Red Cell Enzyme Deficiency(G6PD)
Red cell utilises glucose which is main metabolic substrate. Deficiency of enzymes lead to development of haemolytic anaemia. Presentaion of these cases may asymptomatic or severe haemolytic anaemia or jaundice due to increased un conjugated bilirubin.
Common enzyme deficiencies are Glucose 6-phosphate dehydrogenase(G6PD) deficiency, path way of enzyme. Pyruvate kinase(PK) deficiency of glycolytic path way of red cell metabolism.
G6PD deficiency is the most common red cell enzymopathy. More than 7% of world population having defective gene. Thegene is located on X chromosome(Xq28).
Main Variants of G6PD deficiency are G6PD B(normal or wild type) found mostly in Asians. It is nor associated with haemolysis.
G6PD A+ mostly found in African black population. It is not associated with haemolysis.
G6PDA-. It is associated with mild to moderate haemolysisand is mostly found in African Americans.
G6PD Mediterranean is most common variant found in middle east and India. The red cells of all ages are affected. It’s associated with severe haemolysis.
G6PD deficiency is also increased were in the epidemic region of Falciparum Malaria. It is due to oxidative stress that causes deficiency of GSH destroy the host red cells and also kills the parasite.
According to WHO G6PD variants have been grouped in 5 variants depending upon the enzyme activity and the severity of haemolysis.
Red cells contain high concentration of reduced glutathione(GSH). It is essential to protecting protein and haemoglobin from oxidate radicals is not converting in to water with the help of glutathione peroxide enzyme.
In deficiency of G6PD, enogh GSH is not available so that H2O2 is not detoxified and accumulate in the cell which causes of oxidation of haemoglobin.
G6PD deficient person when exposed to oxidant may suffer from attack of haemolysis and shows the following symptoms like jaundice, Dark coloured urine indicate haemoglobinuria and anaemia.
Laboratory Findings: Complete blood count haemoglobinreduced.
Peripheral smear examination shows presence of spherocytes, bite cell, polychromatophills and Heinz bodies.
Indirect bilirubin and LDH raised.
Haemoglobinuria.
For specific diagnosis:
- Methaemoglobin reduction test
- Fluorescent spot test
- Ascorbate cyanide test.
Methaemoglobin reduction test (MRT): EDTA blood sample is treated with sodium nitrate to convert oxyhaemoglobin into methaemoglobin. It is then furtherincubated with methylene blue, the pentose phosphate pathway is stimulated in the subject with normal G6PD activity is reduced.
If there is deficiency of G6PD activity methaemoglobin is not reduced to HbO2 and thus remain in the solution shows brown colour.
In persons with normal G6PD activity it is reduced to HbO2, thus shows red colour.
Fluorescent Spot Test: The principle of the test is that the presence of G6PD in the blood sample, NADP is converted to NADPH which can be detected by the property of impartingfluorescence in ultraviolet light, where as NADP does not impart fluorescence.
