Introduction

Carbohydrates are body-building foods with a general structure of CH2O. Carbohydrates may be classified as monosaccharides, disaccharides,  oligosaccharides and polysaccharides. The diet’s most common carbohydrate is starch, which is broken down into simpler sugars during digestion. Carbohydrate metabolism includes processes such as glycolysis, tricarboxylic acid cycle, glucuronic acid cycle, and pentose phosphate pathways. Some errors may arise in carbohydrate metabolism, mostly due to congenital deficiency or the absence of a particular enzyme.

BIOCHEMICAL CAUSE, CLINICAL PRESENTATION AND MANAGEMENT OF THE FOLLOWING CARBOHYDRATE DISORDERS.

These are outlined below.

1. GLYCOGEN STORAGE DISORDERS

These biochemical disorders result from a deficiency or complete absence of one or more of the enzymes required to form and break down glycogen. These disorders include;

• Von Gierke disease: This is also referred to as type I and is due to a deficiency of glucose 6 phosphatase. This enzyme is important for the enzymatic breakdown of glucose 6 phosphates to glucose; therefore, when it is deficient, it accumulates glycogen and partially broken down products. The affected organ is the kidney or liver. The signs of this disease include hypoglycemia, enlarged liver or kidney, ketosis, and impaired growth, among others.
• Pompe’s disease: This is also referred to as type II and is due to a deficiency of acid maltase (lysosomal alpha 1 4 glucosidase. This enzyme catalyzes the breakdown of glycogen into glucose in the lysosomes. Deficiency of this enzyme leads to glycogen accumulation in all organs with lysosomes. Manifestations of this disease include cardiac failure, glycogen accumulation in lysosomes, and early death, among others.
• Cori’s disease>This is also called limit dextrinosis and is due to a congenital lack or deficiency of the debranching enzyme. This enzyme catalyses the breakdown of glycogen branching chains, and therefore its absence results in the accumulation of abnormal glycogen having short outer chains. As a result, patients are usually hypoglycemic.
• Anderson’s disease: This disease is due to the absence of branching enzymes in the liver. The branching enzyme catalyzes the formation of side chains during glycogen formation. This enzyme’s absence or deficiency leads to the accumulation of abnormal glycogen having few branches. These patients usually die early due to cardiac or liver failure.
• Mc Ardles’s disease: This disease is due to the absence of muscle glycogen phosphorylase. This enzyme catalyzes the breakdown of glycogen in the muscle. The effects include exercise-induced muscular pain, and muscle cramps, among others.
• Hers’ disease: This disease is due to a liver glycogen phosphorylase deficiency, which catalyses liver glycogen breakdown. This leads to a high liver glycogen content, mild hypoglycemia and ketosis.
• Tarui’s disease: Tarui’s disease results from a phosphofructokinase deficiency in muscle and erythrocytes. This enzyme catalyzes the conversion of fructose 1 phosphate to fructose 1-6 bis-phosphate in the process of glycolysis. Consequently, deficiency of this enzyme leads to muscle cramps and hemolysis of red blood cells.                                                                                                                                                                                                                                                                                                                                                                                         2. HEREDITARY FRUCTOSE INTOLERANCE

This is due to the enzyme aldolase B deficiency, which catalyses the conversion of fructose 1 phosphate to dihydroxyacetone phosphate and glyceride 3 phosphate. This enzyme’s deficiency leads to the accumulation of fructose 1 phosphate in the liver, consequently inhibiting fructokinase and impairing clearance of fructose from blood. This disease manifests through the following signs, hypoglycemia, fructose 1 phosphate accumulation, and liver and kidney damage.

       3. GLUCOSE 6 PHOSPHATE DEHYDROGENASE DEFICIENCY

This is an X-linked inherited disorder that is due to a deficiency in glucose 6 phosphate dehydrogenase deficiency. This enzyme catalyzes the formation of 6-phosphogluconolactone from glucose 6 phosphate and the formation of NADPH in the pentose phosphate pathway. Deficiency of this enzyme leads to insufficient amounts of NADPH to maintain the levels of reduced glutathione and to detoxify hydrogen peroxide in red blood cells, consequently leading to hemolysis.

         4. GALACTOSEMIA

Galactosemia is an inborn galactose metabolism error due to a deficiency of galactose 1 phosphate uridyl transferase. This enzyme catalyzes the reaction of galactose 1 phosphate and UDP glucose to form UDP galactose and glucose 1 phosphate. The deficiency of this enzyme leads to the accumulation of galactose and galactose 1 phosphate.

         5. ESSENTIAL PENTOSURIA

This is an inborn error of metabolism in the glucuronic acid pathway due to a deficiency of the enzyme L-xylulose dehydrogenase, which catalyzes the conversion of xylulose to xylitol. This defect has no major clinical manifestation.

Conclusion

It is important that the deficiencies in the different enzymes are diagnosed early in life so that a management plan is developed, for example, diet modifications or treatment if possible. Some metabolic disorders, for example, glucose 6 phosphate dehydrogenase(G6PD) deficiency, could result in hemolysis. The hemolysis could lead to anemia in some patients, especially children, which needs to be properly managed. Since G6PD deficiency is genetically acquired, there is no treatment; patients should be taught what foods and drugs to avoid to manage the symptoms.