47
GALE Deficiency Galactosemia
This condition is extremely rare showing the same clinical presentations like that of
GALT deficiency including vomiting, jaundice, and hepatomegaly. GALE deficiency causes the accumulation of galactitol and galactose-1-P [15]. Newborns having a severe deficiency of GALE enzyme must be on diet excluded from lactose but
in most cases do not require a restriction of galactose [13].
Cataracts
A progressive opacity of the lens is termed as cataracts which result from molecular
damage [16]. GALK deficiency is the leading cause of cataracts showing no damage
to the kidney, liver, and brain, though GALK deficiency can lead to pseudo-tumor
cerebri in some cases. Due to this enzyme deficiency, phosphorylation of galactose
into galactose-1-phosphate is inhibited which results in the accumulation of galactose and galactitol, the latter is accumulated in the lens leading to osmotic swelling
of lens fibers and hence protein denaturation [13, 17]. Exclusion of diet containing
lactose is the primary intervention for its treatment [13].
Metabolic Disorders Induced by Impaired Fructose
Metabolism
Fructose is a major sweetening agent in a human diet which may be in free form as
in honey, some fruits, and in many vegetables or maybe a disaccharide as sucrose
which consists of glucose and fructose. Sorbitol is also a source of fructose present
in some fruits and vegetables [18]. Fructose and glucose are being used in many
metabolic pathways including glycolysis, Krebs cycle, glycogenolysis, gluconeogenesis, pentose phosphate shunt, and Cori cycle [19]. Fructose metabolism undergoes in the liver, renal cortex, and mucosa of small intestine catalyzed by
fructokinase, aldolase B, and triose-kinase [18]. By phosphorylation process catalyzed by fructokinase, fructose is converted into fructose-1-phosphate, which is
then split into two compounds dihydroxyacetone phosphate (DAP) and triose glyceraldehyde, the reaction being catalyzed by fructose-1-phosphate aldolase. DAP
then undergoes glycolytic pathway, whereas glyceraldehyde can undergo three
metabolic pathways (a) phosphorylated to glyceraldehyde phosphate by the action
of triose-kinase, (b) oxidized to glycerol by glycerol kinase, and (c) oxidized to
glyceric acid and then phosphoglycerate by the action of glyceric acid kinase [20].
Three inborn disorders have been identified from impaired fructose metabolism
caused by the deficiency of its three enzymes that include essential fructosuria,
hereditary fructose intolerance, and the fructose-1,6-biphosphatase deficiency [18].
2 Impaired Carbohydrate Metabolism in Metabolic Disorders
GALE Deficiency Galactosemia
This condition is extremely rare showing the same clinical presentations like that of
GALT deficiency including vomiting, jaundice, and hepatomegaly. GALE deficiency causes the accumulation of galactitol and galactose-1-P [15]. Newborns having a severe deficiency of GALE enzyme must be on diet excluded from lactose but
in most cases do not require a restriction of galactose [13].
Cataracts
A progressive opacity of the lens is termed as cataracts which result from molecular
damage [16]. GALK deficiency is the leading cause of cataracts showing no damage
to the kidney, liver, and brain, though GALK deficiency can lead to pseudo-tumor
cerebri in some cases. Due to this enzyme deficiency, phosphorylation of galactose
into galactose-1-phosphate is inhibited which results in the accumulation of galactose and galactitol, the latter is accumulated in the lens leading to osmotic swelling
of lens fibers and hence protein denaturation [13, 17]. Exclusion of diet containing
lactose is the primary intervention for its treatment [13].
Metabolic Disorders Induced by Impaired Fructose
Metabolism
Fructose is a major sweetening agent in a human diet which may be in free form as
in honey, some fruits, and in many vegetables or maybe a disaccharide as sucrose
which consists of glucose and fructose. Sorbitol is also a source of fructose present
in some fruits and vegetables [18]. Fructose and glucose are being used in many
metabolic pathways including glycolysis, Krebs cycle, glycogenolysis, gluconeogenesis, pentose phosphate shunt, and Cori cycle [19]. Fructose metabolism undergoes in the liver, renal cortex, and mucosa of small intestine catalyzed by
fructokinase, aldolase B, and triose-kinase [18]. By phosphorylation process catalyzed by fructokinase, fructose is converted into fructose-1-phosphate, which is
then split into two compounds dihydroxyacetone phosphate (DAP) and triose glyceraldehyde, the reaction being catalyzed by fructose-1-phosphate aldolase. DAP
then undergoes glycolytic pathway, whereas glyceraldehyde can undergo three
metabolic pathways (a) phosphorylated to glyceraldehyde phosphate by the action
of triose-kinase, (b) oxidized to glycerol by glycerol kinase, and (c) oxidized to
glyceric acid and then phosphoglycerate by the action of glyceric acid kinase [20].
Three inborn disorders have been identified from impaired fructose metabolism
caused by the deficiency of its three enzymes that include essential fructosuria,
hereditary fructose intolerance, and the fructose-1,6-biphosphatase deficiency [18].
2 Impaired Carbohydrate Metabolism in Metabolic Disorders