Some diseases result from mutations in the body, while others are attributed to viruses or other pathogens; others, such as Huntington's Disease, are genetic disorders, meaning they are passed from one generation to the next due to an abnormality in the genetic sequence. Each child of a parent with the disease has a 50% chance of developing this condition, as it is an autosomal dominant disorder; because a parent can pass on either the healthy copy of the impacted gene or the abnormal one, it only takes one parent with the condition to put any children of that parent at risk.
The risk is significant, too - the disease causes a gradual breakdown of the nerve cells in the brain; patients describe the symptoms as having Alzheimer's Disease, Parkinson's Disease, and ALS all at the same time. While these symptoms typically appear between the ages of 30 and 50, if the abnormality of the gene is significant, the onset can be earlier. Symptoms tend to get increasingly worse over a period of 10 to 25 years, including things like personality changes, impaired judgment, involuntary movements, slurred speech, and weight loss, among many, many others. If the disease manifests in a younger person, the onset of symptoms might be different, including, muscle rigidity, seizures, or difficulty paying attention.
When the disease is diagnosed in adulthood, there is a period of between 10 and 30 years before the patient succumbs to pneumonia, heart failure, or complications that emerge as a result of a physical injury, such as a fall. For juveniles, though, the prognosis is only about 10 years. While there is no cure for this disorder, symptoms can be managed, improving not only the person's quality of life, but prolonging life itself.