I think in Pompe is the potential for the greatest benefit to patients with ERT+chaperone. Its the ERT (well technically 2) that I am aware of with the poorest uptake into the cells. Unfortunately Amicus's Pompe chaperone has some tox question marks.
In Fabry I think part of the thinking was the incidence may be much higher then thought as many may not be diagnosed till late in life. Reaching these people though may not be easy. I believe it was TKT that also first discovered the incidence in women is much more then was thought (X linked).
Unfortunately, I don't think Fabry is enough to get the company profitable. They announced on their quarterly call a vote to increase the share authorization.