Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or of part of a chromosome, from one parent and no copy from the other.[1] UPD can be the result of heterodisomy, in which a pair of non-identical chromosomes are inherited from one parent (an earlier stage meiosis I error) or isodisomy, in which a single chromosome from one parent is duplicated (a later stage meiosis II error).[2] Uniparental disomy may have clinical relevance for several reasons. For example, either isodisomy or heterodisomy can disrupt parent-specific genomic imprinting, resulting in imprinting disorders. Additionally, isodisomy leads to large blocks of homozygosity, which may lead to the uncovering of recessive genes, a similar phenomenon seen in inbred children of consanguineous partners.[3]
UPD has been found to occur in about 1 in 2,000 births.[4]