The late onset of<unk>  means it does not usually affect reproduction. The worldwide prevalence of<unk>  is 5–10 cases per 100,000 persons, but varies greatly geographically as a result of ethnicity, local migration and past immigration patterns. Prevalence is similar for men and women. The rate of occurrence is highest in 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<unk>  in the UK between 1990 and 2010 found that the average prevalence for the UK was 12.3 per 100,000. Additionally, some localized areas have a much higher prevalence than their regional average. One of the highest incidences is in the isolated populations of the Lake Maracaibo region of Venezuela, where<unk>  affects up to 700 per 100,000 persons. Other areas of high localization have been found in Tasmania and specific regions of Scotland, Wales and Sweden. Increased prevalence in some cases occurs due to a local founder effect, a historical migration of carriers into an area of geographic isolation. Some of these carriers have been traced back hundreds of years using genealogical studies. Genetic haplotypes can also give clues for the geographic variations of prevalence. Iceland, on the contrary, has a rather low prevalence of 1 per 100,000, despite the fact that Icelanders as a people are descended of 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. Finland, as well, has a low incidence of only 2.2 per 100,000 people. Until the discovery of a genetic test, statistics could only include clinical diagnosis based on physical symptoms and a family history of<unk> , 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.
Huntington's disease
Wilson's disease
Stratton Parker syndrome
Paraneoplastic syndrome
Sandhoff disease
Lupus
X-linked dystonia parkinsonism
Benign hereditary chorea