What is Machado-Joseph Disease?

Machado-Joseph Disease (MJD) occurs because of a fault in a chromosome that results in the production of an abnormal protein. This protein causes nerve cells to die prematurely in a part of the brain called the cerebellum. The damage to the cerebellum initially causes muscular weakness and progresses over time to a total lack of voluntary muscle control and very significant permanent physical disability. This Help Sheet explains some basic information about MJD.