6-phosphogluconate dehydrogenase deficiency | |
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Crystallographic structure of sheep 6-phosphogluconate dehydrogenase complexed with adenosine 2'-monophosphate [1] |
6-phosphogluconate dehydrogenase | |||||||||
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Identifiers | |||||||||
Symbol | 6PGD | ||||||||
Pfam | PF00393 | ||||||||
Pfam clan | CL0106 | ||||||||
InterPro | IPR006114 | ||||||||
PROSITE | PDOC00390 | ||||||||
SCOP2 | 2pgd / SCOPe / SUPFAM | ||||||||
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6-Phosphogluconate dehydrogenase deficiency (6PGD deficiency), or partial deficiency, is an autosomal hereditary disease characterized by abnormally low levels of 6-phosphogluconate dehydrogenase (6PGD), a metabolic enzyme involved in the Pentose phosphate pathway. It is very important in the metabolism of red blood cells (erythrocytes). 6PDG deficiency affects less than 1% of the population, and studies suggest that there may be race variant involved in many of the reported cases. Although it is similar, 6PDG deficiency is not linked to glucose-6-phosphate dehydrogenase (G6PD) deficiency, as they are located on different chromosomes. However, a few people have had both of these metabolic diseases.
Many patients with 6-phosphogluconate dehydrogenase deficiency are carriers and have no symptoms. It has been discovered that symptoms manifest more frequently in female carriers. Depending on how severe the deficiency is, it has been demonstrated that enzyme activity is reduced by 35–65%.
Abnormal red blood cell breakdown (hemolysis) in 6PGD deficiency can be symptomatic in a number of ways, including the following:
6PGD deficiency is a recessive hereditary disorder located on the P arm of chromosome 1. It is an autosomal disease, not associated with the sex chromosomes and can affect both sexes. The lack of synthesis of a specific protein on chromosome 1 has reduced a subject suffering from 6PGD deficiency from producing adequate amounts of the 6-phosphogluconate dehydrogenase enzyme. Transfer of the disease can be passed from a parent, even when the parent is asymptomatic.
6-Phosphogluconate dehydrogenase (6PGD) is an enzyme in the pentose phosphate pathway (see image). 6PGD catalyzes the reaction of 6-phosphogluconate to an unstable form of 3-keto-6-phosphogluconate, and yields a co-enzyme nicotinamide adenine dinucleotide phosphate (NADPH) as a byproduct. NADPH supplies reducing power to cells. The reaction is the second NADPH releasing reaction in the pentose phosphate pathway, the first being catalyzed by glucose-6-phosphate dehydrogenase. 3-keto-6-phosphogluconate then rapidly (in an irreversible reaction) decarboxylates to CO2 and ribulose-5-phosphate, which is the precursor to many vital metabolic processes.
The NADPH pathway (both 6PGD and G6PD reactions) is the only source of reductant to reduce glutathione in red blood cells. The role of erythrocytes as oxygen carriers puts them at risk of being damaged by oxidizing free radicals. The reduction of glutathione acts as an antioxidant and prevents damage from reactive oxygen species.
People suffering from 6PGD or G6PD deficiency (or both) are at risk of hemolytic anemia in states of oxidative stress. Oxidative stress can result from infection and from chemical exposure to medication and certain foods. Broad beans, e.g., fava beans, contain high levels of vicine, divicine, convicine and isouramil, all of which are oxidants.
When all remaining reduced glutathione is consumed, enzymes and other proteins, such as hemoglobin are subsequently damaged by the free radicals, leading to electrolyte imbalance, cross-bonding and protein deposition in the red cell membranes. Damaged red cells are phagocytosed and sequestered (taken out of circulation) in the spleen. The hemoglobin is metabolized to bilirubin (causing jaundice). The red blood cells rarely disintegrate in the circulation, so hemoglobin is rarely excreted directly by the kidney, but this can occur in severe cases, causing acute kidney injury.
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The most important measure taken for treatment of 6-phosphoglucanate dehydrogenase is prevention. Avoidance of chemical exposures to drugs and foods that have the potential to cause hemolysis. Although some foods and supplements have antioxidant properties, their use does not decrease the severity of G6PD deficiency.
Diagnosis is difficult during haemolytic episodes since reticulocytes have increased levels of enzymes and may produce erroneously normal results. Testing can be useful after a steady state is reached (about six weeks after the most recent episode of haemolysis), including a G6PD assay to confirm a diagnosis and G6PD spectrophotometry to detect the level of activity.
Vaccinations against some common pathogens (e.g. hepatitis A and hepatitis B) may prevent infection-induced attacks. [2]
In the acute phase of hemolysis, blood transfusions might be necessary, or even dialysis in acute kidney injury. Blood transfusion is an important symptomatic measure, as the transfused red cells are generally not 6PGD deficient and will live a normal lifespan in the recipient's circulation.
Hemolysis or haemolysis, also known by several other names, is the rupturing (lysis) of red blood cells (erythrocytes) and the release of their contents (cytoplasm) into surrounding fluid. Hemolysis may occur in vivo or in vitro.
Glucose-6-phosphate dehydrogenase deficiency (G6PDD), which is the most common enzyme deficiency worldwide, is an inborn error of metabolism that predisposes to red blood cell breakdown. Most of the time, those who are affected have no symptoms. Following a specific trigger, symptoms such as yellowish skin, dark urine, shortness of breath, and feeling tired may develop. Complications can include anemia and newborn jaundice. Some people never have symptoms.
