Complex sentence: It is later discovered that he has a genetic disease that has affect the past three generations of the Rabanisch family that causes a lack of muscle control, degenerating brain function, and death around the age of 44.
Split into simpler sentences: It is later discovered that he has a genetic disease that has affected the past three generations of the Rabanisch family. The condition causes a lack of muscle control, degenerating brain function, and death around the age of 44.