Genomic imprinting disorders in humans: a mini-review

Abstract

Mammals inherit two complete sets of chromosomes, one from the father and one from the mother, and most autosomal genes are expressed from both maternal and paternal alleles. Imprinted genes show expression from only one member of the gene pair (allele) and their expression are determined by the parent during production of the gametes. Imprinted genes represent only a small subset of mammalian genes that are present but not imprinted in other vertebrates. Genomic imprints are erased in both germlines and reset accordingly; thus, reversible depending on the parent of origin and leads to differential expression in the course of development. Genomic imprinting has been studied in humans since the early 1980's and accounts for several human disorders. The first report in humans occurred in Prader-Willi syndrome due to a paternal deletion of chromosome 15 or uniparental disomy 15 (both chromosome 15s from only one parent) and similar genetic disturbances were reported later in Angelman syndrome.

Fig. 1

Ideogram of chromosomes 15, showing genes located in the typical deletion region of Prader-Willi syndrome. The locations of genes in the region, 15q11-q13, and their imprinting status are shown. The gene disorder is based on the UCSC Genome Bioinformatics website (http://genome.ucsc.edu). Approximately 40% of subjects with the typical deletion have the larger type I deletion, and approximately 60% have the smaller type II deletion. Abbreviations: Cen, centromere; Tel, telomere; BP, breakpoint; IC, imprinting center; snoRNA, small nucleolar RNA. (Reproduced from Expert Reviews in Molecular Medicine (2005) Vol. 7, e14.)