Uniparental disomy

Uniparental disomy
Classification and external resources
ICD-10 Q99.8
MeSH D024182

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 parent.[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 children of consanguineous partners.[3]


UPD can occur as a random event during the formation of egg or sperm cells or may happen in early fetal development. It can also occur during trisomic rescue.

Animation of uniparental isodisomy


Most occurrences of UPD result in no phenotypical anomalies. However, if the UPD causing event happened during meiosis II, the genotype may include identical copies of the uniparental chromosome (isodisomy), leading to the manifestation of rare recessive disorders. UPD should be suspected in an individual manifesting a recessive disorder where only one parent is a carrier.

Uniparental inheritance of imprinted genes can also result in phenotypical anomalies. Although few imprinted genes have been identified, uniparental inheritance of an imprinted gene can result in the loss of gene function, which can lead to delayed development, mental retardation, or other medical problems.

All chromosomes (uniparental diploidy)

Main article: Molar pregnancy

Occasionally, all chromosomes will be inherited from one parent. A molar pregnancy results from fertilization by two sperm or a duplicated single sperm into an egg with DNA (partial molar pregnancy) or without DNA (complete molar pregnancy). A complete molar pregnancy is diploid (uniparental) and a partial molar pregnancy is triploid. Neither condition ever results in a liveborn infant, and there is an increased risk for choriocarcinoma.


The first clinical case of UPD was reported in 1988 and involved a girl with cystic fibrosis and unusually short stature who carried two copies of maternal chromosome 7.[9] Since 1991, out of the 47 possible disomies, 29 have been identified among individuals ascertained for medical reasons. This includes chromosomes 2, 5–11, 13–16, 21 and 22.

See also


  1. Robinson WP (May 2000). "Mechanisms leading to uniparental disomy and their clinical consequences". BioEssays. 22 (5): 452–9. doi:10.1002/(SICI)1521-1878(200005)22:5<452::AID-BIES7>3.0.CO;2-K. PMID 10797485.
  2. Human Molecular Genetics 3. Garland Science. p. 58. ISBN 0-8153-4183-0.
  3. King DA. "A novel method for detecting uniparental disomy from trio genotypes identifies a significant excess in children with developmental disorders". Genome Research. 24: 673–687. doi:10.1101/gr.160465.113.
  4. 1 2 3 4 "Meiosis: Uniparental Disomy". Retrieved 29 February 2016.
  5. , Angelman Syndrome, Online Mendelian Inheritance in Man
  6. 608149
  7. 32320
  8. Bhatt, Arpan; Liehr, Thomas; Bakshi, Sonal R. (2013). "Phenotypic spectrum in uniparental disomy: Low incidence or lack of study". Indian Journal of Human Genetics. 19 (3): 131–34. doi:10.4103/0971-6866.120819.
  9. Spence JE, Perciaccante RG, Greig GM, Willard HF, Ledbetter DH, Hejtmancik JF, Pollack MS, O'Brien WE, Beaudet AL (1988). "Uniparental disomy as a mechanism for human genetic disease". American Journal of Human Genetics. 42 (2): 217–226. PMC 1715272Freely accessible. PMID 2893543.

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