G6PD Deficiency is a hereditary abnormality in the activity of an erythrocyte (red blood cell) enzyme. This enzyme, glucose-6-phosphate dehydrogenase (G-6-PD), is essential for assuring a normal life span for red blood cells, and for oxidizing processes. This enzyme deficiency may provoke the sudden destruction of red blood cells and lead to hemolytic anemia with jaundice following the intake of fava beans, certain legumes and various drugs (see a complete list of drugs and foodstuffs to avoid).
The defect is sex-linked, transmitted from mother (usually a healthy carrier) to son (or daughter, who would be a healthy carrier too; see a diagram of inheritance probabilities). This is due to the fact that the structure of G-6-PD is carried on the X chromosome: As stated by Ernest Beutler, M.D., "in females, only one of the two X chromosomes in each cell is active; consequently, female heterozygotes for G-6-PD deficiency have two populations of red cells; deficient cells and normal cells."
The deficit is most prevalent in Africa (affecting up to 20% of the population), but is common also around the Mediterranean (4% - 30%) and southeast Asia. Please note that there are more than 400 genetic variants of the deficiency. You can determine whether you are G-6-PD deficient by a simple blood test. To determine your variant, you must test yourself at specialized genetic labs.