About HD

Huntington's disease (HD) is a hereditary neurodegenerative disorder caused by an expansion of the huntington gene on chromosome 4. HD is inherited in an autosomal-dominant fashion so that each child of an affected parent has a 50% chance of developing the disease. Most people with HD develop symptoms in their 40's and 50's. About 10% of patients have an onset of symptoms before age 20 (juvenile HD) and 10% have an onset after 60.

Huntington's disease has three features: a movement disorder, a cognitive disorder, and a psychiatric disorder. Symptoms begin insidiously and progress over many years until death. The average survival time after diagnosis is about 15-20 years. The disease is always fatal and there is no effective cure or treatment to delay the onset.

The HD gene was identified in 1993. It contains a repeating sequence of three base pairs (CAG) called a "triplet repeat." An excess number of these repeats in the gene results in a protein containing an excess number of glutamine units. The normal function of the huntingtin protein is not known. In HD, huntingtin protein encoded by the abnormal gene collects in the nucleus of the cell giving rise to a structure called an inclusion body. The mechanism by which the protein aggregation causes the brain disorder is not fully understood. The neurons may first become dysfunctional, then undergo progressive degeneration and die. Certain neurons appear more vulnerable in HD. Atrophy is most marked in the corpus striatum of the basal ganglia, including the caudate and putamen. In later phases of the disease, other regions of the brain may be affected.

The clinical diagnosis of HD is made on the basis of family history and the presence of one or more of the features of the disease: behavioral/mood problems, cognitive loss, or movement disorder.

Much more information about Huntington's Disease can be found on the National Institutes of Health Web Site.