Blood sugar or "glucose" is made when carbohydrates are broken down. Glucose-6-phosphate dehydrogenase is one enzyme involved in the pentose phosphate pathway, a pathway which processes glucose. The main reasons for this pathway is actually not to metabolize dietary sugars but to make ribose-5-phosphate which is important for making DNA and RNA, and to make NADPH which is important for protecting cells from potentially harmful molecules called reactive oxygen species. There are other enzymatic pathways in the body that exist to metabolize dietary sugars, for example the Krebb cycle, so when there is a deficiency of glucose-6-phosphate dehydrogenase the primary concern is for the impact the defeciency may have on the body as a result of a lack of ribose-5-phosphate and NADPH, and not necessarily its affect on blood sugar.
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