Disease, Huntington

An hereditary disorder with mental and physical deterioration leading to death. Although characterized as an "adult-onset" disease (as is usually the case), we have seen children with full-blown Huntington disease. Huntington disease describes an autosomal dominant pattern of inheritance with high penetrance (a high proportion of persons with the gene develop the disease). The characteristic findings of Huntington disease are caused by loss of neurons (nerve cells) in the brain. The disease is due a gene in chromosome band 4p16.3. The gene, called HD, contains an unstable repeating sequence of 3 nucleotide bases (CAG) in the DNA. Normal people have an average of 19 CAG repeats and at most 34 such repeats while virtually all patients with Huntington disease have more than 40. The Huntington disease gene codes for a protein that has been named (confusingly) huntingtin whose function is unknown. The elevated numbers of CAG repeats in the Huntington disease gene lead to the production of an elongated huntingtin protein which appears to correlate with the loss of neurons in the disease.