Spinocerebral degeneration
Spinocerebellar degeneration disorder, or spinocerebral ataxia (SCA), causes the cerebellum to atrophy. This results in unsteady and clumsy motion of the body due to a failure of the fine coordination of muscle movements, along with other symptoms. Generally, a sufferer retains full mental capacity while they progressively lose physical control over their body until their death.
Over time, a person inflicted with SCA will be unable to walk, write, talk, and even eat. One day, they won't be able to breathe.
There is no cure for SCA.