What is Huntington's Disease? Huntington's Disease (HD) is an inherited, progressively degenerative brain disorder that results in a loss of both mental faculties and physical control. Symptoms usually appear in an individual between 30 – 50 years of age and progress over a 10 to 25 year period. HD affects the individual's ability to think, speak, and walk. Ultimately the weakened individual succumbs to pneumonia, heart failure, or other complications. Presently there is no treatment or cure.