Becker Studies?

Since we are seeing some promise in the exon skipping, I thought I'd ask a question.

Has there ever been a study done on Beckers patients, their specific mutations, and how that affect their muscles over the years?  Everything I've read so far seems to suggest there is fair bit of variety in their abilities over the years, some walking well into their 60s.

I'm obviously getting ahead of myself, but if exon skipping does do what we're all hoping it does (effectively convert Duchenne to Beckers), it would be interesting to know if skipping certain exons generally resulted in greater muscle damage.