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. 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). 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.UPD has been found to occur in about 1 in 2,000 births. Pathophysiology
UPD can occur as a random event during the formation of egg cells or sperm cells or may happen in early fetal development. It can also occur during trisomic rescue. When the child receives two (different) homologous chromosomes (inherited from both grandparents) from one parent, this is called heterodisomic UPD. Heterodisomy (heterozygous) indicates a meiosis I error if the gene loci in question didnt cross over. When the child receives two (identical) replica copies of a single homologue of a chromosome, this is called an isodisomic UPD. Isodisomy (homozygous) indicates either a meiosis II (if the gene loci in question didnt cross over) or postzygotic chromosomal duplication.
The remainder is attributed to secondary causes: vascular problems, infections and various other conditions. History
The importance of severe headaches in the diagnosis of subarachnoid hemorrhage has been known since the 1920s, when London neurologist Charles Symonds described the clinical syndrome. The term "thunderclap headache" was introduced in 1986 in a report by John Day and Neil Raskin, neurologists at the University of California, San Francisco, in a report of a 42-year-old woman who had experienced several sudden headaches and was found to have an aneurysm that had not ruptured. References
Further reading
Dodick, DW (1 January 2002). "Thunderclap headache". Journal of Neurology, Neurosurgery & Psychiatry. 72 (1): 6–11. doi:10.1136/jnnp.72.1.6. PMC 1737692. PMID 11784817. Ju, Yo-El; Schwedt, Todd (29 March 2010). "Abrupt-Onset Severe Headaches". Seminars in Neurology. 30 (2): 192–200. doi:10.1055/s-0030-1249229. PMC 3558726. PMID 20352589. Ducros, A; Bousser, MG (9 January 2013). "Thunderclap headache". BMJ. 346 (jan08 15): e8557. doi:10.1136/bmj.e8557. PMID 23303883. S2CID 2537784. == External links ==