Is there any way to slow down the progression of huntington's chorea ?

Nothing proven: Coenzyme q 10 does help in mice in several studies. The small dose and used early in the disease helped more than the larger in a recent study: (mol cell neuroscience. Feb 2012). If it works in humans is unknown or what dose should be used. Talk to your neurologist, about recommended dose or even enrolling in a study at answer that question.