Chapter 33

Chorea is essentially a disease of the nervous system. The name “chorea” is given to the disease on account of the dancing propensities of those who are affected by it, and it is a very appropriate designation...The hereditary chorea, as I shall call it, is confined to certain and fortunately a few families, and has been transmitted to them, an heirloom from generations away back in the dim past. It is spoken of by those in whose veins the seeds of the disease are known to exist, with a kind of horror, and not at all alluded to except, through dire necessity, when it is mentioned as “that disorder.” It is attended generally by all the symptoms of common chorea, only in an aggravated degree, hardly ever manifesting itself until adult or middle life, and then coming on gradually but surely, increasing by degrees, and often occupying years in its development, until the hapless sufferer is but a quivering wreck of his former self...I have never known a recovery or even an amelioration of symptoms in this form of chorea; when once it begins it clings to the bitter end.—George Huntington, 18721

In 1872, George Huntington provided one of the first descriptions of the disease that was subsequently named after him. His essay was based on his own clinical experience combined with his grandfather's and father's observations of several afflicted families in East Hampton, Long Island.1 As a physician he followed these patients with great interest. He published his famous essay only at age 21; this manuscript remained his sole significant publication.2

It was not until over a century later that the genetic mutation causing HD was localized to chromosome 4p16.3 in 1983.3 The defective gene and the nature of its mutation were identified in 1993 in a unique collaborative effort.4 The discovery of the gene was rendered possible by the analysis of a large HD population in Venezuela. This kindred, thought to be the largest HD population in the world, live in the state of Zulia in the region of Lake Maracaibo, and comprise more than 18,149 individuals spanning 10 generations. Besides the enormous significance in identifying the HD mutation and for genetic research in general, the analysis of the Venezuelan population allowed a detailed description of the clinical picture and natural history of the disease.5,6

In the United States, HD affects approximately 30,000 people (5–10 per 100,000) with another estimated 150,000 at risk for developing the disease. There is a similar and rather uniform prevalence of HD throughout Europe, ranging between 4 and 7 per 100,000 with no clear distribution patterns over the continent. Particularly low rates of HD are encountered in Finland and Japan. Very high frequencies in Latin American countries neighboring Venezuela are probable. Obvious gender disparities among different countries and racial preponderances have not been observed.7

The genetic defect causing HD ...

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