In 1983, a team of researchers, led by Dr. James Gusella from Harvard Medical School, announced they had found a genetic marker linked to Huntington disease on chromosome 4 called 4p16.3, making Huntington disease, or HD, the first genetic disease mapped using DNA polymorphisms.

HD is inherited as an autosomal dominant disease. (In other words, only one of the two copies of the gene need to be mutated to cause disease.) HD causes the death of specific neurons, leading – usually in midlife – to characteristic jerky movements, physical rigidity, and dementia, symptoms that worsen progressively.