Glucose 6-phosphate is a glucose sugar phosphorylated at the hydroxy group on carbon 6. This dianion is very common in cells as the majority of glucose entering a cell will become phosphorylated in this way.
Hemolytic anemia or haemolytic anaemia is a form of anemia due to hemolysis, the abnormal breakdown of red blood cells (RBCs), either in the blood vessels or elsewhere in the human body (extravascular). This most commonly occurs within the spleen, but also can occur in the reticuloendothelial system or mechanically. Hemolytic anemia accounts for 5% of all existing anemias. It has numerous possible consequences, ranging from general symptoms to life-threatening systemic effects. The general classification of hemolytic anemia is either intrinsic or extrinsic. Treatment depends on the type and cause of the hemolytic anemia.
Hemoglobinuria is a condition in which the oxygen transport protein hemoglobin is found in abnormally high concentrations in the urine. The condition is caused by excessive intravascular hemolysis, in which large numbers of red blood cells (RBCs) are destroyed, thereby releasing free hemoglobin into the plasma. Excess hemoglobin is filtered by the kidneys, which excrete it into the urine, giving urine a purple color. Hemoglobinuria can lead to acute tubular necrosis which is an uncommon cause of a death of uni-traumatic patients recovering in the ICU.
Nicotinamide adenine dinucleotide phosphate, abbreviated NADP+ or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NADPH as a reducing agent ('hydrogen source'). It is used by all forms of cellular life.
The pentose phosphate pathway is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses as well as ribose 5-phosphate, a precursor for the synthesis of nucleotides. While the pentose phosphate pathway does involve oxidation of glucose, its primary role is anabolic rather than catabolic. The pathway is especially important in red blood cells (erythrocytes).
Glucose-6-phosphate dehydrogenase (G6PD or G6PDH) (EC 1.1.1.49) is a cytosolic enzyme that catalyzes the chemical reaction
Glutathione reductase (GR) also known as glutathione-disulfide reductase (GSR) is an enzyme that in humans is encoded by the GSR gene. Glutathione reductase catalyzes the reduction of glutathione disulfide (GSSG) to the sulfhydryl form glutathione (GSH), which is a critical molecule in resisting oxidative stress and maintaining the reducing environment of the cell. Glutathione reductase functions as dimeric disulfide oxidoreductase and utilizes an FAD prosthetic group and NADPH to reduce one molar equivalent of GSSG to two molar equivalents of GSH:
Heinz bodies are inclusions within red blood cells composed of denatured hemoglobin. They are not visible with routine blood staining techniques, but can be seen with supravital staining. The presence of Heinz bodies represents damage to hemoglobin and is classically observed in G6PD deficiency, a genetic disorder that causes hemolytic anemia. In veterinary medicine, Heinz bodies may be seen following the consumption of foods containing thiosulfate and propylene glycol compounds by cats, dogs and certain primates.
The polyol pathway is a two-step process that converts glucose to fructose. In this pathway glucose is reduced to sorbitol, which is subsequently oxidized to fructose. It is also called the sorbitol-aldose reductase pathway.
Aldolase A deficiency is an autosomal recessive metabolic disorder resulting in a deficiency of the enzyme aldolase A; the enzyme is found predominantly in red blood cells and muscle tissue. The deficiency may lead to hemolytic anaemia as well as myopathy associated with exercise intolerance and rhabdomyolysis in some cases.
6-Phosphogluconate dehydrogenase (6PGD) is an enzyme in the pentose phosphate pathway. It forms ribulose 5-phosphate from 6-phosphogluconate:
In enzymology, a phosphogluconate dehydrogenase (decarboxylating) (EC 1.1.1.44) is an enzyme that catalyzes the chemical reaction
Ribose-5-phosphate isomerase (Rpi) encoded by the RPIA gene is an enzyme that catalyzes the conversion between ribose-5-phosphate (R5P) and ribulose-5-phosphate (Ru5P). It is a member of a larger class of isomerases which catalyze the interconversion of chemical isomers. It plays a vital role in biochemical metabolism in both the pentose phosphate pathway and the Calvin cycle. The systematic name of this enzyme class is D-ribose-5-phosphate aldose-ketose-isomerase.
Inborn errors of carbohydrate metabolism are inborn error of metabolism that affect the catabolism and anabolism of carbohydrates.
Transaldolase deficiency is a disease characterised by abnormally low levels of the transaldolase enzyme. It is a metabolic enzyme involved in the pentose phosphate pathway. It is caused by mutation in the transaldolase gene (TALDO1). It was first described by Verhoeven et al. in 2001.
Drug-induced nonautoimmune hemolytic anemia is a form of hemolytic anemia.
A degmacyte or bite cell is an abnormally shaped mature red blood cell with one or more semicircular portions removed from the cell margin, known as "bites". These "bites" result from the mechanical removal of denatured hemoglobin during splenic filtration as red cells attempt to migrate through endothelial slits from splenic cords into the splenic sinuses. Bite cells are known to be a result from processes of oxidative hemolysis, such as Glucose-6-phosphate dehydrogenase deficiency, in which uncontrolled oxidative stress causes hemoglobin to denature and form Heinz bodies. Bite cells can contain more than one "bite." The "bites" in degmacytes are smaller than the missing red blood cell fragments seen in schistocytes.
Divicine (2,6-diamino-4,5-dihydroxypyrimidine) is an oxidant and a base with alkaloidal properties found in fava beans and Lathyrus sativus. It is an aglycone of vicine. A common derivative is the diacetate form (2,6-diamino-1,6-dihydro-4,5-pyrimidinedione).