Essential Fructosuria Flashcards
A 25-year-old man is evaluated during a routine health checkup. He has no significant past medical history and is asymptomatic. A random urinalysis reveals the presence of reducing substances, but glucose testing is negative. Further evaluation shows fructose in the urine and serum. Genetic testing confirms a mutation on chromosome 2p. Which of the following is the most likely enzymatic deficiency in this patient?
A) Aldolase B
B) Fructokinase
C) Hexokinase
D) Glucose-6-phosphatase
E) Galactokinase
Answer: Fructokinase
Explanation: Essential Fructosuria is an autosomal recessive condition caused by a deficiency of fructokinase, which converts fructose to fructose-1-phosphate in the liver. In the absence of fructokinase, fructose is metabolized by an alternative pathway via hexokinase, converting fructose to fructose-6-phosphate. Unphosphorylated fructose is not trapped in cells and is excreted in the urine, leading to the presence of reducing substances in the absence of glucose. The condition is asymptomatic and requires no treatment.
Incorrect Answers:
A) Aldolase B deficiency causes hereditary fructose intolerance, which is characterized by symptoms such as vomiting, hypoglycemia, and hepatomegaly upon fructose ingestion.
C) Hexokinase metabolizes fructose as an alternative pathway in Essential Fructosuria but is not deficient.
D) Glucose-6-phosphatase deficiency is seen in Von Gierke disease, leading to severe fasting hypoglycemia.
E) Galactokinase deficiency results in galactosemia, associated with cataracts and reducing substances in urine, but not fructose.
What is the prevalence of Essential Fructosuria?
Up to 1:120,000 live births
What is the genetic location associated with Essential Fructosuria?
Chromosome 2p
What enzyme is deficient in Essential Fructosuria?
Fructokinase
What is the normal function of fructokinase in fructose metabolism?
Converts fructose to fructose-1-phosphate in the liver
How is fructose metabolized in Essential Fructosuria despite fructokinase deficiency?
Fructose is converted to fructose-6-phosphate by hexokinase, and unphosphorylated fructose is excreted in urine
What are the clinical manifestations of Essential Fructosuria?
Asymptomatic
How is Essential Fructosuria diagnosed?
Detection of reducing substances (fructose) in serum and urine
What is the treatment for Essential Fructosuria?
No treatment is required
