There are more than 400 genetically determined variants of glucose-6-phosphate dehydrogenase deficiency described by the end of 1989. 3.Different molecular forms of the enzyme were exhibited, distinguished by their different electrophoretic mobility and kinetic properties. 7.It is now a convention to categorise the variants into five classes according to the residual enzyme activity based on criteria established by the World Health Organisation (WHO). 4. The Mediterranean and the African (A-) variants are by far the most clinically significant. Enzyme activity is scarcely detectable in the Mediterranean type but close to normal in the African variant. Therefore, the latter variant is considered to be the less severe form of glucose-6-phosphate dehydrogenase deficiency. 1. 3.
More recently, the development of new gene cloning techniques and complementary DNA (deoxyribonucleic acid) sequencing techniques have made it possible to identify the precise mutation of even the variants with the lowest residual activity. Many variants previously thought to be unique have proved to be identical. 3.The majority of the variants arose from a single point-mutation resulting in amino acid substitution in the structural gene encoding for glucose-6-phosphate dehydrogenase which is located at the Xq28 region on the tip of the long arm of the X- chromosome. 4. 8.
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Prepared on 01 Jan 2008 by teekoonhien |
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