Effects of the substances on glomerular filtration rate. Patients with glycogen storage disease (GSD) type Ia show renal hyperfiltration early as a sign of beginning nephropathy. We want to explore the effect of 1. an angiotensinogen-converting-enzyme (ACE) and 2. a cyclooxygenase (COX) -inhibitor to show which substance has a greater benefit concerning reduction of the hyperfiltration. By doing this we will achieve a better understanding of the pathomechanism of GSD-nephropathy.