A 10 month old male patient comes with vomiting, lethargy and severe jaundice when weaning was started with fruit juice. Laboratory diagnosis reveals prolonged clotting time, hypoalbuminemia, elevation of bilirubin and transaminase levels. Which of the following enzyme is defective?
Hereditary fructose intolerance
Autosomal Recessive.
Biochemical defect

Deficiency of fructose – 1,6 – bisphosphate Aldolase (Aldolase B).
The gene for aldolase B is on chromosome 9q22.3.
Deficiency of this enzyme activity causes a rapid accumulation of fructose-1-phosphate and initiates severe toxic symptoms when exposed to fructose.

Clinical manifestations

Patients with HFI are asymptomatic until fructose or sucrose (table sugar) is ingested (usually from fruit, fruit juice or sweetened cereal).
Symptoms may occur early in life, soon after birth if food or formulas containing these sugars are introduced into the diet.
Early clinical manifestations resemble galactosemia and include jaundice, hepatomegaly, vomiting, lethargy, irritability and convulsions, hypoglycemia.
Acute fructose ingestion produces symptomatic hypoglycemia. If the intake of the fructose persists, hypoglycemic episodes recur and liver and kidney failure progress, eventually leading to death.
Chronic ingestion results in failure to thrive.

Laboratory diagnosis

Prolonger clotting time, hypoalbuminemia, elevation of bilirubin and transaminase levels.
Proximal tubular dysfunction.
Definitive diagnosis is made by assay of fructaldolase B activity in the liver.
Gene-based diagnosis for the mutation.

Treatment

Complete exclusion of all sources of fructose.

Harper’s illustrated biochemistry. 30th edition page -205
Aldolase A
Aldolase B
Fructokinase
Sucrase