Glycogen storage disease type 0 is characterized by a deficiency in the glycogen synthase

Glycogen synthase

Glycogen synthase is an enzyme involved in converting glucose to glycogen. It takes short polymers of glucose and converts them into long polymers....

 enzyme. Although glycogen synthase deficiency does not result in storage of extra glycogen in the liver, it is often classified with the GSDs because it is another defect of glycogen storage and can cause similar problems. Mutations in the liver isoform, GYS2, causes fasting hypoglycemia, high blood ketones, increased free fatty acids and low levels of alanine and lactate. Conversely, feeding in these patients results in hyperglycemia

Hyperglycemia

Hyperglycemia or Hyperglycæmia, or high blood sugar, is a condition in which an excessive amount of glucose circulates in the blood plasma. This is generally a glucose level higher than 13.5mmol/l , but symptoms may not start to become noticeable until even higher values such as 15-20 mmol/l...

and hyperlactatemia.

There are two versions:

• The muscle version involves GYS1.
• The liver version involves GYS2.