Dulcitol
Encyclopedia
Galactitol is a sugar alcohol
, the reduction
product of galactose
. In people with galactokinase deficiency
, a form of galactosemia
, excess dulcitol forms in the lens
of the eye leading to cataract
s.
Galactitol is produced from galactose
in a reaction catalyzed by aldose reductase
. Galactose itself comes from the metabolism of the disaccharide lactose
into glucose
and galactose.
The other common galactose metabolism defect is a defect in galactose-1-phosphate uridylyltransferase
, an autosomal recessive disorder, which also causes a buildup of galactitol as a result of increased concentrations of galactose-1-phosphate and galactose. The toxicity associated with galactose-1-phosphate uridylyltransferase
deficiency is associated with symptoms of hepatosplenomegaly
and mental retardation
in addition to the cataracts caused by galactitol buildup.
Sugar alcohol
A sugar alcohol is a hydrogenated form of carbohydrate, whose carbonyl group has been reduced to a primary or secondary hydroxyl group . Sugar alcohols have the general formula Hn+1H, whereas sugars have HnHCO...
, the reduction
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
product of galactose
Galactose
Galactose , sometimes abbreviated Gal, is a type of sugar that is less sweet than glucose. It is a C-4 epimer of glucose....
. In people with galactokinase deficiency
Galactokinase deficiency
Galactokinase deficiency, also known as Galactosemia type 2 or GALK deficiency, is an autosomal recessive metabolic disorder marked by an accumulation of galactose and galactitol secondary to the decreased conversion of galactose to galactose-1-phosphate by galactokinase...
, a form of galactosemia
Galactosemia
Galactosemia is a rare genetic metabolic disorder that affects an individual's ability to metabolize the sugar galactose properly. Although the sugar lactose can metabolize to galactose, galactosemia is not related to and should not be confused with lactose intolerance...
, excess dulcitol forms in the lens
Lens (anatomy)
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...
of the eye leading to cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
s.
Galactitol is produced from galactose
Galactose
Galactose , sometimes abbreviated Gal, is a type of sugar that is less sweet than glucose. It is a C-4 epimer of glucose....
in a reaction catalyzed by aldose reductase
Aldose reductase
Aldose reductase is an NADPH-dependent oxidoreductase that catalyzes the reduction of a variety of aldehydes and carbonyls, including monosaccharides...
. Galactose itself comes from the metabolism of the disaccharide lactose
Lactose
Lactose is a disaccharide sugar that is found most notably in milk and is formed from galactose and glucose. Lactose makes up around 2~8% of milk , although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from or , the Latin word for milk,...
into glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
and galactose.
The other common galactose metabolism defect is a defect in galactose-1-phosphate uridylyltransferase
Galactose-1-phosphate uridylyltransferase
Galactose-1-phosphate uridylyltransferase is an enzyme responsible for converting ingested galactose to glucose.Galactose-1-phosphate uridylyltransferase catalyzes the second step of the Leloir pathway of galactose metabolism, namely:The expression of GALT is controlled by the actions of the...
, an autosomal recessive disorder, which also causes a buildup of galactitol as a result of increased concentrations of galactose-1-phosphate and galactose. The toxicity associated with galactose-1-phosphate uridylyltransferase
Galactose-1-phosphate uridylyltransferase
Galactose-1-phosphate uridylyltransferase is an enzyme responsible for converting ingested galactose to glucose.Galactose-1-phosphate uridylyltransferase catalyzes the second step of the Leloir pathway of galactose metabolism, namely:The expression of GALT is controlled by the actions of the...
deficiency is associated with symptoms of hepatosplenomegaly
Hepatosplenomegaly
Hepatosplenomegaly is the simultaneous enlargement of both the liver and the spleen . Hepatosplenomegaly can occur as the result of acute viral hepatitis or infectious mononucleosis, or it can be the sign of a serious and life threatening lysosomal storage disease...
and mental retardation
Mental retardation
Mental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...
in addition to the cataracts caused by galactitol buildup.