A liver biopsy of a four-year-old boy indicated that the fructose-1,6-bisphosphatase enzyme activity was 20% of normal. the patient's blood glucose levels were normal at the beginning of a fast but then decreased suddenly. pyruvate and alanine concentrations were also elevated. explain the reason for this symptom.

Fructose-1,6-bisphosphatase is a key enzyme in glycolysis and gluconeogenesis; but in this case, the function of this enzyme in gluconeogenesis is more significant. Gluconeogenesis is reversal of glycolysis by bypassing irreversible reactions of glycolysis and making use of reversible reactions of glycolysis. In turn, compounds such as pyruvate, alanine, and glycerol will eventually be converted back to glucose. In the liver, this glucose can be released in the bloodstream in response to hypoglycemic states (i. e. fasting states).

In the deficiency of fructose-1,6-bisphosphatase, gluconeogenesis will be impaired. Therefore there will be an abnormal decrease in blood glucose levels during fasting. Substrates for gluconeogenesis (i. e. pyruvate and alanine) will then accumulate in the body causing its levels to increase.