Huntington's Disease - Epidemiology

Epidemiology

The late onset of Huntington's disease means it does not usually affect reproduction. The worldwide prevalence of HD 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 seventy per million people, and is lower in the rest of the world, e.g. one per million people of Asian and African descent. Additionally, some localized areas have a much higher prevalence than their regional average. One of the highest prevalences is in the isolated populations of the Lake Maracaibo region of Venezuela, where HD affects up to seven thousand per million people. 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.

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. Indeed, in 2010 evidence emerged from the UK that the prevalence of HD may be as much as twice that previously estimated.