General Discussion
Fructosuria is a rare but benign inherited metabolic disorder. It is characterized by the
excretion of fruit sugar (fructose) in the urine. Normally, no fructose is excreted in the
urine. This condition is caused by a deficiency of the enzyme fructokinase in the liver.
This enzyme is needed for the synthesis of glycogen (the body's form of stored energy)
from fructose. The presence of fructose in the blood and urine may lead to an incorrect
diagnosis of diabetes mellitus.
General Discussion
Fructosuria is a rare but benign inherited metabolic disorder. It is characterized by the
excretion of fruit sugar (fructose) in the urine. Normally, no fructose is excreted in the
urine. This condition is caused by a deficiency of the enzyme fructokinase in the liver.
This enzyme is needed for the synthesis of glycogen (the body's form of stored energy)
from fructose. The presence of fructose in the blood and urine may lead to an incorrect
diagnosis of diabetes mellitus.
Signs & Symptoms
Fructosuria is characterized by the presence of fructose in the urine. There are no other
symptoms. However, the fructose may be mistaken for glucose (blood sugar) leading to
an incorrect diagnosis of Diabetes Mellitus.
Causes
Fructosuria is a rare hereditary disorder transmitted as an autosomal recessive trait.
The defective gene has been mapped to the Gene Map Locus 2p23.3-p23.2.
Chromosomes, which are present in the nucleus of human cells, carry the genetic
characteristics of each individual. Pairs of human chromosomes are numbered from 1
through 22, with an unequal 23rd pair of X and Y chromosomes for males, and two X
chromosomes for females. Each chromosome has a short arm designated as p and a
long arm identified by the letter q. Chromosomes are further subdivided into many
bands that are numbered. For example, chromosome 2p23.3 refers to band 23 on the
short arm of chromosome 2.
Recessive genetic disorders occur when an individual inherits the same abnormal gene
for the same trait from each parent. If an individual receives one normal gene and one
gene for the disease, the person will be a carrier for the disease, but usually will not
show symptoms. The risk for two carrier parents to both pass the defective gene and,
therefore, have an affected child is 25% with each pregnancy. The risk to have a child
who is a carrier like the parents is 50% with each pregnancy. The chance for a child to
receive normal genes from both parents and be genetically normal for that particular
trait is 25%. The risk is the same for males and females.
All individuals carry 4-5 abnormal genes. Parents who are close relatives
(consanguineous) have a higher chance than unrelated parents to both carry the same
abnormal gene, which increases the risk to have children with a recessive genetic
disorder.
Affected Populations
Fructosuria affects about 1 out of every 130,000 persons in the United States. It affects
males and females in equal numbers.
Related Disorders
Comparison of the following disorder with Fructosuria may be useful for a differential
diagnosis:
Diabetes Mellitus is a common disorder in which the body does not produce enough
insulin and is, therefore, unable to convert nutrients into the energy necessary for daily
activity. The disorder affects females and males approximately equally. Although the
causes of Insulin-Dependent Diabetes are not known, genetic factors seem to play a
role. Symptoms of Diabetes Mellitus can be very debilitating if left untreated, whereas
Fructosuria does not cause excessive thirst, weight loss or fatigue. (For more
information, choose Diabetes as your search term in the Rare Disease Database.)
Standard Therapies
Diagnosis of Fructosuria is made by testing the urine for the presence of fructose.
Fructosuria does not require treatment as the symptoms are harmless.
