Progression of the disease

My 5 year-old son has this disease it is getting worse. I would like to learn more about the progression of the disease.

From what I have read and personal experience there is no definitive answer, treatment seems to give better odds for a more normal life, but later in life one may or may not experience more problems such as mineā€¦I know this may not be much help but the information I have seen is very vague.