Glucose-6-phosphate dehydrogenase deficiency is essentially a genetically heterogeneous condition. 4.This explains why glucose-6-phosphate dehydrogenase deficiency is predominantly a male syndrome. Since males possess only one copy of the gene encoding for glucose-6-phosphate dehydrogenase, they are either normal or glucose-6-phosphate dehydrogenase deficient. The females on the other hand can be either normal, heterozygous or homozygous (where no normal glucose-6-phosphate dehydrogenase is made). 1.However, it is often quite difficult to differentiate between them based on the phenotypic expression alone. 7.
Heterozygous females with glucose-6-phosphate dehydrogenase deficiency were shown to have two red blood cells populations, one that was normal and one that was enzyme deficient. 3.This is because one copy of the gene governs the synthesis of the normal glucose-6-phosphate dehydrogenase and the other makes the variant. In the early embryonic stage of life one of the two X-chromosomes is inactivated, hence each cell afterwards synthesise only either the normal or the deficient enzyme. 1.This phenomenon offers an insight into why female heterozygotes appear to have a greater resistance against P. falciparum malaria than do deficient male hemizygotes. 3. 4.
The growth of malarial parasites is naturally impaired upon first passage from normal to glucose-6-phosphate dehydrogenase deficient red blood cells. Through subsequent passages, they could adapt and grow normally though by inducing their own production of glucose-6-phosphate dehydrogenase to protect it against oxidative damage. In heterozygous glucose-6-phosphate dehydrogenase deficient females however, such adaptation is not possible due to the presence of a mosaic of deficient and normal red blood cells, hence the protection against malaria. 4.
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Prepared on 01 Jan 2008 by teekoonhien |
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