Type-1c glycogen storage disease is not caused by mutations in the glucose-6-phosphate transporter gene

Glycogen storage disease type 1 (GSD-1) is a group of autosomal. recessive disorders caused by deficiencies in glucose-6-phosphatase (G6Pase) and the associated substrate/product transporters. Molecular genetic studies have d emonstrated that GSD-1a and GSD-1b are caused by mutations in the G6Pase en zyme and a glucose-6-phosphate transporter (G6PT), respectively. While kine tic studies of G6Pase catalysis predict that the index GSD-1c patient is de ficient in a pyrophosphate/phosphate transporter, the existence of a separa te locus for GSD-1c remains unclear. We have previously shown that the G6Pa se gene of the index GSD-1c patient is intact; we now show that the G6PT ge ne of this patient is normal, strongly suggesting the existence of a distin ct GSD-1c locus.