A child  rapidly develops hypoglycemia after moderate activity. On physical examination, kidney and liver are found to be enlarged. Histopathology of liver shows deposits of glycogen in an excess amount. Blood examination reveals raised ketone bodies, lactic acid and triglycerides. Which enzyme is deficient in this patient?
Type Ia GSD-Von Gierke’s Disease:

Most common Glycogen Storage Disorder (GSD) in childhood.
Autosomal recessive.
Glucose 6-phosphatase is deficient.

The biochemical hallmarks are:

Hypoglycemia
Lactic acidosis
Hyperlipidemia
Hyperuricemia

Clinical Presentation:
Most commonly present at 3–4 months of age with:

Doll like facies with fat cheeks
Relatively thin extremities
Short stature, protuberant abdomen
Massive hepatomegaly
Kidneys are also enlarged
No splenomegaly
Plasma may be milky due to associated hypertriglyceridemia.

Key Concept: 
Glucose 6-phosphatase is deficient in Von Gierke's disease. It is the most common glycogen storage disorder in childhood.
Reference- Harper’s illustrated biochemistry. 30th edition page no: 179
Glycogen synthase
Endoplasmic reticulum glucose-6-phosphate transporter
Glucose-6-phosphatase
Liver phosphorylase kinase