Huntington's disease

Huntington's disease or Huntington's chorea is an inherited disorder characterized by abnormal body movements called chorea and loss of memory. The incidence is about 1/200,000. The causative gene (which is one of the first identified to cause an inherited disease) is located on chromosome 4. The product of this gene is a protein called huntingtin. The continuous accumulation of huntingtin neuronal cells gives rise to cell death, especially in the frontal lobes and the basal ganglia (mainly in the caudate nucleus) by some unknown mechanism. Huntingtin has a characteristic sequence of 40 or less glutamine residues in the normal form; the mutated huntingtin causing the disease has more than 40 residues.

While theories as to how how the mutation brings about disease remain diverse and speculative, researchers have identified many specific subcellular abnormalities associated with the mutant protein, as well as unusual properties of the protein in vitro. Just as one example, in 2001, Max Perutz discovered that the glutamine residues form a nanotube[?]¹ in vitro, and the mutated forms are long enough in principle to pierce cell membranes.

The symptoms of Huntington's disease usually start in the 4th decade of life and include loss of cognitive functions, personality changes, quick jerking movements of face and body and unsteady gate. The diagnosis is established by neurological examination findings and the demonstration of cell loss, especially in the caudate nucleus, supported by a cranial CT or MRI scan findings. Although dopamine receptor blockers may have restricted benefits, there is no definite treatment for disease.

Unlike most genetic illnesses, the gene which carries Huntington's disease is dominant. This means that a child with one parent with the disease has a 50% chance of contracting the disease. In addition, genetic testing can identify a person who will later contract the disease before any symptoms are present.

Because of these characteristics, Huntingtion's disease touches on many issues of bioethics. Among the ethical dilemmas faced by those who are possible carriers of the disease are whether they should have children, knowing that their children will be of substantial risk of contracting the disease should they carry the disease. Another dilemma, is whether the should be tested for the genetic marker for the disease, knowing that there is no cure for the disease.

Literature :
¹ Proceedings, Volume 99, 5591-5596