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Glucose-6-phosphate dehydrogenase deficiency is an X-linked recessive hereditary disease characterised by abnormally low levels of glucose-6-phosphate dehydrogenase (abbreviated G6PD or G6PDH), a metabolic enzyme involved in the pentose phosphate pathway, especially important in red blood cell metabolism. Individuals with the disease may exhibit nonimmune hemolytic anemia in response to a number of causes, most commonly infection or exposure to certain medications or chemicals. G6PD deficiency is closely linked to favism, a disorder characterized by a hemolytic reaction to consumption of broad beans, with a name derived from the Italian name of the broad bean (fava). The name favism is sometimes used to refer to the enzyme deficiency as a whole, although this is misleading as not all people with G6PD deficiency will react to consumption of broad beans.
G6PD deficiency is the most common human enzyme defect.[1]
Most individuals with G6PD deficiency are asymptomatic.
Symptomatic patients are almost exclusively male, due to the X-linked pattern of inheritance, but female carriers can be clinically affected due to lyonization, where random inactivation of an X-chromosome in certain cells creates a population of G6PD-deficient red blood cells coexisting with normal red cells. Abnormal red blood cell breakdown (hemolysis) in G6PD deficiency can manifest in a number of ways:
Favism may be formally defined as a haemolytic response to the consumption of broad beans. All individuals with favism show G6PD deficiency. However, not all individuals with G6PD deficiency show favism. For example, in a small study of 757 Saudi men, more than 42% showed G6PD deficiency, but none reported symptoms of favism, despite fava in the diet.[2] Favism is known to be more prevalent in infants and children, and G6PD genetic variant can influence chemical sensitivity. Other than this, the specifics of the chemical relationship between favism and G6PD are not well understood.
Many substances are potentially harmful to people with G6PD deficiency, although many will not produce symptoms unless taken in high doses. Antimalarial drugs that can cause acute haemolysis in people with G6PD deficiency include primaquine, pamaquine and chloroquine. There is evidence that other antimalarials may also exacerbate G6PD deficiency, but only at higher doses. Sulfonamides (such as sulfanilamide, sulfamethoxazole and mafenide), thiazolesulfone, methylene blue and naphthalene should also be avoided by people with G6PD deficiency, as should certain analgesics (such as aspirin, phenazopyridine and acetanilide) and a few non-sulfa antibiotics (nalidixic acid, nitrofurantoin, and furazolidone).[3][1][4] Henna has been known to cause haemolytic crisis in G6PD-deficient infants.[5]
Aspirin is now considered safe in therapeutic doses.[citation needed]
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