Glycogen storage disease type 1a (GSD1a) is caused by mutations in the gene of glucose-6
phosphatase (G6PC), encoding the last enzyme of gluconeogenesis and glycogenolysis. To study the
effect of mutations previously identified, but not yet enzymatically characterized, in French GSD1a
patients, we used an in vitro expression system of the human glucose-6 phosphatase (hGlc6Pase)
cDNA. Wild type hGlc6Pase expressed in COS-7 cells exhibited kinetic features comparable to
microsomal Glc6Pase from normal human liver and kidney. Four new mutations inducing aminoacid
changes in the coding sequence, e.g. W77R, A124T, G184E and L211P, were inserted into the
Glc6Pase cDNA by site-directed mutagenesis, and studied after transient expression in COS-7 cells.
All four mutations totally abolished Glc6Pase activity.