Promoting Excellence : Huntington's Disease Recommendations to the Field : Clinical Manifestations and Epidemiology

The mean age at onset of HD is around 37 years old, but ranges between two and 85, with some cases falling outside this range. In individual cases, disease onset may be difficult to pinpoint, particularly when behavioral and psychiatric changes are considered. In patients who are closely followed, a zone of onset appears spanning three to five years. The presenting symptoms vary. In a review of the nature of onset in 510 HD patients, Di Maio et al. found that neurological symptoms heralded the disease onset in 59 percent of subjects, while psychiatric symptoms were first noted in 23 percent, and 18 percent had both at onset.[1]

Studies of motor onset in the Lake Maracaibo, Venezuela community in which HD is endemic, showed that patients first develop subtle changes in volitional eye movement and clumsiness before they show frank motor changes due to the disease. Initially, people with HD exhibit involuntary, spasmodic movements of limbs and facial muscles. Over the course of years, they lose normal motor functions and become bed bound.[2] This is indicative of most patients with HD.

Juvenile HD, which has a strikingly different phenotype, begins with akinesia, rigidity and dystonia and is often accompanied by myoclonic muscle tremors and twitches or seizures. The progression of HD occurs independent of any therapeutic intervention. It remains unclear whether or not progression rate relates to the CAG repeat length, thus limiting the prognostic value of genetic testing for disease severity and progression.[3,4,5]

Geographic region Prevalence
Grampian/NE Corner of Scotland (Simpson, 1989) 9.94/100,000
Ireland (Morrison, 1995) 6.4/100,000
New South Wales (McCusker, 2000) 6.3/100,000
Glasgow/West of Scotland (Bolt, 1970) 5.2/100,000
Mauritius, Independent Island Republic in the Western Indian Ocean (Hayden, 1981) 4.6/100,000
Hong Kong (Chang, 1994) 3.7/1,000,000
South Africa (Hayden, 1980) 0.0/1,000,000

The prevalence of HD is estimated to be between three and 10 people/100,000 people of European descent.[6,7] Most patients are identified by the presence of a suggestive neurologic course in a patient with a positive family history. However, in a study of symptomatic patients undergoing confirmatory genetic tests in British Columbia, nearly 25 percent had negative family histories. Although in many cases the family history is obscured by misdiagnosis, obfuscation or competitive mortality, researchers estimate that as many as 8 percent of HD patients with negative family histories may reflect new genetic mutations arising from borderline premutations. Moreover, the study of HD likely suffers from under reporting of patients. Studies of mutational flow suggest that accurate diagnosis is poor with late onset HD. Current epidemiologic data show that there are 25,000 to 30,000 HD patients in the United States. On average, five first-degree relatives are at risk for each affected person.

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