A 1-month-old baby boy is brought to his pediatrician because of lethargy. Physi

Question

A 1-month-old baby boy is brought to his pediatrician because of lethargy.

Physical exam show:

Slow motor response

5% on the height and weight chart

Enlarged liver

Laboratory studies show:

Low serum glucose concentration of 25 mg/dl (normal is 70-90 mg/dl)

Low serum insulin

High serum lactate of 9.6 mM (normal is < 2.0 mM)

Liver biopsy shows an increase in stored glycogen

1. Why is insulin low?

2. Which other hormones may be high or low?

For the following two questions, make sure you can explain all the symptoms with your

answers.

3. Which metabolic pathway or pathways may be blocked?

4. Which enzyme is most likely to be deficient? Why?

Explanation / Answer

Glycogen storage Disease Type I (GSD I)

GSD I is a Genetic disease results from the deficiency of Glucose-6-phosphatase (Glucokinase) enzyme

1. Insulin is low in response chronic low levels of glucose

2. High levels of Glucagon and cortisol

3. The two major metabolic pathways blocked due to the deficiency of Glucokinase are Glycogenesis and Glycogenolysis

In normal condition, after high carbohydrate meal high insulin levels direct liver cells to take glucose from the blood, convert it to glucose-6-phosphate with the help of glucokinase enzyme in glycogenesis. After complete digestion of meal, insulin levels fall, and the enzymes in the liver cells begin to remove glucose molecules from the glycogen in the form of G6P, the process known as Glycogenolysis

In GSD I, due to lack of Glucokinase enzyme both Glycogenesis and Glycogenolysis pathways are blocked

4. Glucose-6-phosphatase (Glucokinase ) is deficient, due to inherited defects

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