Favism (from Latin: faba = bean) is an X-linked recessive inherited metabolic disease caused by a glucose-6-phosphate dehydrogenase (G6PD) deficiency. The enzyme glucose-6-phosphate dehydrogenase plays a key role in the pentose phosphate pathway and catalyses the conversion of glucose-6-phosphate to D-glucono-1,5-lactono-6-phosphate. This produces reduction equivalents such as NADPH that protect certain cell structures (e.g., erythrocyte membranes) from oxidative damage. The cell loses this protective mechanism due to the G6PD enzyme deficiency and hemolytic anemia occurs.
Various pathogenic variants in the G6PD gene lead to G6PD deficiency. The residual enzymatic activity and thus the symptom expression varies depending on the variant. G6PD deficiency is divided into different classes according to the enzyme activity measured.
Due to the X-linked chromosomal inheritance, it is mainly men who are affected. Hemizygous men and homozygous or combined heterozygous women with variants on the X chromosome show the fully developed phenotype. Heterozygous female carriers usually show symptoms only if there is a preferential expression of the allele in question, e.g., due to delayed X-inactivation. The prevalence is 0.14-0.37% among the German population, and in some countries of the Mediterranean, Africa and Asia it is 3-35%. In the Western European population, the Mediterranean form caused by variant c.563C>T [p.(Ser188Phe)] is the most common cause of favism and it leads to a severe course of disease (WHO class II). Drugs with an oxidative effect can trigger hemolytic-anemic crises and should therefore only be prescribed after a thorough risk-benefit analysis. Fava bean proteins (aglycones) and its pollen also trigger hemolytic events.
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