Editing Huntington's disease (section)

==Epidemiology==

The late onset of Huntington's disease means it does not usually affect reproduction.<ref name="lancet07" /> The worldwide [[prevalence]] of HD is 5–10 cases per 100,000 persons,<ref name="emedicine">{{cite web |url=http://emedicine.medscape.com/article/289706-overview |title=Huntington Disease Dementia | vauthors = Sharon I, Sharon R, Wilkens JP, Ersan T |year=2010 |work=emedicine, WebMD |publisher=Medscape |access-date=16 May 2010 |url-status=live |archive-url=https://web.archive.org/web/20100305050654/http://emedicine.medscape.com/article/289706-overview |archive-date=5 March 2010}}</ref><ref name="Driver-Dunckley2007">{{cite book |vauthors=Driver-Dunckley E, Caviness JN |chapter=Huntington's disease| veditors = Schapira AH | title=Neurology and Clinical Neuroscience| publisher=Mosby Elsevier|year=2007| isbn=978-0-323-03354-1|pages=879–885}}</ref> but varies greatly geographically as a result of ethnicity, local migration and past immigration patterns.<ref name="lancet07" /> Prevalence is similar for men and women. The rate of occurrence is highest in [[Ethnic group|peoples]] of Western European descent, averaging around seven per 100,000 people, and is lower in the rest of the world; e.g., one per million people of Asian and African descent. A 2013 epidemiological study of the prevalence of Huntington's disease in the UK between 1990 and 2010 found that the average prevalence for the UK was 12.3 per 100,000.<ref name="lancet07" /><ref name="pmid23482661">{{cite journal | vauthors = Evans SJ, Douglas I, Rawlins MD, Wexler NS, Tabrizi SJ, Smeeth L | title = Prevalence of adult Huntington's disease in the UK based on diagnoses recorded in general practice records | journal = Journal of Neurology, Neurosurgery, and Psychiatry | volume = 84 | issue = 10 | pages = 1156–60 | date = October 2013 | pmid = 23482661 | pmc = 3786631 | doi = 10.1136/jnnp-2012-304636}}</ref> Additionally, some localized areas have a much higher prevalence than their regional average.<ref name="lancet07" /> One of the highest incidences is in the isolated populations of the [[Lake Maracaibo]] region of [[Venezuela]], where HD affects up to 700 per 100,000 persons.<ref name="lancet07" /><ref>{{cite journal | vauthors = Avila-Giróo R |title=Medical and Social Aspects of Huntington's chorea in the state of Zulia, Venezuela |journal=Advances in Neurology |volume=1 |pages=261–6 |year=1973 |issn=0091-3952 |id=NAID 10021247802}}</ref> Other areas of high localization have been found in [[Tasmania]] and specific regions of [[Scotland]], [[Wales]] and [[Sweden]].<ref name="OxfordMonographepi"/> Increased prevalence in some cases occurs due to a local [[founder effect]], a historical migration of carriers into an area of [[geographic isolation]].<ref name="OxfordMonographepi"/><ref name="dnamark">{{cite journal | vauthors = Gusella JF, Wexler NS, Conneally PM, Naylor SL, Anderson MA, Tanzi RE, Watkins PC, Ottina K, Wallace MR, Sakaguchi AY | title = A polymorphic DNA marker genetically linked to Huntington's disease | journal = Nature | volume = 306 | issue = 5940 | pages = 234–8 | year = 1983 | pmid = 6316146 | doi = 10.1038/306234a0 | bibcode = 1983Natur.306..234G | s2cid = 4320711}}</ref> Some of these carriers have been traced back hundreds of years using [[genealogy|genealogical]] studies.<ref name="OxfordMonographepi"/> Genetic [[haplotype]]s can also give clues for the geographic variations of prevalence.<ref name="OxfordMonographepi"/><ref name="pmid7881406">{{cite journal | vauthors = Squitieri F, Andrew SE, Goldberg YP, Kremer B, Spence N, Zeisler J, Nichol K, Theilmann J, Greenberg J, Goto J | title = DNA haplotype analysis of Huntington disease reveals clues to the origins and mechanisms of CAG expansion and reasons for geographic variations of prevalence | journal = Human Molecular Genetics | volume = 3 | issue = 12 | pages = 2103–14 | date = December 1994 | pmid = 7881406 | doi = 10.1093/hmg/3.12.2103}}</ref> [[Iceland]], on the contrary, has a rather low prevalence of 1 per 100,000, despite the fact that [[Icelanders]] as a people are descended from the early Germanic tribes of Scandinavia which also gave rise to the [[Swedes]]; all cases with the exception of one going back nearly two centuries having derived from the offspring of a couple living early in the 19th century.<ref>{{cite journal | vauthors = Sveinsson O, Halldórsson S, Olafsson E | title = An unusually low prevalence of Huntington's disease in Iceland | journal = European Neurology | volume = 68 | issue = 1 | pages = 48–51 | date = July 2012 | pmid = 22722209 | doi = 10.1159/000337680 | s2cid = 207551998}}</ref> [[Finland]], as well, has a low incidence of only 2.2 per 100,000 people.<ref>{{cite journal | vauthors = Sipilä JO, Hietala M, Siitonen A, Päivärinta M, Majamaa K | title = Epidemiology of Huntington's disease in Finland | journal = Parkinsonism & Related Disorders | volume = 21 | issue = 1 | pages = 46–9 | date = January 2015 | pmid = 25466405 | doi = 10.1016/j.parkreldis.2014.10.025}}</ref>

Until the discovery of a genetic test, statistics could only include [[clinical diagnosis]] based on physical symptoms and a family history of HD, excluding those who died of other causes before diagnosis. These cases can now be included in statistics; and, as the test becomes more widely available, estimates of the prevalence and incidence of the disorder are likely to increase.<ref name="OxfordMonographepi"/><ref name="pmid11595021">{{cite journal | vauthors = Almqvist EW, Elterman DS, MacLeod PM, Hayden MR | title = High incidence rate and absent family histories in one quarter of patients newly diagnosed with Huntington disease in British Columbia | journal = Clinical Genetics | volume = 60 | issue = 3 | pages = 198–205 | date = September 2001 | pmid = 11595021 | doi = 10.1034/j.1399-0004.2001.600305.x | s2cid = 19786394}}</ref>