The study drug, GSK356278, is a possible new medicine for the treatment of Huntington's disease. Huntington's disease, which is often called HD, is caused by a faulty gene that is passed down through families. HD causes damage to nerve cells in the brain which causes them to waste away. As the damage progresses patients develop symptoms that affect every aspect of life. HD reduces people's ability to walk, talk, think, communicate and causes uncontrolled movements. GSK356278 may slow down the progression of damage to nerve cells in people with HD and help with their ability to think.