Fructosuria

Definition of Fructosuria

Excretion of fructose in urine is called as Fructosuria.

Dietary sources

1. Fruit juices and honey

2. Table sugar or sucrose

Biomedical importance

1. Fructose is easily metabolized and is a good source of energy.

2. Seminal fluid is rich in fructose.

3. Excess dietary fructose is harmful and lead to increased synthesis of triglycerides.

Fructose metabolism

Fructose is converted into fructose 1 phosphate in the presence of the enzyme fructokinase and this is further metabolized into D glyceraldehydesand dihydroxyacetone phosphate in the presence of the enzyme aldolase B.

In fructosuric persons aldolase B is deficient thus leading to accumulation of fructose in blood and its excretion.

Clinical significance

Sorbitol pathway of fructose metabolism

Seminal fluid is rich in fructose and this is the only energy source for the sperms. The metabolic pathways involved are:

1. Reduction of D Glucose to Sorbitol.

2. Oxidation of sorbitol to D fructose.

The formation of sorbitol from glucose proceeds rapidly in the lens of the eye and schwann cells of nervous system.

Sorbitol cannot pass through the cell membrane and in diabetic individuals as the rate of oxidation of sorbitol to fructose decreases sorbitol level in these cells increases.

Elevated sorbitol concentration in these cells causes osmotic pressure which may be responsible for the development of cataracts of lens of the eye and diabetic neuropathies.

Liver cell necrosis

Fructose when used parenterally for nutrition can cause depletion of adenine nucleotides and thus leads to liver cell necrosis.

Inherited disorder

Hereditary fructose intolerance

An inherited disorder manifesting with severe clinical features

Enzyme defect

Aldolase B deficiency

Clinical features

1. Nausea

2. Vomiting

3. Profuse sweating

4. Slight Icterus (medical name for jaundice)

5. Albuminuria

6. Aminoaciduria

7. Hypoglycemia

Diagnosis

1. Phenylhydrazine test

2. Fructose tolerance test

3. Seliwanoff test

Treatment

Fructose and sucrose must be restricted in the diet.

The sources of fructose such as honey must also be restricted.