Liver-specific glucose-6-phosphatase is not present in human placenta

Area of Science:

• Biochemistry
• Genetics
• Metabolic Disorders

Background:

• Type I glycogen storage disease (GSD Ia) results from deficient glucose-6-phosphatase (G6Pase) activity in liver, kidney, and intestine.
• Previous research suggested human placenta might express G6Pase, potentially enabling heterozygote detection.
• This study investigated placental G6Pase to assess its utility in diagnosing GSD Ia.

Purpose of the Study:

• To evaluate the feasibility of detecting GSD Ia in placental tissue.
• To characterize the enzymatic properties of human placental glucose-6-phosphatase.
• To determine if placental G6Pase activity can serve as a reliable marker for GSD Ia.

Main Methods:

• Enzyme activity assays were performed on placental tissue from a patient at risk for GSD Ia.
• The substrate specificity of placental G6Pase was compared to that of normal liver G6Pase.
• Kinetic properties of the placental enzyme were analyzed.

Main Results:

• Placental glucose-6-phosphatase activity was found to be normal in the at-risk patient.
• The placental enzyme exhibited broader substrate specificity, hydrolyzing glucose-6-phosphate, mannose-6-phosphate, beta-glycerol phosphate, and glucose-1-phosphate.
• These properties differ significantly from the highly specific G6Pase found in normal liver.

Conclusions:

• The enzyme deficient in Type I glycogen storage disease (GSD Ia) cannot be reliably detected in placental tissue.
• Placental glucose-6-phosphatase is biochemically distinct from the liver enzyme.
• Prenatal diagnosis of GSD Ia using placental tissue is not feasible based on G6Pase activity.