Uniparental Disomy and Imprinting Disorders

Uniparental disomy (UPD), the inheritance of both homologues of a chromosome from only one parent, has been reported for nearly all human chromosomes. Depending on its mode of formation and time of occurrence, UPD can be present in all cells of an organism, or restricted to some cell lines as a mosaic UPD. Though its general frequency is unknown, it becomes clinically relevant when it produces homozygosity for recessive pathogenic variations or is associated with chromosomal imbalances. UPDs are well-known for their connection to imprinting disorders. Beyond its clinical and diagnostic significance, detection of UPD has value for research in the identification of putative disease mechanisms and genomic regions of interest. Furthermore, detection of UPD in a cluster of similar clinical cases can lead to the definition of new genetic syndromes and imprinted loci, thereby elucidating imprinting regulation and epigenetic mechanisms in general. In this review, we focus on UPDs originating from meiotic and early postzygotic nondisjunction events and their relevance to imprinting disorders.