Gloucose-6-Phosphate Dehyadrogenase Deficiency

Gulcose-6-phosphate dehydrogenase (G6PD) is the first enzyme in the hexose monophosphate shunt of the Embden-Meyerhof glycolytic pathway from which red cells derive most of their metabolic energy. The function of this shunt is to service the enzymes glutathione reeducates and glutathione eroxidase, which protect the red cells against damage due to oxidation. This protective mechanism is crippled in the absence of G6PD and certain drugs in sufficient concentration can seriously injure the erythrocyte.

The deficiency is inherited as an X-linked disorder with a high frequency among Black Africans who possess an electrophoresis enzyme is a type (A-) in deficient Black Africans. In Caucasians only the normal B type enzyme is found and the deficient type is also B (B-). In West and East Africa about 20% of males (hemi zygotes) and about 4% of females (homozygous for the abnormal gene) are affected and the enzyme activity is about 15%of normal. Heterozygous females have two populations of red cells, one deficient and the other normal. A total of 100 million persons are affected by this disorder worldwide. The deficiency in Caucasian and Oriental populations is more severe, enzyme activity being less than 1% of normal. Fauvism (haemolytic anemia from the ingestion of the broad bean, Vicia faba )is due to deficiency of G6PD of the severe variety(B-). Some cases of haemolytic disease of the newborn are caused by this deficiency. Other rare types of G6PD, biochemically different from the above, may be associated with congenital non-spherocytic haemolytic disease and occur sporadically in all races.

Many drugs in common clinical use-for example, some antimalarials (dapsone) and sulphonamides-are capable of precipitating haemolysis in individuals with G6PD deficiency. Infections may also potentate the haemolytic action of drugs such as aspirin, chloramphenicol and chloroquine. 

Investigations

The diagnosis can be confirmed by estimating the G6Pd activity of the red cell but this may not be entirely accurate if there is considerable reticulocytosis. A number of screening rests are usually present: haemoglobinaemia, methaemalbuminaemia, baemoglobinuria, ahaptoglobinaemia and later haemosiderinuria.

Mangement

This is by removal of the toxic agent. Recovery is usually rapid but if the anemia is severe, transfusion of red cells with a normal enzyme complement may be required. Thereafter, the patient should be advised to avoid drugs, which may precipitate the disorder. Splenectomy is without value.

BACK

NEXT