Huntington's disease is an inherited disease characterized by the progressive loss of brain and muscle function. Symptoms usually begin during middle age. The disease is inherited as an autosomal dominant trait, meaning that a single mutated copy of the responsible gene is sufficient to cause the disease.
Huntington's disease is the classic example of what we call autosomal dominant condition, where an affected individual has one abnormal copy and one normal copy of the gene, and therefore their child has a 50 percent chance of inheriting it. This is a tragic and frustrating condition which comes on in mid-life with a progressive neurological deterioration that extends over more than a decade in many cases, and for which at the present time we don't have adequate therapy, but that is a very high priority for the medical research enterprise. The disease clearly at the present time causes all kinds of havoc in the families that are affected by it. And perhaps the most famous person affected by Huntington's disease was Woody Guthrie.