndromes, particularly those involving abnormal growth and development. Recent advances in the field will no doubt lead to more widely available diagnostic tools with potential applications as far-reaching as the investigation of unexplained fetal loss, prenatal diagnosis, and disease risk counseling.