Enzymopathies = ENZYME DEFECTS G6PD Deficiency (Glucose 6 phosphate dehydrogenase Deficiency)

Objectives To review the role of G6PD enzyme, and the red cell metabolism. To define G6PD deficiency as a hemolytic anemia. List the lab. Findings in G6PD deficiency.

G6PD deficiency is an inherited condition G6PD deficiency is an inherited condition. Which cause a non immune hemolytic anemia. Commonest red cell enzymopathy affecting over 400 million people world wide. The G6PD enzyme catalyzes an oxidation/reduction reaction. G6PD in red cell essential for preventing Oxidative damage to red cells So cell lacking the enzyme are susceptible to oxidant induced hemolysis.

G6PD functions in catalyzing the oxidation of G6P to 6-phosphogluconate, while reducing NADP to NADPH; this is the first step in the pentose phosphate pathway. So G6PD is responsible for maintaining adequate levels of NADPH inside the cell. NADPH is used to keep glutathione, in its reduced form . Reduced glutathione acts as a scavenger كنّاس for dangerous oxidative metabolites in the cell; it converts harmful hydrogen peroxide to water . There are other metabolic pathways that can generate NADPH in all cells, except in red blood cells where other NADPH-producing enzymes are lacking.

G6PD deficiency is also sometimes referred to as favism since some G6PD deficient individuals are also allergic to fava beans. All patients with favism are G6PD deficient, but many G6PD-deficient individuals can regularly eat fava beans

Sex-linked inheritance. Affect males. Females are carriers Sex-linked inheritance. Affect males. Females are carriers.(they have ½ of RBCs with normal enzyme activity). G6PD activity is  mostly in old cells.

CLINICALLY Usually a symptomatic. Acute hemolysis due to oxidant stress. E.g. : Drugs, Infection, fava beans. Hemolysis is Intravascular. (Hemoglobinuria). The anemia may be self-limiting because new red cells (with normal enzyme activity) are produced. Neonatal jaundice.

Lab. Diagnosis Between crisis, blood count is normal. During crisis, features of intravascular hemolysis. Blood film show : contracted & fragmented cells. Bite/Blister cells : loss of cytoplasm with separation of remaining Hb from cell membrane. Subravital stain : Heinz bodies oxidized denatured Hb. Reticulocytosis during hemolysis.

Bite cells/Blister cells Bite عضة أو قضمة cells are formed when Heinz bodies (the product of oxidant stress on the haemoglobin molecule) together with some red cell content, are removed from red cells as they pass through the spleen. When the red cell membrane around the bite repairs, a blister-like structure forms, hence the term blister cell. Blister = بثرة أو قرحة

arrow indicates a “bite” cell, or keratocyte

arrows indicate “blister cells,” and arrowheads irregularly contracted cells

Heinz bodies are red cells’ inclusions composed of oxidized denatured hemoglobin. Heinz bodies appear as small round inclusions within the red cell, though when stained with Romanowsky stains they may appear as projections from the cell. They appear more clearly when supravitally stained

6. Screening Tests for G6PD Deficiency Flurescent Screening test. (G6PD will produce NADPH from NADP+.These NADPHs will fluoresces under UV light. In G6PD deficiency,less fluoresces occur due to less NADPH production) Methaemoglobin Reduction test . During and immediately after a hemolytic episode, tests may yield false-negative results because of destruction of the older, more deficient RBCs and the presence of reticulocytes rich in G6PD.

7. Enzyme assay Spectrophotometric enzyme assays. The activity of the enzyme is assayed by following the rate of production of NADPH, which, unlike NADP, has a peak of UV light absorption at 340 nm.