Remarkably low fibroblast acid α-glucosidase activity in three adults with Pompe disease

► Some adults with Pompe disease have very low GAA activity in fibroblasts. ► These patients do not carry the most common mutation c.-32-13 T > G. ► Compared to classic-infantile patients they express higher GAA activity in muscle. ► Higher activity in muscle might explain the slowly progressive disease course. ► Different fibroblast and muscle activities are due to cell-type-specific processing.