A mix of both is good. My son has muscular dystrophy and I know exactly which exons on the X chromosome are deleted. He was diagnosed 3-4 years earlier than most boys because I noticed a mildly awkward gait (mothers intuition). They are working on cures at the genetic level. That would not have been possible 10 years ago. To all those who have ever donated to muscular dystrophy association or any other related charity...THANK YOU and treatment is improving by leaps and bounds!